WoodWorks Shearwalls USA – Change History
This document provides descriptions of all new features, bug fixes, and other changes made to the USA version of the WoodWorks Shearwalls program since Shearwalls 2000.
This file last updated with changes May 25, 2020.
Click on the links below to go to the changes for the corresponding release.
1. Vertical Distribution of Rigid Diaphragm Forces
a) Compounding of Accidental Eccentricity (Bug 2733)
Starting with version 12, the vertical distribution of rigid-diaphragm shear force amplified the torsional effect of accidental eccentricities on lower levels, such that as you moved down the structure, the sum of the shear line forces on a level was increasingly larger than the total of the shear loads from that level and those above. These quantities should be equal apart from the effect of taking the worst-case of positive and negative accidental eccentricities on each level. This effect is usually small, creating shearline forces typically 10% greater than the applied shear force, but the compounding of eccentricities created shear forces much larger than applied loads, and an overly conservative design.
This compounding occurred because the shearline forces created using the effect of accidental eccentricity were applied to the level below and used to determine torsions on that level, so that effectively the center of mass from the upper level was shifted by the accidental eccentricity n-1 times at the base of an n-level structure, when it should only be shifted once.
This has been corrected.
b) Vertical Transfer of Rigid Diaphragm Forces for Cantilevered Diaphragms (Bug 3526)
For all wind and seismic design cases except Directional Method Case 2 wind loads, the program applied the shear line forces from flexible diaphragm analysis on the level above to rigid diaphragm torsional analysis on the level below. This was intended as a convenient way to apply the total loading on the level above at its center of loading to the level below, but can be inaccurate in the case of cantilevered diaphragms such as occur at roof overhangs and where perimeter walls are non-shear walls.
The program now directly applies the total vertically accumulated load from the levels above at the centroid of these loads to the level below, for all design cases. Refer to the on-line Help for a derivation of this methodology.
Note that SDPWS 220.127.116.11 requires diaphragms to be modelled as rigid or semi-rigid for open-front structures, i.e. those with significantly cantilevered diaphragms, and the improvement will affect these buildings.
c) Transfer of Torsional Moment Due to Variable Accidental Eccentricity (Bug 3543)
The method that was used to transfer the torsional moment for rigid diaphragm analysis downwards between levels by applying the upper level force at the center of mass of that force to the level below, assumes that the accidental eccentricities (ae) are the same on each level, however ae's can be different due to a different building width on adjacent levels, or for seismic design, due to different torsional amplification factors Ax from ASCE 7 18.104.22.168. This could lead to an inaccuracy in the torsional analysis used to distribute the seismic forces to shear lines on the lower level.
This has been corrected by applying an effective accidental eccentricity on the level below equal to (aeu*Fu + ael*Fl) / (Fu + Fl), where aeu and ael are the design code mandated ae's on the upper and lower level, and Fu and Fl are the total forces from loads applied on each level. Refer to the Online Help topics on the vertical distribution of rigid diaphragm shear force for a derivation of this adjustment.
In the Torsional Analysis Details output, when this occurs, a line is added to give the effective accidental eccentricity and the adjustment equation. The line showing the total force F used for torsional analysis on the level now shows the value of Fl, the force from loads only on that level. This appears regardless of whether differing ae's exist, as it is useful information at any time.
This issue affects seismic analysis and all-heights wind analysis, as these are the design cases with accidental eccentricities.
To gauge the impact of the change:
For the case of variable ae due to building width D:
Case 1 - A penthouse on the upper level, assuming that the mass per unit foot is the same as on the lower level. The maximum difference occurs when the penthouse is 41% of the lower level width, where the effective ae is 60% of the regular ae.
Case 2 - A 6-story tower where five upper stories are narrow, supported by a podium base that is 3 times the width of the tower. The effective ae is roughly half the regular ae.
Case 3- A building shaped like an inverted pyramid. Such a building would be very non-conservative in that the additional width in two dimensions would not be accounted for on the level below. Such buildings are rare but exist.
For the case of variable ae due to differing Ax:
Case 4 - Adjacent levels, one with Ax at maximum = 3, the other with no Ax = 1, otherwise identical. The effective ae on the lower level is twice the ordinary ae. Although not realistic, this serves as a limit to the effect for a 2-storey structure.
Case 5 - Adjacent levels, one with Ax that defines the extreme torsional irregularity 1b = 1.36, the other Ax = 1. The effective ae is 18% larger than the regular ae.
Case 6 - 5 irregular stories on top of a regular base, which could easily happen if the upper levels have openings on one side. If the Ax on the upper levels is 1.3, the effective ae on the base is 1.25 times the regular ae.
2. Torsional Amplification Factor Ax and Torsional Irregularities
The below changes pertain to the torsional amplification factor Ax from ASCE 22.214.171.124 that is applied to accidental eccentricity for torsional analysis and to the determination of Torsional Irregularity from Table 12.3-1.
a) Torsional Irregularity Exemption to Accidental Eccentricity by Structure vs. Level (Bug 3546)
The program was applying the stipulation introduced in ASCE 7-16 126.96.36.199 that accidental eccentricities be applied only in the presence of torsional irregularities on a level-by-level basis, so that some levels could include the 5% extra eccentricity and some not. However, accidental eccentricity is now applied on each level if a torsional irregularity exists anywhere on the structure, because
- 188.8.131.52 says that “Structures … where a torsional irregularity exists … by multiplying Mta [the accidental torsional moment] at each level….[by Ax, the torsional sensitivity factor]. Mta would have to exist on each level for it to be multiplied on each level.
- Commentary 184.108.40.206 says that the amplification of accidental eccentricity is a “system level phenomenon … not explicitly related to an individual story”
- The Commentary to 220.127.116.11 regarding accidental torsion refers to “Irregular structures” in several places, not irregular levels.
This was a non-conservative error where it occurred. It could be particularly large for a base level of a structure with a small difference in displacements, with torsionally sensitive levels above, due for example to openings on one side of the upper levels.
b) Displacement used for Ax Factor (Bug 3521)
When calculating Ax the program was using shear wall defections on the level x only, but according to Commentary C18.104.22.168, introduced ASCE 7-16, they should be the cumulative lateral displacements from the base of the structure up to and including level x. Shearwalls now uses these deflections.
The factor Ax is calculated using displacements δ on extreme perimeter shear walls on each level of the structure, where Ax = (δmax / 1.2 δavg)2. It applies only to Seismic Design Categories C-F. 22.214.171.124 also says that Ax is a “system level phenomenon … not explicitly related to an individual story”
Note that when determining torsional irregularities from Table 11.3-1 via a similar procedure, the per-story deflections are used, also according to C126.96.36.199.
The use of story displacements was conservative for levels with large differences in displacements that have levels with less of a disparity below, or levels below whose torsional characteristics are reversed. It will be non-conservative for levels that have levels below that are more have a greater difference in deflections.
Note that the probability of a large error is made smaller by the fact that the shearline forces responsible for the deflections are transferred from the upper levels to the lower and contribute to the calculation of Ax on the lower level,.
c) Hold-down Forces Used to Determine Displacements for Ax and Torsional Irregularities (Bug 3351)
In detecting Torsional Irregularities or calculating Ax, the program was using hold-down forces derived from the worst case of positive or negative accidental eccentricities to calculate the displacements used for both the positive and negative eccentricities. The effect of this was to increase the lesser of the deflections and reduce the difference in displacements that creates torsional irregularity or a larger Ax.
This has been corrected, and hold, down forces are calculated for the positive and negative eccentricities independently for the purpose of calculating Ax and irregularity.
d) Ax Factor and Torsional Irregularity Determination in Design Iterations (Bug 3547)
The following changes have been made to the implementation of the of the torsional amplification factor Ax from ASCE 188.8.131.52 .and the determination of Torsional Irregularity from Table 12.3-1 in the iterations used in the shear wall design process. These iterations also involve the redundancy factor ρ. (Refer to the Shearwalls Online Help topic about Design iterations for more information on these iterations).
i. Iteration for Accidental Eccentricity Based on Torsional Irregularity
The program would perform a second iteration setting Ax to a value greater than one in the determination of accidental eccentricity only if the initial iteration determined that there was a torsional irregularity. However, the second iteration is now always performed, for two reasons:
- a second iteration is necessary to implement the new provision from ASCE 7-16 184.108.40.206 that no accidental eccentricity be applied in the absence of torsional irregularity on any level
- the calculation determining the existence of a torsional irregularity is not equivalent to the calculation of Ax despite its similar mathematical form because the displacements used are different according to C220.127.116.11, (see Bug 3521, above).
ii. Recalculation of Ax if ρ = 1.3.
If the program determines that the redundancy factor is 1.3 after being set to 1.0 in the first iteration, it performs and extra design iteration with shear line forces factored by 1.3. It then recalculates the Ax factor and determines torsional irregularities. However, if the Ax factor was determined to be greater than 1.0 on the first iteration, it uses shear lines factored by Ax for the recalculation of Ax and irregularities, when it is supposed to use Ax = 1.0 according to ASCE 7. However, since the calculations depend on relative displacements, and Ax is applied to all shearlines, this problem was unlikely to have much effect.
iii. Ax used for Final Design Check Iteration
If the redundancy factor was 1.0, and the program determined that an Ax factor other than 1.0 needed to be applied, it applied the factor to the shear lines and redesigned the walls. However, after that iteration, it did not recalculate Ax based on the new walls. Therefore, the forces on the shear walls shown in the Design Results are based on an Ax calculated for other walls. The purpose of the final design check is to show the performance of the designed shear walls based on forces that would be generated with those walls, but the forces shown are generated with an Ax using possibly different walls.
iv. Reorganization of Iterations
These changes were implemented in a simplification of the iterations such that Ax, ρ and torsional irregularity is recalculated after each iteration. An initial iteration is performed with accidental eccentricity but Ax = 0, then if ρ = 1.3 another iteration is performed, then another iteration is performed with the recalculated Ax value or the absence of accidental eccentricity, and a final iteration to check the designed walls against a new set of forces generated with those walls. Refer to the Online Help for more information.
e) Intermediate Data for Ax and Irregularity Calculations (Feature 217)
At the end of the Torsional Analysis Details file, there are now tables showing the intermediate data used to determine Ax = (δmax / 1.2 δavg)2 , and the ratio used to determine torsional irregularity = δxe,max / δxe,avg , where δ is the structural displacement and δxe is the story drift, both of them on extreme perimeter shear walls on each level.
These data are shown for each level of the structure, each of the 4 force directions, and for the cases of positive accidental eccentricity and negative accidental eccentricity added to the torsional moment.
The table for Torsional Irregularities shows the shear line forces used to determine perimeter story drift (with Ax = 1.0 and 5% accidental eccentricity), the story drift on the extreme left and right shear lines, the average of the story drifts, and the ratio of maximum drift to average.
The table for Ax shows the structural displacement from the base to the top of each level for the left and right perimeter shearline, the average of the displacements, and the Ax factor.
Each table has notes explaining the meaning of the data and their consequences in the ASCE provisions.
Please note that the data shown are for the Ax and irregularities those used to create the forces shown in the Design Result reports, which create the deflections shown in these reports. If you were to calculate Ax again using these deflections, the value could be slightly different, and if this Ax were used to create new forces the process could be carried on indefinitely.
Testing revealed that his effect is very slight, and no Ax even 1% greater than the previous one was generated when an extra iteration was made.
3. User-Defined Shearline Forces for Rigid Diaphragms (Bug 3528)
User-defined forces entered in Load Input view were being added to shearline forces already derived from rigid diaphragm torsional analysis of applied loads, however such forces used to model the effect of forces from adjoining structures should be included in torsional analysis. As a message appears when Load Input view is invoked giving this as a reason to add these forces, they are now treated as if they were loads on the level on which they are entered and applied to the torsional analysis.
An exception is made when there are no applied or generated loads on the level, only user-applied shear line forces. In this case we can assume that you do not want to perform rigid load distribution and wish to analyze individual shear lines with forces calculated manually.
Furthermore, for all wind and seismic design cases except Directional Method Case 2 wind loads, the force was transferred to the level below only if it was defined for flexible diaphragm analysis as well as rigid. For Directional Method Case 2 wind loads, it was not transferred below at all. This inconsistency has been corrected by this change, and if loads and direct shearline forces are both entered on a level, the effect of the forces is transferred to the level below as if they were loads. If only user-applied shear line forces are added, there is no vertical transfer. Note that flexible diaphragm user-applied forces are still transferred below in all circumstances.
4. Story Weight with Manually Added Building Area Masses (Bug 3537)
Starting with version 11.0, when manual area building masses were added to lines or walls in both the E-W and N-S directions, the story weight wx used to generate seismic loads as per ASCE 12.8-12 was inaccurate in an unpredictable way depending on load length and the tributary width, and could be several times higher or lower than the weight of the input masses. The incorrect weights appeared in the base shear distribution table of the Seismic Load Generation Details and the Seismic Information table of the Design Results.
This problem did not occur when manual masses were entered in just one direction.
In a typical example of a single block of 40 x 40 feet with a gable roof with 25 psf roof self- weight and 3 manually applied 30 psf area building masses with a tributary width of 5 feet, wx was 130,350 lbs when it should have been 62,100 lbs.
Masses are used to generate loads in both directions, so it was possible to model all building masses by adding them to shear lines in just one direction to avoid this problem, however it has been corrected.
5. Large Flexible Shear Line Force Due to Repeated Redundancy Factor (Bug 3527)
For flexible diaphragm analysis, the program was applying the redundancy factor 1.3 from ASCE 7 12.3.4 to shear line forces twice, so that when there was redundancy, the forces were too large by a factor of 1.3. This was happening in both force directions, and whether redundancy was detected by the program or was entered in the Site Dialog. Most buildings do not have a redundancy factor.
6. CAD Drawing Import Procedure (Change 89)
The CAD Import Wizard has been improved to make it easier and more intuitive to add drawings for multiple levels. Previously, it was unclear to some users that you had to press Start positioning to scale the CAD drawing, and the sequence between scaling and adding new levels could be confusing. The Wizard now guides you through a sequence of steps for each level.
7. Simpson Hold-down Database Property Update (Change 115)
The properties of Simpson hold-downs in the database included with Shearwalls have been updated to conform to the 2019-2020 Catalogue. Previously, the properties from the 2015-2016 Catalogue were in use.
The program included an "Impact resistant" check box in the Opening input view, in order that the opening not be included in enclosure calculations from ASCE 7 26.12. This was based on ASCE 7-98 18.104.22.168; however, it was dropped for ASCE 7-05, but the program was not changed.
The Commentary to 6.5.9 says only "operable" windows are to be included in Enclosure calculations, and this is still in C26.12, but was never implemented in the program, so the name of the "Impact resistant" checkbox is now changed to "Non-operable" and has the same effect. .
9. Program Operation
The following problems related to specific user interface operations have been corrected:
a) Crash for Wind Uplift or Dead Loads with Vertical Shearline Offsets (Bug 3518)
The program crashed upon adding dead or wind uplift load to shearlines that had vertical offsets between levels, i.e. a shearline with no walls below it. This has been corrected.
b) Crash when Gypsum Sheathing is Designated OSB (Bug 3519)
In the wall input form, if the OSB checkbox is set for a wood structural panel sheathing side and then the material is set to a gypsum-based material, the program would crash upon running design. This has been corrected.
c) Screen Message upon Change of Gypsum Fastener Length (Bug 3529)
In the Wall Input form, when a fastener length is selected for fiberboard, plaster materials, or gypsum sheathing, and then you make any other action, a message pertaining to Canadian nail sizes appears. It keeps re-appearing, making it impossible to proceed to the design stage. Note that only fiberboard has a choice of fasteners, for the others there was no reason to select the fastener and cause this error to happen. It has been corrected, nonetheless.
d) Crash upon Missing Wall Stud Database File (Bug 3529)
If a wall stud database file used in a Shearwalls project was no longer in your installation or no longer referenced by the database.ini file as being included in the program, the program would show a blank Framing Material in wall input view, and eventually crash upon design if an available material was not selected in its place. The program now outputs a warning and selects an available material if it detects this condition.
Note that an asterisk (*) beside any item in the list of previous releases below indicates that the item was added to the version history record after that version was released.
WoodWorks is releasing a Version 11.2 at the same time as Shearwalls 2019 in order that important corrections and other changes are included in a version that implements the previous design codes and standards.
Most bug fixes and small changes appearing for the first time in Shearwalls 2019 are listed under Version 11.2, below. Please consider both lists as the record of changes for Shearwalls 2019.
1. Update to IBC 2018
The program has been updated to conform to the 2018 International Building Code from the 2015 IBC.
No provisions are taken directly from IBC, but the IBC 2018 references the Special Wind Provisions for Wind and Seismic (SDPWS 2015) and the ASCE 7-16 design loads standard, both of which are implemented in Shearwalls 2019. The load combinations used by Shearwalls that are published in both the IBC and ASCE 7 have not changed.
The references to the edition of the IBC in the Welcome box, Building Codes box, About Shearwalls box, and the Design Results, Seismic Load Generation Details, Wind Load Generation Details, and Torsional Analysis Details output reports have been updated to 2018.
2. Update to ASCE 7-16
The program has been updated to conform to the 2016 ASCE 7 Minimum Design Loads for Buildings and Other Structures from the 2010 ASCE 7.
Refer to B. Update to ASCE 7-16 – Seismic Load Generation and Design (Feature 239) and C. Update to ASCE 7-16 – Wind Load Generation (Feature 239) for the program changes corresponding to changes in design standard provisions.
The references to the edition of the ASCE 7 in the Welcome box, Building Codes box, About Shearwalls box, and the Design Results, Seismic Load Generation Details and Wind Load Generation Details output reports have been updated to ASCE 7-16.
3. Update to NDS 2018
The program has been updated to conform the 2018 National Design Specification for Wood Construction (NDS) and the 2018 NDS Supplement, from the 2015 NDS and Supplement. NDS 2018 is referenced from the 2018 IBC.
The reference to the edition of the NDS in the Building Codes box that is accessed from the Welcome box has been updated to 2018, and the links in the Help menu to the on-line edition of the NDS and Supplement lead to the 2018 editions.
The limited number of procedures in Shearwalls which come directly from the NDS, such as bolt elongation and nail withdrawal, have not changed for the 2018 edition.
Please note that some of the items in this section describe changes to the program that came about because of the analysis of ASCE 7-16 as compared to ASCE 7-10 but were not directly due to changes in the design standard. These items are indicated with an asterisk (*).
These changes pertain to the definition of Site Classes A-F and their use in determining site coefficients Fa and Fv via tables 11.4-2 and 11.4-1, which also depend on the mapped response acceleration parameters Ss and S1, respectively. Fa and Fv are then multiplied by SS and S1 to arrive at spectral response acceleration parameters SMS and SM1, which are then multiplied 2/3 to get design parameters SDS and SD1 , which contribute to the determination of the Seismic Design Category (11.6) , base shear V (12.8), vertical seismic effect (22.214.171.124), min. and max. diaphragm design forces (126.96.36.199), and wall out-of-plane (12.11.1) and anchorage (12.11.2) forces.
a) Change in Standard
i. Min Fa for Default Use of Site Class D
If Site Class D is used as the default site class because soil properties are not known, as per 11.4.3, then a minimum value of 1.2 is now applied to Fa as per 11.4.4. This applies to SS = 1.0, 1.25, or 1.5.
ii. Fa and Fv for Class B when Velocity Measurements not Made
If Site Class B is determined through rock conditions (using Chapter 20 – Site Classification Procedure), but velocity measurements were not made, Fa and Fv are now to be set to 1.0.
iii. Table 11.4-1, Short-Period Site Coefficient Fa
In Table 11.4-1 for Fa,
- The last column was for Ss greater than or equal to 1.25, but now a new column has been added for Ss greater than or equal to 1.5
- The values for Site class B have all been reduced from 1.0 to 0.9
- The values for Site class C have increased 0.1, except for Ss = 1.25 which has increased 0.2
- The values for Site class E have increased 0.1 for SS <= 0.25 and SS = 0.75
- No values are provided for Class E for SS = 1.0 or greater (3 columns), as section 11.4.8 now says that site-specific analysis is required for them. Refer to 2.a)iii below for an exception to this and the values used in that case.
iv. Table 11.4-2, Long-Period Site Coefficient Fv
The last column was for S1 greater than or equal to 0.5, but now a new column has been added for S1 greater than or equal to 0.6
- The values for Site class B have all been reduced from 1.0 to 0.8
- All values for Site class C except for S1 = 0.3 have decreased by 0.1 or 0.2.
- All values for Site class D except for S1 <= 0.1 have increased by 0.2 or 0.3.
- For all Class D except for S1 <= 0.1 (5 columns), a note a refers to 11.4.8 for conditions under which ground motion analysis must be done instead of using the tabulated value. Refer to 2.a)iv below.
- No values were provided for Class E for S1 = 0.2 or greater (5 columns), as section 11.4.8 says that site specific analysis is required for them. However, refer to 2.a)v below for an exception to this and the values used for that exception.
- The sole remaining value for Site class E, S1 <= 0.1, has increased from 3.5 to 4.2.
b) Min Fa for Default Use of Site Class D
A checkbox has been added to the Site Information dialog called Chosen by default. It is active for Site Class D, only and is unchecked by default. If checked, the site coefficients for SS = 1.0, 1.25, or 1.5 are set to 1.2.
As it is now possible to use site-specific procedures and enter your own Fa for class D (see 2.c) below), the program will not restrict Fa to 1.0 if you do so. It is possible that ground motions are determined rigorously but soil profiles are not.
c) Fa and Fv for Class B when Velocity Measurements not Made
A checkbox has been added to the Site Information dialog called No velocity measurements. It is active for Site Class B, only and is unchecked by default. If checked, the program will set Fa and Fv to one.
As it is now possible to use site-specific procedures and enter your own Fa and Fv for class B (see 2.c) below), the program will not restrict Fa and Fv to 1.0 if you do so, as it is possible that velocity measurements are not taken but 21.2 Risk-targeted Hazard Analysis is used for Fa and Fv.
d) Table 11.4-1, Short-Period Site Coefficient Fa
Table 11.4-1 values have been modified to those in ASCE 7-16. A new column for SS greater than or equal to 1.5 has been added and the table interpolation modified accordingly.
For site class E and SS greater than 0.75, the input of Fa in the Site dialog is active, as described in 2.c)i below . Note that this starts at 0.75 rather than 1.0 because interpolation is not possible between 0.75 and 1.0 with no tabulated value for 1.0.
e) Table 11.4-2, Long-Period Site Coefficient Fv
Table 11.4-2 values have been modified to those in ASCE 7-16. A new column for S1 greater than or equal to 0.6 has been added and the table interpolation modified accordingly.
For site class E and S1 greater than 0.2, the values shown in the Fv input are given in 2.a)v below, and the operation of this input is described 2.f) below. .
Refer to 2.e) below input of values when ground motion analysis must be done for class D as per note a.
This section pertains to the conditions under which site-specific ground motion analysis must be done to determine the site coefficients Fa and Fv rather than using the tabulated values described in item 1 above. Note that for both ASCE 7-10 and ASCE 7-16, using ground motion analysis is permitted for any structure, but Shearwalls only allowed it when it was required.
a) Change in Standard
i. Required Site-specific Procedures for Site F
For site F, the reference to site-specific ground motion procedures in 21.0 has been changed site response analysis in 21.1 (as opposed to also including ground motion hazard analysis in 21.2).
ii. Cases Requiring Ground Motion Analysis
The following cases now require ground motion hazard analysis from 21.2 rather than using the tabulated values of Fa and Fv.
Seismically Isolated or Damped Structures (S1 >= 0.6)
Seismically isolated or damped structures with S1 greater than or equal to 0.6. This requirement was also in ASCE 7-10.
Class E, Ss >= 1.0
This clause says that the analysis is required for Ss => 1.0, but because there is no value for Fa for Ss = 1.0 for interpolation, it is needed for Ss > 0.75, unless Exception 1 (below) is used. Previously ground motion analysis was not required for Class E.
Class D, S1 >= 0.2
For site class D, the analysis is required for Fv if S1 >= 0.2 unless the Exception 2 (below) is used. Previously ground motion analysis was not required for Class D.
Class E, S1 >= 0.2
For site class E, the analysis is required for Fv if S1 >= 0.2 unless the Exception 3 (below) is used. Previously ground motion analysis was not required for Class E.
For Class E, Class C coefficients can be used in lieu of ground motion hazard analysis.
The following conditions apply when Site Class D is used with S1=> 0.2 to avoid site specific analysis:
- For T <= 1.5 TS, the seismic response coefficient CS must be calculated with 12.8-2, with TS defined as SD1/SDS. , As 12.8-2 is the usual procedure, presumably this means that the maximum CS from 12.8-3 cannot be applied. Maximum Cs is only used when T >= Ts, so that this applies in the range T = TS to 1.5 TS. This range is within the range of structures possible in Shearwalls, but not commonly encountered, so that ordinarily, tabulated values will be used with Cs from 12.8-2 that is below the maximum.
- For TL >=T > 1.5TS, 1.5 times the maximum CS given in Eq’n 12.8.3 must be used. This range is at about the limit of what can occur in Shearwalls but could be more likely to happen in some locations.
- For T > TL, 1.5 times the maximum Cs given in Eq’n 12.8.4 must be used. TL is the long-term period given in maps 22.14-17. The lowest period in these maps is 4s, far beyond what is encountered in Shearwalls, so this range does not apply.
If Site Class E is used with S1 => 0.2, you can avoid site specific analysis for if the period T is less than or equal to TS, which it ordinarily is in Shearwalls. The ASCE 7-16 does not include tabulated values for S1 and Class E, but ASCE provided us with coefficients to use that will appear in the next ASCE supplement. They are Fv (0.2) = 3.3, Fv (0.3) = 2.8, Fv (0.4) = 2.4, Fv (0.5) = 2.2, Fv (0.6) = 2.0.
b) Site Class F
When Site Class F is chosen:
i. Required Site-specific Procedures*
At the bottom of the Site Information section of the Seismic Load Generation Details file, a note now appears saying that site response analysis from 21.1 is needed.
ii. Default Values*
When Class F is selected in the Site Information dialog, the default value is no longer what was in the previous entry for the other site classes; instead the program places 0.0 in the input. If it is not changed, you are prompted to enter a value.
Shearwalls now allows you to override the tabulated values for Fa and for Fv for the permitted use of coefficients from ground motion analysis on any structure, or their required use on seismically isolated or damped structures.
Two checkboxes called Use site-specific ground motion procedures in the Site Information dialog allow you to override the tabulated values for Fa and for Fv
For Site Class F, they are always inactive and checked, and the Fa and Fv boxes are active, as is currently the case.
For Site Classes A-E, the checkboxes are active and unchecked by default, and Fa and Fv are inactive. If they are checked, then the Fa and Fv values become active and show values from the Tables 11.4-1 and 11.4-2, and you may modify these values.
If ground motion analysis was not required for Fa and/or Fv according to 11.4.8, but you decided to use it for either or both, a note appears under the Site Information section of the Seismic Load Generation Details indicating site-specific ground motion hazard analysis from ASCE 21.2 was used.
If ground motion analysis was required for Fa and/or Fv unless the Exceptions 1-3 are invoked, and you decided to forego the Exceptions and enter an Fa and/or Fv, the same note appears except that it says the analysis is “required” rather than “used”.
d) Seismically Isolated or Damped Structures with S1 >= 0.6
No changes were made specifically to implement seismically isolated or damped structures with S1 >= 0.6. If you have such a structure, then you check the Use site-specific ground motion procedures box for Fv and enter the result of your site-specific analysis.
e) Exception 1 for Ss and Class E
To implement Exception 1, the value in the Fa input for Class E for Ss > 0.75 is set to that for Class C. This can be over-ridden by selecting the checkbox for site specific analysis and entering a different value.
For site class D and S1 >= 0.2, if the site-specific ground motion checkbox is unchecked upon load generation, for each direction:
- if Ts < T < = 1.5 Ts, the program does not apply the maximum CS from Eqn. 12.8-3 when determining base shear V, always using Eqn. 12.8-2. The value shown as the maximum value in the Seismic Load Generation Details table is from 12.8-2.
- if T > 1.5 Ts, the program will apply 1.5 times the maximum CS rather than the calculated maximum when determining base shear V. The calculated and maximum values from Eqns. 12.8-2 and 12.8-3 are still shown in the table, and the Cs value shown is 1.5 times the maximum value.
Notes appear below the table in the Seismic Load Generation Details indicating that the exception was applied in the direction or directions, and that max CS was not applied for T <= 1.5 Ts, or that 1.5 max CS was applied for T>1.5Ts
For site class E and S1 >= 0.2 the values shown in Fv are those supplied by ASCE (see 2.a)v below), If T > Ts, then the site-specific ground motion checkbox is always checked and disabled, and you must enter Fv as per Exception 3.
3. Application of Redundancy Factor (188.8.131.52)
a) Change in Standard
184.108.40.206 now refers to the minimum and maximum diaphragm forces from Eqns. 12.10-2 and 12.10-3 when listing all those design provisions for which redundancy factor ρ = 1. Previously it referred only the diaphragm force Fpx from Eqn. 12.10-1
b) Drag Strut Force Calculation
The only application of Fpx in Shearwalls is for drag strut forces, and the program was already setting ρ = 1 when evaluating Eqns. 12.10-2 and 12.10-3 for them. However, the following small inaccuracies in the Design Results were noticed and corrected:
i. Seismic Information Table Note*
In reference to the application of the redundancy factor under the Seismic Information table now refers to the diaphragm force Fpx as well as the drag strut forces.
This is because drag strut forces can be based on the design shear force factored by ρ if it is greater than the diaphragm force, according to 12.10.2 and 220.127.116.11.
ii. Drag Strut Table Legend*
In the drag strut table legend, the phrase
Includes redundancy factor rho.
has been removed from the definition of shearline force for perforated walls.
4. Maximum SDS Value in the Determination of Cs and Ev (18.104.22.168)
a) Change in Standard
i. Limit on SDS v. SS
Previously, the value of SS, the short-term mapped seismic response acceleration parameter, was permitted to be limited to 1.5 for certain design procedures and under certain conditions. Now there is a limit on SDS, the short-term design response acceleration parameter, of the greater of 1.0 and 0.7 times the calculated SDS. As these parameters are related by SDS = 2/3 Fa Ss, the old limitation was equivalent to SDS <= Fa, so this represents a substantive change.
According to the values of Fa in Table 11.4-1, SDS is greater than 1.0 for Site Class C and SS >= 1.25, and for Site Class D with SS greater than 1.5. These are common Site Classes, and SS can be as high as 2.0 in earthquake- prone regions of the USA. This limitation will come into play in many circumstances.
ii. Relevant Applications of SDS
Previously this limitation was applied to the calculation of seismic response coefficient CS in Eqn. 12.8-2 and its lower limit in 12.8-3. CS is multiplied by the building weight to arrive at base shear V.
It is still applied in these places, but now also to the calculation of SDS for vertical earthquake load determination in Eqn. 12.4-4a, which is Ev = 0.2 SDS D, where D is dead load.
The limit on the value of SDS is still not applied to the Seismic Design Category (11.6), min. and max. diaphragm design forces (22.214.171.124), and wall out-of-plane (12.11.1) and anchorage (12.11.2) forces. In addition, it is not applied to SDS in the calculation of TS for the new Exception 2 to the use of site-specific ground motion analysis for Site Class D (11.4.8).
iii. Acceptable Criteria
The following criteria to be met for use of this limit were in ASCE 7-10 and are still to be applied:
- Building is 5 storeys or less
- Building has a fundamental period, T = 0.5 s or less
The following criteria are new to ASCE 7-16
- No irregularities
- Site Class A-D (not E or F)
- Redundancy factor is 1.0 (not 1.3)
- Risk category I and II
b) Value of Limit on SDS vs. SS for Calculation of CS
The program now applies a limit of the greater of 1.0 and 0.7 times the calculated SDS to the value of SDS used for CS = SDS / (R/Ie), and to the lower limit CS = 0.044 SDS Ie. Previously, the SS value in determining SDS was limited to 1.5.
c) Application to Ev
The limit now applies to the SDS calculation of the vertical seismic force component of hold-down forces, Ev = 0.2 SDS D
i. Effect of New Criteria
As the building can be irregular or have a redundancy factor in one direction but not the other, the limit can be applied to hold-downs in one force direction but not the other.
As it can be torsionally irregular for rigid diaphragms but not flexible, the limit can be applied for flexible diaphragms but not rigid.
ii. Plan View Legend
In the Plan View legend explaining the Ev force, the SDS shown is now the limited one, and the program now shows SDS values for both force directions in the unusual case that they are different. This can now be different for rigid and flexible diaphragm design.
iii. Seismic Information Table
In the note under the Seismic Information table of the Design Results explaining the Ev force, the SDS shown is now the limited one, and the program now separate notes for both force directions in the unusual case that they are different. This can now be different for rigid and flexible diaphragm design.
d) Implementation of Acceptable Criteria
i. Risk Category
The limit on SDS is no longer applied to buildings in Risk Category III (Hazardous) or Risk Category III (Essential).
ii. Site Class
The limit on SDS is no longer applied to buildings in Site Classes E and F.
As seismic load generation is performed before shear walls are designed and irregularities can be detected, the program relies on the new user input of irregularities in the Site Information dialog (see D below) to determine whether the structure limit cannot be applied because the structure is irregular. If you are performing both rigid diaphragm design , if any irregularity is entered, the limit on SDS is suppressed. If only flexible diaphragm design is set to be performed, it is suppressed for any irregularity except horizontal Torsional irregularities 1a and 1b.
As the program is able to detect torsional irregularities and Horizontal Irregularity 4 – Out-Of Plane Offset, if during shear wall design these irregularities are detected but hadn’t been entered in the Site Information, or vice-versa, and if the SDS value used for CS would have been different as a result, a message appears suggesting that you reset the irregularity selections and rerun the load generation and design.
If the only irregularity set in the Site information is a torsional irregularity, and a limit that would have been imposed on SDS is suppressed, a message appears suggesting that you run load generation and design on rigid and flexible diaphragms separately. This allows the limit on SDS to be applied for flexible diaphragm design while using the calculated SDS for rigid diaphragm design.
iv. Redundancy Factor ρ
For the purpose of calculating Cs for base shear V, the limit on SDS is applied if 1.0 or Calculate is set in the Site Information dialog for the Redundancy Factor ρ. For the purpose of the vertical seismic component Ev of hold-down forces the limit is applied if ρ is set to 1.0 or the program calculates ρ = 1.0 for the force direction.
If Calculate was set and ρ = 1.3 was calculated by the program, a message appears suggesting you set ρ to 1.3 and regenerate loads. If this happens only for rigid or for flexible diaphragm design, the message suggests running load generation and design for these cases separately.
In the Seismic Load Generation Details output, in the note referring to the applicability of the two SDS values shown,
i. References to Ss and Ev
The note no longer refers to SS and includes Ev among the calculations that are limited.
ii. Non-limited Applications*
The note now also includes diaphragm design force limits and out-of-plane forces those design procedures that are not limited. Previously it mentioned only the Seismic Design Category.
a) Change in Standard
The requirement that an accidental torsion of 5% of the building width be added to torsional analysis for rigid diaphragms has been limited to structures of Seismic Design Category B with Type 1b horizontal structural irregularity (Extreme Torsional) and SDC C-F with either Type 1a (Torsional) or Type 1b. The irregularities are defined in Table 12.3-1.
The calculation of Type 1a or Type 1b horizontal irregularities requires evaluation of the deflection at extreme shearlines derived from forces using the 5% accidental eccentricities and amplification factor Ax = 1.0. Ax is from 126.96.36.199
b) Torsional Analysis
The program already did a preliminary iteration of loads analysis and design to determine the value of redundancy factor ρ and the torsional amplification factor Ax . In that iteration the program now determines the torsional horizontal structural irregularities 1a and 1b using Ax = 1.0 Torsional irregularity 1a occurs for Ax > 1.0, and 1b occurs for Ax > (1.4/1.2)2, or equivalently when δmax / δavg is greater than 1.2 or 1.4, respectively, δmax being the largest and δavg the average of the story drifts at the endmost shear lines.
The 5% accidental eccentricity is not applied for SDC A, is applied only if there is an extreme torsional irregularity for SDC B, and only if there is a torsional irregularity for all other structures.
In the Torsional Analysis Details file, if there is no accidental eccentricity:
- The line giving the value of accidental eccentricities eax and eay is removed
- The line giving the Torsions T does not show eax or eay being added and subtracted
The note that gave the reference to 188.8.131.52 now gives the SDC and presence or absence of torsional irregularities 1a and 1b, and if applicable indicates that it is 0 for those reasons.
The amplification factor Ax, which was only shown if greater than 1.0, is now always shown. If it is 1.0, it still does not appear in the line showing the calculation of torsion T.
a) Change in Standard
i. Definition of Transfer Force
The description of forces being transferred through the diaphragm via offsets or stiffness changes in shear walls has been formalized in 11.2 Definitions as a Transfer force, rather than being more briefly described in 184.108.40.206 Diaphragm Design Forces.
ii. Overstrength Factor for Transfer Forces
There is now a requirement that the transfer forces from discontinuous shearlines be increased by the overstrength factor Ω0 from 220.127.116.11 before being added to the diaphragm force.
iii. Redundancy Factor
The requirement that the redundancy factor ρ from 12.3.4 be applied to transfer forces from discontinuous has been removed. This is in accordance with items 5 and 6 in the list of conditions in 18.104.22.168 for which ρ = 1, which refer to the design of members, collector elements, connections, etc. where overstrength factor is either required or used.
Note that this is in seeming contradiction with the Commentary C22.214.171.124 which says that the redundancy factor applies to diaphragm transfer forces, but in a communication ASCE clarified that ρ and Ω0 are not to be applied simultaneously and that the Commentary applied to typically smaller transfer forces due to changes in lateral stiffness rather than Irregularity Type 4 Offsets to which Ω0 is applied.
iv. Exception for One-and Two-family Dwellings
An exception has been added indicating that for one- and two-family dwellings, the Ω = 1.0 so that overstrength is not required on transfer forces.
b) Transfer Forces
The transfer forces due to vertically discontinuous shearlines that are used for calculation of shearline forces on the level below for the purpose of drag strut force calculation have been changed as follows:
If the shearline forces from above include a redundancy factor ρ = 1.3, it is removed. The overstrength (Ω0) factor of 3.0 for bearing wall systems and 2.5 for building frame systems (from Table 12.2-1) is applied. For flexible diaphragm design, both
c) Shearline Forces for Drag Strut Design based on Diaphragm Force*
The requirement that transfer forces from discontinuous shearlines be factored for overstrength inspired a re-evaluation and reimplementation of the calculation of shearline forces used to create drag strut forces when they are based on the diaphragm design force Fpx.
i. Previous Implementation
Previously, the program determined a proportionality ratio between the diaphragm force Fpx, and the sum of the unfactored design force Fx on all levels above and including the level in question. It then multiplied each ASD-factored shearline force on that level by that factor, to convert from base-shear-based forces to Fpx-based forces. This approach was an approximate one in the following ways:
Discontinuous transfer forces
Such an approach treats discontinuous transfer forces as if they were a load due to the equivalent amount of building mass at that location, and that load is based on the diaphragm design force Fpx rather than the design shearline design force Fx.
This approach incorporated the redundancy factor ρ, as was required by 126.96.36.199, only indirectly via its contribution to the design shearline forces that are then factored by the proportionality ratio, so that the redundancy factor was effectively modified by that ratio. The much larger Ω0 factor would make this an unacceptably large discrepancy.
User-applied Loads and Forces
Manually entered seismic loads and shearline forces were not considered in this calculation, and if they exist, they would be assumed to be based on Fpx rather than the base shear. As these may represent forces from adjoining structures, this may not have been the best approach.
Rigid Diaphragm Analysis
The assumption of a linear proportionality factor relating diaphragm-force-based shearline forces and base-shear-based forces does not consider torsional effects and non-linear stiffness calculations used in rigid diaphragm analysis. That is, for rigid diaphragms, a larger diaphragm-based force might cause a shift in distribution of forces to the shearlines that is not considered.
ii. New Implementation
A proportionality factor between the diaphragm force Fpx and the unfactored design force Fx on the level in question is now applied to all the seismic loads that were created from building masses on the level x. The program then gathers these loads along with transfer forces from the level above, factored by Ω0, and user-applied loads and forces, and distributes them to the shearlines via rigid and flexible diaphragm distribution routines.
This shearline force represents the contribution of the loads on the level with the drag strut. The shearline forces from levels above on the same shearline are then added in (see 7.b) below), and then the maximum of this force and the force used for shear wall design is used for drag strut force calculations.
Note that the resulting drag strut design shearline forces on the level below are now included in the Design Results output (7.d) below) and shown in Plan View (see E.6 below).
d) Diaphragm Loads and Force in Plan View*
It is now possible to view the elemental loads and forces associated with the diaphragm force Fpx and the transfer forces used with Fpx in the Loads and Forces action of Plan View. Refer to E.6 below for details.
e) Exception for One-and Two-family Dwellings
The exception for one- and two-family dwellings has not been implemented in Shearwalls.
The following pertains to the output of the diaphragm force on each level and in each direction in the Seismic Information table of the Design Results output.
i. Total Diaphragm Force
The table has been modified to show two forces for each direction, one derived from Fpx from 188.8.131.52, and the other the total force including transfer forces and any seismic forces you enter directly (as opposed to generating with building masses).
ii. Factored Force
Previously the diaphragm force Fpx shown was unfactored, but as the transfer forces are factored, it was decided to show the ASD-factored diaphragm forces.
The table legend explains that
- The forces are ASD-factored
- Fpx is from Eqns. 12.10-1, -2, and -3 (not just 12.10-1)
- Transfer forces include overstrength, with the value of Ω0 and reference to Table 12.2-1
- Total = Fpx + transfer forces
a) Change in Standard
ASCE 7-16 has dropped an Exception 1 in 184.108.40.206, allowing the collector forces to be limited to those derived from the maximum diaphragm force, 12.10-3. However, this does not affect Shearwalls, which uses the other exception that refers to all 220.127.116.11, which includes 12.10-3.
Because 18.104.22.168 refers only to transfer forces from discontinuous shearlines, it was thought that forces from continuous shearlines above the level with the collector were not to be included in the “seismic forces originating in other parts of the structure” referred to in 12.10.2. However, in a communication, ASCE clarified that they were to be included, so now Shearwalls adds the design shearline forces (based on base shear) from shearlines on the upper levels, to the shearline force based on diaphragm design force Fpx.
Because Fpx -based forces are given as a minimum force in 22.214.171.124., the larger of the base-shear-based shearline force and the Fpx -based shearline force is used for drag strut force calculations. Previously the larger of the design shear force and the Fpx -based force without upper levels was used, making it much less likely that Fpx -based forces would govern.
c) Seismic Design Category B*
Because there is no explicit guidance on Seismic Design Category B, 126.96.36.199, which mandates use of the Fpx -based force as a minimum force for collector for SDC C-F, was applied to SDC B as well. This is no longer the case, and the base-shear based design shearline forces are used for SDC B with no minimum Fpx -based force applied.
i. Shearline Force*
In the Collector Forces table of the Design Results (previously called Drag Strut Forces), for each shearline, the shearline force used to create the drag strut force is now shown.
The legend entry for Drag strut Force in the Collector Forces table of the Design Results has been modified to indicate:
- That only for SDC C-F is it the greater of the design shear force and the Fpx-based force used
- Forces from discontinuous shearlines are added in, and factored for overstrength by Ω0
- Shearline forces from story above added
- To refer to the Seismic Information Table for diaphragm force and Ω0
a) Change in Standard
12.11.1 for out-of-plane wall forces and 188.8.131.52 for wall anchorages have been reorganised and rephrased to remove the ambiguity that suggested both sections referred to anchorages. 12.1.1 now refers to wall forces only.
The only substantive change within the reorganization is that there is now a minimum force of 0.2 Wp to be applied to the wall, where Wp is the weight of the wall tributary to the diaphragm.
b) Calculation of Anchorage Force
The anchorage force is now taken as 0.2 Wp for those cases that 0.4 SDS Ie ka < 0.2, where ka is the flexible diaphragm amplification factor defined in 184.108.40.206.
a) Change in Standard
A ground elevation factor Ke has been added to account for the effect of altitude on velocity pressure qz in equation 26.10-1 (Section 26.10.2). Ke is determined from Table 26.9-1 or the equation in Note 2 to that table. The equation
Ke = e-0.000119zg
with zg in meters, is based on the formula for change in pressure p or density ρ with altitude z,
p/p0 = ρ/ρ0 = e -gz/RT
g is acceleration due to gravity, R the gas constant of air, and T is temperature in Kelvin = 288 degrees.
Previously a procedure in C27.3.2 was used to modify the factor 0.0256 in the equation for qz for the change of air density with altitude. The density was taken from a table, and the factor is just ρg in the expression p = ρgv2 for velocity pressure. Now the sea level factor 0.0256 is always used and then modified by the Ke factor.
Note that the concept of minimum, average and maximum density based on factors such as temperature, weather, season and latitude has been dropped and the new formula is based on density at 15 degrees C. Note too that the densities shown in ASCE 7-16 Table C26.9-1 do not correspond exactly to any of the minimum, maximum, or average densities from 7-10 C27.3-2, so this is a substantive change to the calculation of velocity pressure in all cases other than sea level pressures.
The data group Velocity pressure coefficient (C27.3.2) in the Site Information dialog has been renamed Ground elevation factor Ke.
The input of the air density category (minimum, average, maximum) and ambient air density, and the display of resulting mass density constant, have been removed. The Altitude input has been retained, and the resulting Ke factor is shown.
The calculation of the mass density constant has been removed and it is now always 0.0256. The Ke factor is calculated using the equation in Note 2 of Table 26.9-1 and applied to the velocity pressure qz in equation 26.10-1.
In the Wind Load Generation Details,
Ke has been added to the Definitions, as has ground elevation zg. The definition for what we called d, the mass density constant, has been removed.
Ke has been added to the equation for q, which has also been changed to show the number 0.0256 instead of the symbol d for air density. The equation for Ke has been added and the one for d removed.
The value calculated for Ke has been added to the Data (all loads) section.
a) Change in Standard
A Partially Open category has been added for those buildings that are not Open, Enclosed, or Partially Enclosed. Previously Enclosed buildings were defined as not Open or Partially Enclosed, but now they are defined by having opening area in each wall less than the lesser of 4 sq. ft. or 1% of the wall area.
The internal pressure co-efficients GCpi for Partially Open walls are the same as for Enclosed, +0.18 and -0.18, so this change does not impact pressures generated.
In the Site Dialog, Partially open has been added to the list of Enclosure choices. The wording Partly Enclosed has changed to Partially enclosed.
These changes are also reflected in the Site Information section of the Wind Load Generation Details.
c) Enclosure Estimation
The program applies the new rules to the estimation of enclosure classification that is triggered by a button in the Site dialog. Note that a “wall” is taken by Shearwalls to mean an entire building face.
d) Load Generation
Internal pressure GCpi coefficients 0.18 and -0.18 are applied to the Partially Open walls when selected.
A limit has been added to the end zone width a for low-rise structures greater than 300 m in each dimension, with roof slopes less than 7 degrees. For these structures a is limited to 0.8 times the mean roof height h.
This limit is applied to those structures designed using the Envelope Procedure. The ordinary end zone width is defined as
a = max (min (.1 D, 0.4h), max ( 0.4D, 3ft) ).
where D is the least horizontal dimension of the building. For buildings whose least horizontal direction is greater than 300 ft, this is now
a = min (max ( min (.1 D, 0.4h), max ( 0.4D, 3ft) ), 0.8h).
End zones defined for the Envelope Procedure for MWFRS loads in Fig 28.3-1 have elevated pressure coefficients relative to the rest of the building face, and for C&C wall loads defined in Fig 30.3-1 have elevated coefficients for negative pressures (suction).
Note that there are few wood buildings with both dimensions greater than 300 ft.
Shearwalls now allows you to designate walls as Force transfer walls. These walls allow for light gauge steel straps to transfer tensile forces around openings, and blocking to transfer compressive forces, so that the sheathing above and below the opening contributes to shear wall resistance.
Design of the force transfer walls in Shearwalls follows what is known as the Diekmann method, as presented in APA T555, Design for Force Transfer Around Openings (FTAO). The program also conforms to Special Design Provisions for Wind and Seismic (SDPWS) 220.127.116.11 and 18.104.22.168.
In the Diekmann method, shear forces are developed in each wall “pier”, defined by the rectangular areas:
- between an opening and the top or bottom of the wall (opening pier)
- between two openings or an opening and the end of the wall (central pier),
- between a central pier and the top or bottom of the wall. (corner pier)
A central pier is defined by the top of the highest opening and the bottom of the lowest one.
Force transfer walls are subject to the following limitations:
a) Opening Configuration
There must be least one foot of sheathing above and below each opening, to allow shear forces to develop in opening piers. A consequence is that walls with doors cannot be designed as force transfer walls. One solution to this situation is to create a non-shearwall for the door.
b) Height-to-Width Ratio
As per SDPWS 22.214.171.124 and 126.96.36.199., each central pier (i.e. between openings or between opening and wall end) must conform to the height-to-width limitations given in Table 4.3.4, that is, 3.5:1 for blocked walls and 2:1 for unblocked walls.
c) Pier length
As per SDWPS 188.8.131.52.(1), the length of the wall piers (distance between openings or distance between an opening and the wall end), must be 2’ or greater. According to advice we received from FTAO researchers, this limitation has been applied to unblocked walls only; for blocked walls the piers must be 18” or longer.
d) Full-height End Segments
As per SDWPS 184.108.40.206.(2), a full height segment must be at each end of the wall, that is, a force-transfer wall cannot start at an opening.
e) Gypsum Materials
Gypsum wallboard or plaster sheathing materials are not compatible with force transfer walls. If such materials exist on a force transfer wall, they are ignored for both design and deflection calculations.
2. Other Considerations
Shearwalls does not consider all the force-transfer details required to ensure that the assumptions of the Diekmann method are satisfied. The designer is responsible for verifying the strength of all elements and connections in the load path using sound engineering judgement. In particular:
a) Width-to-Height Ratios
SDPWS provides only height-to-width limitations, and in ordinary shear wall segments, width-to-height is rarely an issue. However, for force-transfer walls, narrow piers above openings can have very high width-to-height ratios such that they cannot be relied upon to transfer shear forces. For example, using our 1-foot pier height limitation, a 4-foot opening exceeds the 3.5:1 width-to-height ratio.
In the absence of design code guidance, Shearwalls does not check pier width-to-height and leaves the design of openings to your judgement in this regard.
When sheathing is configured such that panels wrap around the openings in a C- or L-shape with no seam between the corner pier and the opening pier or central pier, shear is transferred through the sheathing rather than via the straps and blocking, and the assumptions of the Diekmann method are not valid. Tests have shown extremely large differences between actual forces and those computed by force-transfer analysis in this case.
Shearwalls does not consider sheathing layout details (other than whether the panels are applied vertically or horizontally). It is the responsibility of the designer to ensure seams exist on the studs at the sides of opening segments or on the force transfer blocking so that force is transferred through blocking and straps rather than sheathing.
3. Continuous Force Transfer Strap Setting
A setting called Continuous strap across entire wall has been added to the Design Settings. If checked, it is assumed that the force transfer straps and blocking extend in one straight line across the entire wall, so that all central piers extend from the top of the highest opening on the entire wall to the bottom of the lowest opening on the wall. The opening piers and corner piers are also measured from the top of the highest opening and bottom of the lowest opening, so that some sheathing may be contained within the opening area that does not resist shear force.
If unchecked, it is assumed that strapping and blocking exist at the top and bottom of each opening and extend far enough into the adjacent segments to transfer shear force to the central piers. In this case, the central piers extend from the top of the highest of the two adjacent openings, to the bottom of the lowest of the adjacent openings. The opening piers are measured from the top and bottom of each opening.
The use of non-continuous straps does not provide an advantage in terms of shear forces developed as the force developed in the core of the central pier is the same in either case. Strap/blocking forces may be lower; but more strapping and blocking are required due to overlap. The use of this option is recommended only to avoid large strap forces, or if it is more convenient to construct the wall with blocking at the top and bottom of openings.
a) Wall Input View
A wall type called Force-transfer has been added to the list of wall Types in wall input. Walls of this type that have openings are displayed with square hatching, to distinguish them from perforated walls (diagonal hatching) and segmented walls (solid). A legend item has been added to show the force transfer hatching.
Force transfer walls without openings appear in solid colour.
The limitations on force-transfer wall geometry are imposed when you change the wall’s geometry in any way, i.e. via lengthening, shortening, changing the height, adding or removing openings, or changing opening dimensions. If this causes segments that are too narrow, piers with disallowed height-to-width ratios, or openings that are too close to the top or bottom of the wall, a warning is issued and the wall configuration is reverted to what it was before the change.
If an existing segmented or perforated wall, or non-shearwall, is changed to a force-transfer wall, the program checks the limitations and if any one is violated, a message is issued, and the change is reverted.
c) Standard Wall
A standard wall called Exterior Force-transfer has been added to the list of standard walls that appear when you first run Shearwalls or select Reset original standard walls from the Default settings.
d) Walls with No Openings
Walls designated as Force-transfer walls but have not yet had an opening placed in the wall, are in every respect treated by the program as segmented walls.
Shear force distribution to the piers in force-transfer walls is described in APA T555 as a sequence of numerical calculations in a design example of a wall with 2 openings of the same size. The following gives an algebraic formulation of the general procedure used by Shearwalls; it corresponds to the calculations in the T555 example.
The following symbols are used in the shear force distribution equations:
V – Total shear force on wall (lbs)
The total shear force in a vertical line on the wall is equal to the hold-down force VH / L (neglecting hold-down offsets), so the unit shear force in the upper and lower piers is that force divided by the length of the combined height of the piers:
The force in the central piers is:
This is the unit diaphragm shear force over the segment with the central pier plus the portion of diaphragm shear force over the openings on either side of the pier transferred to the pier via straps and blocking. This portion is determined by multiplying the unit diaphragm force by the ratio of the adjacent opening lengths to the combined length of the central piers on either side of these openings.
d) Corner Piers
The unit force in the corner pier is the unit force in the central pier minus the strap/blocking forces from each side divided by the length of the pier.
The strap/blocking forces are the total force (not a unit force) above and below the opening apportioned to the left and right side by the proportion of total length of the piers on each side.
Walls designated as force-transfer without openings are treated as segmented walls.
a) Aspect Ratio Factor
Although it isn’t explicitly stated in SDPWS 220.127.116.11, we were informed that the intention of the SDPWS is that force-transfer wall central piers that have height-to-width ratios between 2.0 and 3.5 are subject to the Aspect Ratio Factor given in 18.104.22.168 (for deflection-based distribution to segments), and the adjustments in the Exceptions to 22.214.171.124.1 ( for capacity-based distribution).
These are the same factors and adjustments used for segmented wall full-height segments, except that for force-transfer walls they applied to the dimensions of the central piers between two openings or between an opening and the wall end.
b) Critical Design Shear Force
The program determines the critical case of pier force / Aspect Ratio Factor for any pier in the wall (including corner and opening piers with a factor of 1.0) and designs the wall for that case.
c) Gypsum Materials
The contribution of gypsum wallboard and plaster materials is ignored in calculating design strength of force-transfer walls, regardless of what is set in the Ignore contribution of... Design setting.
7. Hold-downs and Hold-down Forces
Force-transfer walls require hold-down devices only at wall ends, so that hold-down forces in Shearwalls are at the ends of force-transfer walls and there is no hold-down at the sides of each opening.
a) Input and Output
Hold-down devices are input only at the ends of entire walls, as for perforated walls. Hold-down forces are reported in Plan View, Elevation View, and the Hold-down Design table only at the end of walls.
b) Force Calculation
The shear force used for overturning calculations is the shear force applied to the entire wall. Dead and wind uplift loads over the entire length of the wall are distributed to the hold-downs at the end of the wall, so the hold-down force calculations include the dead and wind uplift loads over openings, instead of distributing them to opening supports.
c) Axial Wall Stud Forces
The unit shear forces in the piers that are shown acting horizontally also act vertically along the studs at wall and opening ends. The vertical forces at the wall end add up to the hold-down force, neglecting the hold-down offset.
Beside the openings, tension and compression axial forces are developed in the studs due to the difference in shear force in piers adjacent to the studs. Shearwalls does not calculate or report these forces, but they should be considered when designing the wall.
The procedure for calculating deflection of force transfer walls comes from APA T555, Design for Force Transfer Around Openings (FTAO). This applies only to force transfer walls with openings; those without are treated as segmented walls.
a) Reduced Segment Height
In this method, the deflection due to the shear force in the central pier is calculated on each wall segment between openings, but assuming that the height of all but one of the segments is the height of the central pier plus the top pier only, i.e., the bottom pier is ignored. The one segment that is still considered to be full height is at the far end of the wall from the force direction.
b) Averaging of Segment Deflections
This analysis is done in both force directions using the same wall shear force, then all the deflections from the segments in each direction are averaged to arrive at the deflection of the entire wall; i.e. if there are n segments, 2n segment deflections are averaged.
That is, if E->W wind loads are different than W->E loads, due to for example a monoslope roof, then for the E->W force direction, the E->W force is used for both E->W and W->E directions, then all the deflections are averaged. The same thing is done again for the W->E force direction using W->E loads.
c) Force Distribution
The forces used to calculate the deflection of each segment for the purpose of deflection design are as follows:
i. Force Distribution to Segments within Walls
The unit shear force v used for deflection calculations is the central pier shear force determined through force-transfer shear force distribution to piers (see 5 above). Therefore, the deflections of the segments within the shear wall that are later averaged are not equalized, even if deflection-based shear distribution to segments is selected in the Design Settings.
ii. Force Distribution to Sheathing on Each Side
The distribution of the force to sheathing on either side of a segment in a two-sided shear wall is determined by equalizing the nail slip plus shear components of the deflection equation.
iii. Force Distribution to Shear Wall in a Shear Line
If deflection-based shear distribution to segments is selected in the Design Settings, the force on the force-transfer shear wall in a shearline is determined by equalizing the deflection of the entire wall with other force-transfer or perforated walls, and with all the segmented wall segments on the line. In other words, the segment-averaging process for a force-transfer wall is incorporated into the iterations that equalize shear wall deflections on the entire line.
d) Shear, Bending and Nail Slip Components
The calculation of the shear, bending and nail slip components in the equations for deflection from SDPWS C4.3.2 use the reduced segment height h. The shear and nail slip terms are linear in h; the bending term is proportional to h3.
e) Hold-down Displacement Component
The hold-down displacement contribution to deflection at each interior segment of the force-transfer wall is calculated as if there was a hold-down device at each opening, even though they are not present in force-transfer walls. The wall anchorage term in the equations for deflection in SDPWS C4.3.2 is calculated as follows:
i. Shear Overturning Force
The shear overturning force is calculated using the reduced moment arm of those segments that are considered to extend from the bottom of the opening to the top of the wall. For full-height end segments, the wall height is used as the moment arm.
ii. Dead and Wind Uplift Force
Dead loads and wind uplift loads on the same level as the segment are distributed to the segment ends for the purpose of deflection calculations. Dead and wind uplift loads over openings are distributed to the fictitious hold-downs at the sides of the openings, as if it was a segmented wall.
iii. Forces from Upper Levels
Dead, wind uplift and overturning hold-down forces from floors above are included in the calculation of hold-down deflection if the hold-down forces on the wall above and on the wall below are at the same location. ; that is, these segments behave as segmented walls do in this regard.
iv. Height-to-Width Factor
The factor h/b in the wall anchorage term uses the reduced segment height h for those segments considered to extend from the bottom of the opening to the top of the wall. For full-height end segments, the wall height is used.
v. Hold-down Devices Used
For deflection calculations, the virtual hold-down devices used for the left end of all openings are those selected for the left end of the wall, and those used at the right end of openings are those used at the right end of the wall.
When calculating deflections in the opposite direction, the hold-downs are flipped, so that for one actual force direction, the same hold-down devices are subjected to tension in all the deflections that are averaged to give the resulting wall deflection.
f) Gypsum Materials
The contribution of gypsum wallboard and plaster materials is ignored in calculating deflections of force-transfer walls, regardless of what is set in the Ignore contribution of.. Design setting.
9. Drag Strut Forces
Collectors are required throughout the full length of the force-transfer wall according to SDPWS 126.96.36.199(4). We received confirmation that this clause refers to the transfer of forces from the diaphragm to the shear wall, not the internal transfer of forces around openings via blocking and straps. A continuous collector is necessary because the shear force distribution to force-transfer piers creates differential forces in the top piers of the wall, so that axial tension and compression forces build up in the top plate of the wall, which acts as a collector dragging or pushing the uniform shear force from the diaphragm above to the piers below.
Shearwalls reports these drag strut forces at the sides of each opening and at the ends of the wall where there is a gap in the shear line. These locations are where the local maxima and minima of tension and compression forces occur, and these forces vary linearly between these points.
a) Comparison with Segmented Walls
These are the same locations drag strut forces appear for segmented walls, but the mechanics for force transfer are quite different.
For a segmented wall, there is no shear resistance in the sheathing above openings, so that the drag strut above the first segment with an opening drags additional force into the segment to the left, and pushes additional force into the segment at the right, typically creating tension in the drag strut at the left side and compression at the right.
For a force-transfer wall, the shear force in the sheathing above the opening is typically greater than the corner pier forces, so that the drag strut pushes additional force into the pier above the first opening from the left, and pulls it into this pier from the right. This typically creates compression in the drag strut at the left side and tension at the right.
10. Elevation View
The following changes have been made to Elevation View output for force-transfer walls:
The boundaries of force transfer piers are shown as light blue lines.
b) Pier Forces
Shear forces in each pier are shown at the bottom of each pier in the same way that the design shear force is shown at the bottom of the wall for segmented walls. For offset openings and the non-continuous strap setting, the pier force is shown at the bottom of the pier (lowest opening) for consistency, although the full shear force is developed at the bottom of the higher opening.
c) Segment Shear Forces
The program shows only one large arrow at the top of the wall for the total force on the wall, not forces on each segment as it does for segmented walls.
d) Straps and Strap/Blocking Forces
Straps are shown as two thick, closely spaced lines above and below the openings and extending into neighbouring segments. For continuous straps they extend the full length of the wall at the height of the highest opening top and lowest opening bottom. For non continuous straps, the extend the length of the full height segment adjacent to the opening.
The strap/blocking forces are shown at each corner of the opening. The program does not indicate the direction of the force or whether it is in tension or compression; typically for left-to-right shearline forces, the top left strap is tension, top right blocking in compression, bottom left blocking in compression, and bottom right strap in tension.
A legend entry indicates these are strap/blocking forces.
e) Aspect Ratios
Aspect ratios and factors are shown for central piers only, in the center of the pier.
f) Dimension Lines
The vertical dimensions of piers are shown as follows:
Piers above and below openings are dimensioned in the same horizontal location as the opening dimension line.
Central piers are dimensioned if they are a different height than adjacent openings.
Corner piers are not dimensioned as they have the same dimension as an adjacent opening pier.
For continuous strap across the entire wall, only one set of piers is dimensioned; as piers in all segments have the same dimensions.
The program does not shade the areas above and below openings as it does for perforated and segmented walls, as these areas contribute to shear resistance for force-transfer walls.
h) Show Menu and Display Options
Items have been added to the Show menu and Options | Display settings to allow you to turn on and off the display of piers, straps and pier dimensions.
The following changes have been made to the Design Results output to accommodate force-transfer walls. These changes apply only to force-transfer walls with openings; walls designated as force-transfer without openings are treated as segmented walls.
a) Shearline, Wall and Opening Dimensions Table
In the Shearline, Wall and Opening Dimensions table:
i. Wall Type
A type FT has been added for force transfer walls.
ii. Aspect Ratio
The aspect ratio for force-transfer walls is the aspect ratio of the central pier; this is explained in the Legend.
b) Shear Results Table
i. Shear force v Column
The force v in the column headed by v is the force in the central pier.
ii. vmax/vft Column
The column headed by vmax is now vmax/vft and shows the shear force above and below openings and in corner piers. A legend item explains this, and that the aspect ratio factor does not apply to these forces
iii. Opening Row
A line for openings now appears between each segment giving the unit shear force, total shear force, and design ratio of the piers above and below openings (which always have the same unit shear force).
iv. Aspect Ratio
The legend entry for aspect ratio factor now refers to force transfer piers
c) Deflection Table
i. Line for Entire Wall
For other types of walls, this table shows lines for wall segments only. For force-transfer walls, a line for the entire wall has been added to show the averaged deflection of all the segments in both directions.
The shear force shown in this line is the total force on wall divided by wall length. The wall dimensions and wall group are also shown, but all other columns are not used and show a hyphen (-).
ii. v Column
The column for segment shear force v shows the force in the central pier.
iii. End Segment Deflections
For end segments, the wall height h and the shear, bending, nail slip, and hold-down components of the deflection equation are the average of those derived from the full wall height and the distance from the bottom of the lowest adjacent opening to the top of wall. This is because the end segments are full height in one direction but not in the other.
The averaging of the bending term, which is non-linear in h, has been determined mathematically and does not correspond to the calculation of that term using the h shown.
iv. Interior Segment Deflections
For interior segments, the wall height is the distance from the bottom of the lowest adjacent opening to the top of wall, and all deflection components are determined using that height.
The legend has been modified to explain the wall width b, wall height h, shear force v, hold-down devices used, and total deflection for the entire wall and for each segment, referring to APA T555.
d) Hold-down Displacement Table
i. End Segment Height
The value used for the wall height h to determine total displacement shown for end segments is the average of the full wall height and the distance from the opening bottom to the top of the wall. This is explained in the Legend.
ii. Hold-down Device
The hold-down device shown is the one used to calculate the displacement at the segment, even though a hold-down device does not exist at that location.
e) Collector Forces Table
The Drag Strut Forces table has been renamed Collector Forces, and two columns have been added to show the force-transfer strap/blocking forces at the sides of each opening (the same locations that drag strut forces are currently shown), in each force direction.
A legend item has been added for strap/blocking forces.
- whether the Equivalent Lateral Force (ELF) procedure used by Shearwalls is allowable for each Seismic Design Category, as per 188.8.131.52
- the new regularity criterion for limiting the value of the design seismic response parameter SDS (see).
- the conditions in 184.108.40.206 whereby the redundancy factor ρ is equal to 1.0
- the application of the 25% increase in drag strut forces as per 220.127.116.11.
In the Site Information dialog:
a) Irregularity Groups
Checkboxes have been added for both the N-S and E-W force directions for the following single irregularities or groups of irregularities, which are checked if any one of them is deemed to exist:
i. Horizontal Irregularities
1b Extreme Torsional
2 Corner, 3 Diaphragm or 4 Offset
These correspond to the ASCE irregularities as follows:
- Corner = Reentrant Corner
- Diaphragm = Diaphragm Discontinuity,
- Offset = Out-of-Plane Offset.
If 1a Torsional is checked, then 1b Extreme Torsional is unchecked and vice-versa.
ii. Vertical Irregularities
1a Soft story, 2 Weight or 3 Geometric
1b Extreme Soft or 5a Weak Story
4 In-plane Discontinuity
5b Extreme Weak Story
These correspond to the ASCE irregularities as follows:
- Soft story = Stiffness – Soft Story
- Weight = Weight (mass)
- Geometric = Vertical Geometric
- Extreme Soft = Stiffness – Extreme Soft Story
- Weak Story = Discontinuity in Lateral Strength – Weak Story
- In-plane Discontinuity = In-plane Discontinuity in Vertical Lateral Force Resisting Element
- Extreme Weak Story = Discontinuity in Lateral Strength – Extreme Weak Story
b) Files from Older Versions
Previously the choices were
Horizontal irregularity or in-plane vertical irregularity
Other vertical irregularity.
When opening project files from previous versions, if the first of these was checked, then 2 Corner, 3 Diaphragm or 4 Offset is checked for both directions. If the second was checked then 1a Soft story, 2 Weight or 3 Geometric is checked for both directions.
The irregularities and directions selected are listed in the Site Information section of the Seismic Load Generation Details
d) Use Detected Torsional Irregularity for Design
A checkbox has been added called Use detected torsional irregularity for design. This means that if the program detects a torsional irregularity during the analysis of the structure for design, but one was not selected in the Site Dialog, it applies that irregularity to the determination of whether ELF is allowable, redundancy factor ρ, and the 25% drag strut force increase. Conversely, if no torsional irregularity is detected but one was selected in the Site Dialog, the torsional irregularity is not applied.
For Seismic Design Categories D, E or F with vertical irregularity 5b, and SDC E or F with horizontal irregularity 1b or vertical irregularities 1b or 5a, the program warns you that the Equivalent Lateral Procedure (ELF) is not permitted by ASCE 7 18.104.22.168. If only the horizontal Torsional irregularity 1b exists, this applies only if rigid diaphragm design is selected.
The warnings appear if vertical irregularities 1b, 5a, or 5b are selected in the Site Information dialog, or if the following conditions are satisfied
- Rigid diaphragm design is selected in the Structure Input view, and
- Use detected torsional irregularity is not selected and Torsional Irregularity 1b is selected, or
- Use detected torsional irregularity is selected and Torsional Irregularity 1b is detected by the program.
a) Site Information Dialog
If a combination of inputs leading to Seismic Design Category, and Irregularity inputs, in the Site Information dialog correspond to prohibited ELF, a message appears saying seismic design is prohibited by 22.214.171.124.
b) Screen Messages
When Load generation is invoked, if ELF is prohibited, warning messages appear on the screen informing you of the reason. Note that at this point, the Torsional irregularity has not been checked by the design routine, so only the input irregularities in the Site Information dialog are used.
When shear wall design is invoked, similar warning messages appear, this time informed by the possible detection of the extreme Torsional irregularity.
c) Design Results Output
If ELF is prohibited, notes appear below the Seismic Information table and the appropriate Shear Results tables informing you of the reason and saying the results are for information only and should not be used to design the structure. A message appears in the Design Summary referring you to the Seismic Information table. The notes under the Shear results tables are displayed in red.
3. Redundancy Factor, ρ
a) ASCE 7 Requirements
For Seismic Design Categories D, E and F, structures with an extreme torsional irregularity (horizontal 1b), must have a ρ = 1.3 (in the case of E and F, the program will also warn that the Equivalent Lateral Force procedure is not allowed, see2 above). Otherwise, for these categories, satisfying one of two conditions allow ρ to be 1.0 rather than 1.3:
Condition a – Involves removing elements and checking for story strength and existence of extreme torsional irregularity 1b with the elements removed.
Condition b – The structure is regular in plan (no horizontal irregularities), and a check is made for sufficient perimeter framing.
b) Existing Implementation
Version 11 of Shearwalls detected the extreme torsional irregularity 1b to automatically assign ρ = 1.3 to structures in SDC D, E, and F, and to perform the checks for condition a with the elements removed. For condition b, it incorrectly used the Other vertical irregularity input to check for regularity of the structure.
c) New Implementation
i. Extreme Torsional Irregularity
For rigid diaphragm design, the program assigns ρ = 1.3 for SDC D-F if
- Use detected torsional irregularity is not selected in the Site Information dialog and Torsional Irregularity 1b is selected, or
- Use detected torsional irregularity is selected and Torsional Irregularity 1b is detected by the program.
ii. Condition a
The program detects the possible extreme torsional irregularity when elements are removed; the input in the Site Information dialog is not used to determine this irregularity.
iii. Condition b
The plan irregularity check is made by checking for torsional irregularities 1a or 1b in the same manner described in Extreme Torsional Irregularity (i above). The structure is also deemed irregular if any other horizontal irregularity is checked in the Site information dialog.
4. 25% Drag Strut Increase
a) ASCE 7 Requirements
According to 126.96.36.199, for Seismic Design Categories D-F, the collector (drag strut) forces based on the diaphragm design force Fpx from 188.8.131.52, is increased by 25% if the structure has any horizontal irregularity relevant to Shearwalls, or if it has vertical regularity 4, In Plane Discontinuity.
b) Existing Implementation
In Version 11, the increase was applied for SDC D-F to all drag struts in the building if you selected Horizontal Irregularity or In-Plane vertical irregularity in the Site information dialog
c) New Implementation
For Seismic Design Categories D-F
i. Torsional Irregularity
For rigid diaphragm design, the 25% increase is applied if
- To all drag struts in the building if Use detected torsional irregularity is not selected in the Site Information dialog and Torsional Irregularity 1a or 1b is selected, or
- Use detected torsional irregularity is selected and Torsional Irregularity 1a or 1b is detected by the program on the level with the drag strut.
ii. Input Irregularities
The 25% increase is applied to all drag struts in the building if any of the other horizontal irregularities (than torsional irregularities) are selected in the Site Information dialog, or if Vertical Irregularity 4 – In plane discontinuity is selected.
iii. Horizontal Irregularity 4 – Out-of-Plane Offset
The 25% increase is applied if on the level above the drag strut, anywhere on the level above the shearline with the drag strut, there is a shearline in that direction with no line on the level below. This is regardless if this irregularity is checked in the Site Information dialog.
In the Collector Forces table (formerly Drag strut forces), a line has been added to the legend to explain the conditions under which the 25% increase is applied.
5. Limit on Value of SDS
Refer to A.4.d)iii above, under Maximum SDS Value in the Determination of Cs and Ev (184.108.40.206), for the application of the new regularity criterion to this provision.
A note has been removed from the Hold-down Design table regarding Irregularities not being checked.
Refer also to the changes listed in the section with the same name under Version 11.2,
The method of determining external pressure coefficients CpCg for low-rise structures from ASCE 7 Figure 28.3-1 assumes symmetric, rectangular structures. They are based on boundary layer wind tunnel studies of buildings of that shape, verified against full scale measurements. As relatively few low-rise structures have such a regular shape, Shearwalls now extends this method to buildings with multiple blocks and/or eccentric ridge lines.
a) Intersecting Blocks
When two blocks intersect such that the slope of a portion of a roof can be formed either by either the side panel of one block or the end panel of the other, such as one roof framing into another to form an L-shape, the manner in which the building is modelled does not affect the wind loads generated when the load generation option of treating end hip panels as side panels is chosen. However, if the ASCE 7 C28.3-2 is used, then it does make a difference. It is recommended to use the side panel option with wind load generation. If the C28.3-2 method is used, it is best to join blocks such that composite roof surfaces formed by the hip end of one block and the side panel of another are avoided.
The area of exterior walls beneath a sloped roof are considered to “have” the slope of the roof for the purpose of Case A (transverse) load generation, which depends on roof angle. If there is a hip end in the Case B (longitudinal) direction, and side panel Case A coefficients are used on the wall beneath the hip end, they are the same as the rest of the building face formed by the side panel of the other block.
A hip end panel in the same plane as a side panel on another block has the co-efficient from the same load case as the side panel, so it is equivalent to the situation where the side panel from one block forms the roof on the entire face and the other block joins that block without forming a hip end.
b) Differing End Panels
Previously the program disallowed structures for which the hip ends on opposing ends of a block had different slopes, or there was a hip on one end and a gable on the other. Now these structures are allowed, and the coefficients used on the roof panels and the walls below the panels are based on the angle of each roof panel.
c) Eccentric Ridge Lines
Previously the program disallowed the case of an eccentric ridge line with different slopes on either side of the ridge. Now this case is allowed, and the coefficients used on the side roof panels and the walls below the panels are based on the angle of each roof panel. This applies to each roof on a structure with multiple blocks.
d) End zones
End zones are created wherever the corner of a block is an exterior corner of the structure. End zones are not created where two blocks join each other forming either a straight wall and roof, or an interior corner.
e) Basis for Height-to-Width Limit Design Setting
The data group Apply height to-width ratio to…has been changed to Low-rise height-to-width limit based on… and provides choices for Single block and Entire structure. The definition of low-rise structures in ASCE 7 26.2 says they must have mean roof height less than least-horizontal dimension, and in the absence of guidance in the ASCE 7, this setting is used to specify whether this limit is to be applied to each block or to the structure as a whole.
Note that the Apply height to-width ratio to… setting had no effect in previous versions of the program, as they did not allow multi-block low-rise structures.
f) Screen Warnings
The error messages that appeared after Generate Loads was invoked saying that load generation was not possible due to unequal hips, eccentric ridge lines, or multiple blocks, have been modified to provide warnings and suggestions for these reasons, but to indicate load generation will proceed.
g) Load Generation Details
In the Load Generation Details output:
i. Header Note
A note in the header section of the Wind Load Generation Details output indicates that the building does not conform to strictly to Figure 28.3-1 for the following reasons, which are only included if applicable to the structure: multiple blocks, eccentric ridge lines, or unequal hip or gable ends.
ii. Load Table
There are now load tables for each block for multiple block structures, where previously only one table was possible.
h) Torsional Analysis Details
If there are multiple blocks of which any two have orthogonal ridge lines, then both Case A and Case B loads can exist in the same wind direction on different blocks. In this case, in the Torsional Analysis Details output where it otherwise says Low-rise Case A or Low-rise Case B, it says Low-rise Case: and then Wind Generally North-South or Wind Generally East-West.
For orthogonal ridge lines, where the section for Case A previously had results for only one load direction, there are now results for both directions.
i) Show Menu Options
Since Case A and Case B loads can exist in the same wind direction on different blocks, for multi-block structures, in the Show menu and associated Options settings under Display,
- Wind Load Case is changed to Wind Direction
- the Case A Side, Case B End show menu option is disabled
- the words (Case A) and (Case B) are removed from the North-South and East-West options
Previously, Shearwalls analyzed low-rise wind loads from ASCE 7 Figure 28.3-1 by considering pressures in the E-W and N-S directions independently and did not consider the combined effect of these pressures on torsional analysis for rigid diaphragm force distribution to shearlines.
Shearwalls now includes loads due to pressures from both directions in the torsional analysis routine simultaneously, so that torsional forces from E-W loads are considered when determining N-S forces, and vice-versa.
Note that it is only Case B that has simultaneous pressures in both directions.
a) Load Cases Considered
This has been implemented for the Basic Load Case only and will capture torsional effects due to structural asymmetry and end zone effects. The Torsional Load Cases in Figure 28.3-1 which specify partial loading have not been implemented in Shearwalls.
In the torsional analysis routine, the program now calculates the torsion T in the equation
Fti = T Ki li / (Jx + Jy)
as Tx + Ty for both directions, when previously Tx was used for one direction and Ty for the other. Refer to the Torsional Analysis Details output for the definitions of these variables.
c) Torsional Analysis Details Output
In the Torsional Analysis Details file (previously the Log file) , for load Case B
- A note has been added to the top saying explaining the simultaneous design, referring to Note 3 in Figure 28.3-1.
- The Concentrated Load F, Center of load Cl and Eccentricity etx values are shown in a table at the top for both directions, rather than separately for each direction. F and Cl now show subscripts for direction, e.g. Fx and Cly
- The equation of torsions has been modified to show both directions rather than one.
The following improvements were made to the equalizing of deflections of the sheathing on either side of a shear wall, as a step in the process of equalizing deflections along the shearline as required by SDPWS 220.127.116.11.1. This affects force distribution to segments within a shearline when using the deflection-based distribution Design setting. Equalizing deflections on both sides of the wall for the 4-term equation C4.3.2-1 entails equalizing the sum of shear and nail slip terms in the equation, as the bending and hold-down terms affect both sides equally. For the linear 3-term equation from SDPWS 4.3-1, only the shear term is equalized.
a) Numerical Procedure for 4-term Equation (Change 45b)
For the non-linear 4-term the program now implements the Newton-Raphson numerical procedure rather than a more time consuming “brute force” procedure. The Newton-Raphson method always converges to a solution when there is one, in less than 10 iterations as opposed to 100 or more for the brute force method and converges more reliably.
The Newton-Raphson method is used to solve the non-linear equation
δi(vi) = δe(ve),
where δ is the sum of deflections from the linear shear term and non-linear nail slip term. Subscripts i and e refer to the interior and exterior sides of the segment.
This can be reformulated as a one-dimensional problem as follows,
D(ve) = δe(ve)- δi(v-ve) = 0,
where v is the known force on the segment.
The Newton method follows the slope (derivative) of D(ve) down to the ve axis.
The derivative is
dD/d(ve) = d(δe(ve)-δi(v-ve))/ dve.
It is convenient to calculate the derivatives with respect to both vi and ve , and noting vi = v - ve
dD/d(ve) = dD/d(vi) = dδe(ve)/d(ve) + dδ(vi)/d(vi),
dδ(ve)/d(ve) = h/gvtv + 0.75hβ(s/12γ)β veβ-1, and similarly for vi,
where s is nail spacing in inches and γ and β are parameters from SDPWS Table C4.2.2D.
b) Algebraic Procedure for 3-term Equation (Change 45c)
When using the Design setting that linearizes the non-linear 4-term equation into a linear 3-term equation, the program was unnecessarily using the same slow iterative approach as was used for the non-linear 4-term equation. It now solves this equation algebraically. Defining α = h / 1000 Ga as the shear term factor of v in the linear 3-term equation and α i and α e represent α value on the interior and exterior,
ve = v αi / (αi + αe)
vi = v - ve
c) Assignment of No Force to One Side of Wall (Change 45a)
Occasionally, all forces were placed on one side of the wall when there should have been some force on both sides. This was a problem with the “brute force” iterative procedure and has been corrected in the course of implementing numerical methods.
In the Torsional Analysis Details file, distances such as center of load, center of mass, shearline location and eccentricity have been based on a fixed co-ordinate system with its origin in the southwest corner of the structure. S->N distances are positive, and N->S are negative.
The forces F, however, are based on the direction of applied force; for N->S applied force, all values in the N->S direction are positive; for S->N applied force, they are negative.
Some users find this confusing and wish to see all values relative to the same fixed co-ordinate system. Other users, however, wish to see positive shearline forces when they are in the direction of the applied force, and this corresponds to the way they are presented in the Plan view drawing.
Accordingly, we now offer a choice in the Options settings of showing forces based on a fixed co-ordinate system, or relative to the applied force.
The program now displays the loads to be used for diaphragm design derived from Fpx defined in ASCE 7 Equations 12.10-1,2, and 3, and the shearline forces derived from these loads that are used for drag strut design as per 18.104.22.168.
Note that as per 22.214.171.124, diaphragm design forces are minimum forces, and if the effects of the loads derived from structural analysis in Section 12.8 are greater, these should be applied.
a) Control of Display
Items have been added to the Show Menu under Loads saying Diaphragm Design Loads and under Forces saying For Drag Strut Design, which are enabled when viewing the Seismic load case in the Loads and Forces view only, i.e. not when in Generate Loads view.
b) Diaphragm Design Loads
The loads shown are those derived from Fpx, including transfer forces from the floor above, distributed in proportion to the building masses on that level, i.e. they have the same load profile as the loads for shear wall design derived from Vx from Eqn. 12.8-13, but a different magnitude.
i. Transfer Forces
Transfer forces from discontinuous shearlines on the level are shown in Shearwalls as point loads on the level below. When diaphragm loads are shown, this load is factored by the overstrength factor Ω0.
as per 126.96.36.199.
ii. Critical Loads
These loads are always shown when Diaphragm Design Loads is selected, even though they may not be the critical ones for design of every diaphragm element. In some cases, the Fpx-based loads are of a lesser magnitude than the Vx-based loads, but the increased transfer force from a discontinuous shearline makes these loads critical for some part of the diaphragm. For this reason, it is left to the judgment of the designer as to which set of loads to use to design an element.
c) Shearline Forces
The shearline forces shown are those used for drag strut design, that is, the largest of the forces derived from Fpx-based loads and Vx -based loads.
For Seismic Design Category A and B, only the Vx-based forces are shown, as ASCE 188.8.131.52 applies only to Categories C-F.
d) Seismic Load Generation Details
For the following items, definitions of have been added to the Legend to the Seismic Load Generation Details and equations added to the Equations section.
- Diaphragm design force Fpx,
- Fpx-based building mass element force Fpe
- Fpx -based shearline force Vpjx,
- Discontinuous shearline force Vdjx
- Collector shearline force on shearline force Vcjx
Forces from discontinuous shearlines from the floor above are shown in Plan View on the level below as a point load. However, there is also a point load in the same place from the building mass from the lower half of the wall on the level above. These two forces obscured each other. Now, the transfer force from the level above has been repositioned such that both forces are visible.
7. Redundancy Condition b for Seismic Design Category D to F
Regarding the condition “b” of ASCE 7 184.108.40.206 under which structures in Seismic Design Category are permitted to have a redundancy factor ρ = 1.0:
a) Number of Bays
In determining whether the determined whether the required seismic force resisting “bays” existed, the program was not restricting the calculation to those stories that had more than 35% of the seismic base shear. Note that according to ASCE 7 220.127.116.11, virtually all stories of 5-6 story structures have 35% of the base shear, so this problem was unlikely to arise.
b) Force Directions
A literal reading of ASCE 7 12.3.4 would suggest that the factor ρ = 1.3 be applied in both directions if conditions (N-S and E-W), a and b were not satisfied in just one of them, and that is the way Shearwalls was operating. However, we applied were not being calculated separately in each direction (N-S and E-W), and if it was not satisfied in either it would result in ρ = 1.3 in both; now it is evaluated for each direction separately.
a) Wind Load Cases
When seismic loads are selected, the Wind Load Case options are now disabled. Previously the selections were available but had no effect.
b) Force / SFRS Direction
The Force Direction item has been renamed SFRS Direction, for consistency with the change to MWFRS for wind. SFRS stands for Seismic Force Resistance System
c) Load / Force Direction
The Load Direction input has been renamed Force Direction, as the shearline and hold-down forces are the only things that could potentially change when an opposing direction is selected.
9. Output of Shear Factor Cvx for Seismic Design Category A (Bug 3200)
For Seismic Design Category A, in the Distribution of Base Shear table of the Seismic Load Details file, nonsensical values were shown for the vertical distribution factor Cvx from ASCE 7 Eqn. 12.8 -12. This is because Cvx is not applicable to SDC A as per ASCE 7 11.7 and 1.4.
The column for the Cvx factor now shows a “-“ in this case, as does the hx * wx column, which is not relevant to SDC A either.
Refer also to the changes listed under Version 11.2,
The program user interface has been changed to have a more up-to-date look and feel. Consequently:
a) Asterisk and Note for Editable Drop-down Boxes
Editable drop-down boxes now have a different appearance than for those you can only select a value, so the asterisks appearing before these boxes and the corresponding notes at the bottom of Beam and Column View have been removed.
b) File Save and File Open Boxes
For Sizer 11, the program reverted to an old-fashioned style of standard Windows File Open and File Save as dialog boxes that had not been in use since Sizer 9.x. The more modern boxes that were used in Sizer 10 have been restored.
A new menu item Open Autosaved File menu has been added under File menu to provide direct access to auto-saved backup files BackupPre.wsw and BackupPost.wsw. Refer to the On-line Help for the use of these files. Explanatory status bar messages are displayed if you hover over the menu items.
3. Menu Item for Change History
An item Features and Changes has been added to the Help menu, which accesses this Change History document.
The following changes have been made to the display of drag strut forces in Elevation View
a) Location of Symbol and Force
The symbol with a circle and arrow showing the drag strut force has been moved up to be just below the top of the wall. Previously the forces were shown at the top of openings. The drag strut forces are typically in the top plate of the wall, not the opening headers, and this change avoids conflict with the new force-transfer strap forces.
b) Direction of Arrow
The direction of the force arrow now indicates whether the drag strut is in tension or compression at that point. Previously the arrows always pointed away from the opening or wall end.
An arrow in the direction of the shearline force is in tension, one contrary to the shearline force is in compression. An arrow in the same direction as the shearline force pointing into an opening segment is dragging the force over the opening into the full height segment. An arrow in the opposite direction pointing into an opening segment shows the full height segment resisting force
being pushed into it from over the opening.
The following change has been made to the output of drag strut forces in the Collector Forces table of the Design Results (formerly Drag Strut Forces)
c) Negative Compression forces.
The magnitude of the drag strut a force in compression is shown with a negative sign. The legend explains that positive numbers are in tension, negative ones in compression.
5. Default Standard Walls
The following changes have been made to the Standard Walls that are included by default in Shearwalls
a) Wall Framing Species (Change 31)
The wall stud species for all six standard walls has been changed to S-P-F from D.Fir-L, as spruce-pine-fir is more commonly used than Douglas Fir-Larch. .
b) Nail Size (Change 31a)
The nail size for the three exterior standard walls has been changed to unknown from 8d. Because these walls have unknown sheathing thickness, a known nail size limits the sheathing sizes that can be selected, which is not desirable for a default wall.
Now, the default size for new openings is 3 feet with an offset of 2.5 feet from bottom of the wall, approximating the size for a window. Previously the default size for a new opening was 6.75 ft approximating the size for a door.
In Plan View legend for the CAD Import action shows segmented walls as diagonal rather than solid, as they appear that way in this view in order to reveal the CAD drawing. The legend item Aspect factor is no longer shown in this action as it is not relevant
The following changes have been made to the Display items in the Options Settings, and/or the corresponding items in the Show menu, which control program elements to display or output.
a) Elevation View (Change 57)
For the Show menu that appears while Elevation View and/or the Elevation View column in the Options Settings,
i. Center of Loads and Center of Rigidity
Checkboxes for Center of loads and Center of rigidity have been added under Elevation view in the Options Settings. Previously, they had only been in the Show menu
ii. Aspect Ratio
Aspect ratio has been moved to appear below Segment numbers.
iii. Nailing Information and Legend
The Nailing information used to mistakenly hide and show the legend. It has now been renamed Legend. Nailing information now is shown and hidden via the Sheathing information item.
iv. Shear Force and Capacity
An item has been added to show or hide the design shear force and combined capacity information, which previously were always shown. This allows the entire material specification \to be removed if all Show menu items are turned off.
b) Spelling of Story (Change 20c)
For the Show menu that appears while viewing Design Results and/or the Design Results column in the Options settings, the word Story was misspelled as Storey for both wind and seismic story drift. This has been corrected.
The following changes have made to the Design Settings input
a) Reference to Wind Serviceability Provision (Change 85)
The ASCE reference in the Wind serviceability data group title has been changed from ASCE 7 CC.1.2 to ASCE 7 CC.2.2. CC.1.2 was the reference in ASCE 7-10. Also, the word limit is now capitalized.
b) Location of Shearline Materials Checkbox (Change 85)
The checkbox titled All shearwalls on shearline have identical materials and construction was moved into the Design procedures group box.
c) Brackets in Moisture Percentage (Change 85)
Brackets have been added to the text appearing underneath the Fabrication and In-service inputs in the Service conditions group box. The text e.g. <=19% and >19% is now changed to (<=19%) or (>19%).
d) Unnecessary Word “Calculation” (Change 85)
The word calculation has been removed Perforated shearwall Co factor calculation.
e) Hyphenation of Gypsum-based (Change 27)
A hyphen has been included in gypsum-based in the Design Setting for excluding walls sheathed entirely with these materials, and in warning messages that appear when wet service conditions are set for disallowed materials.
The following changes have been made to the Shear Results Table of the Design Results
a) vmax Definition (Change 65)
For perforated walls, the definition of vmax in Legend to the Shear Results table has been changed to collector and in-plane anchorage force from collector shear force, because this force also applies to the to anchorages from the wall to the floor for both shear force ( SDPWS 18.104.22.168.1.1) and uplift (22.214.171.124.2.1). Shearwalls does not, however, specify these anchorages.
b) FHS Explanation
The explanation of FHS as “full height sheathing” as been moved from the definition of vmax to that of v, where it first appears.
c) Criterion Spelling
The misspelling of the word criterion as criterior has been corrected.
11. Seismic Zone Restrictions in Seismic Information Table
The terminology Seismic Zone has been changed to Seismic Design Category in the small section under the Seismic Information table listing restrictions based on Seismic Design Category.
Consistent capitalization of Kzt and Kz, rearrange a bit.
Important: Shearwalls 2019 and Version 11.2 were released simultaneously, so please consider both this list and the changes listed under Shearwalls 2019 as the record of changes for Shearwalls 2019. Changes listed under Shearwalls 2019 are not in Version 11.2.
In Design Settings, when the setting for all shear walls on shearline having identical materials was not set to be true, the program was not detecting the violation of condition a of ASCE 126.96.36.199, which is one of two conditions that must be untrue if the redundancy factor is set to 1.3 rather than 1.0. Therefore, dissimilar shear walls, a redundancy factor was never applied to seismic shearline forces when the redundancy input was set to Calculated (rather than 1.0 or 1.3) in the Site Information. This has been corrected.
Note that Calculate redundancy and not to force identical materials are the default settings.
For walls with same materials on both sides of the wall and unknown sheathing thickness, the program assigned zero force to the wall while designing, so that any wall would pass design and there was zero wall deflection. The zero force appears in the deflection results, the shear design results, and no design shear shown at the bottom of the wall in the Elevation view drawing.
Wall parameters related to hold-downs were being included in the definition of standard walls, although they are not part of the material specification intended to be part of a Standard wall: As a result, the following would occur if these were changed for a wall:
- If Design in Group was not selected, the wall would no longer be designated as being one the Standard walls. Extra design groups would be created for all the walls affected.
- If Design in Group was selected, the change would be propagated to all other walls that were part of the Standard wall group.
a) Hold-down Data
The following data were not available for selection in Standard Wall mode, but were being treated as Standard Wall parameters:
- hold-down model,
- number of brackets,
- whether to apply the same hold-down to the openings.
b) No. of End Studs (Bug 3307)
The number of end studs, which is used only for hold-down design, has been removed from the standard wall definition for the purpose of design grouping but is retained in the Standard Wall mode of Wall Input View for the purpose of creating default walls.
Hold-down related information is no longer included in the Standard Wall definition because hold-downs are designed separately from walls, and it is desirable to group walls according to wall materials only.
The importance factor used for the maximum and minimum diaphragm design force from ASCE 188.8.131.52 (Eqn.'s 12.10-2 and 12.10-3), and for the out-of-plane of wall Forces using 12.11.10, was always 1.0 rather than the importance factor corresponding to the Risk Category selected in the site dialog.
The incorrect diaphragm design forces were used for drag strut design and appear in the Seismic Information table. The incorrect out-of-plane forces appear in Elevation View.
The program was not applying the unblocked factor Cub from SDPWS Table 184.108.40.206 to the nail slippage term in the non-linear 4-term equation C4.3.2.-1. SDPWS 220.127.116.11 says to divide v in the 3-term equation 4.3-1 by Cub, but there is no direct guidance on whether or how to apply it to the 4-term C4.3.2.-1. The program applied the factor to the shear and bending terms in the 4-term equation, but as the nail slip en term includes v only indirectly, it was not applied to nail slip.
Since Commentary equations C 18.104.22.168.-1 and -2 indicate that it should be considered a stiffness -reducing factor, we decided to divide the deflection due to non-linear nail slip by Cub, rather than apply it to the v before it is raised to a power in the determination of en.
The convergence routine for equalizing deflections along the shear wall as required by SDPWS 22.214.171.124.1 sometimes left a small residual on a segment that should not attract any force, causing the program to report that it could not equalize deflections. The program now zeroes out the force if it is less than 0.05 plf, that is, what appears as 0.00 in the output. Note that it adds this small force back into the pot to be redistributed to other shearlines, so it isn’t leaking forces if several segments are zeroed out.
7. Shear Stiffness Gvtv for Unknown Sheathing Thickness (Bug 3269)
When determining the shear-through-thickness Gvtv from SDPWS Table C4.2.2A used in the shear term of the 4-term deflection equation in C4.3.2-1, and indirectly via determination of Ga in the 3-term equation 4.3-1, when the sheathing thickness had been left unknown, the program was using the Gvtv for the thickest sheathing option, or 23/32”, rather than the thickness for the sheathing being designed. This caused a non-conservative error in the shear term of the 4-term deflection equation of about 5%. The shear term is usually a small component of the overall deflection.
We have changed the way the program incorporates forces from shearlines on upper levels in the rigid diaphragm analysis on the level below.
a) Previous Procedure
In versions before Shearwalls 11.2:
i. Seismic and Non-Torsional Wind
For seismic design, and the non-torsional wind cases (ASCE Envelope Procedure form Figure 28.3-1 and ASCE Directional Procedure, Case 1 from Figure 27.3-8) Shearwalls included the unfactored shearline forces derived from flexible diaphragm analysis on the level immediately above and added them to the applied loads on the level for which rigid analysis was being performed. The shearline force was then factored by the 0.6 load combination factor.
i. Torsional Wind
For ASCE Directional Case 2 loads, Shearwalls included the applied loads from all levels above and added them to the applied loads on the level for which rigid analysis was being performed. The shearline force was then factored by 0.6 for wind design
b) New Procedure
For both wind and seismic design, the shearline forces arising from rigid diaphragm analysis from the level immediately above are applied to the rigid diaphragm analysis on the floor below. For each shearline, the worst case of forces from positive and negative accidental eccentricity on the level above are those which are transferred.
c) Background and History
i. Rationale for Previous Procedure
When the rigid diaphragm procedure was implemented along with multi-story analysis in version 2002 of the program, there was concern that the torsional effect of the accidental eccentricities applied on the level above should not be carried through to the level below for two reasons:
1. Probability of Simultaneous Occurrence
It was thought that accidental eccentricity is entirely to account for inaccuracies in the distribution of mass in a structure, and that it was unlikely that these inaccuracies or variabilities would occur on each level and in the same direction.
2. Compounding of Accidental Eccentricity
There was a concern that the eccentricity would unnecessarily compound, that is, the effect of eccentricity on the level above creates amplified forces that would be further amplified by the eccentricity on the level below.
We received guidance at that time that it would be acceptable to apply loads derived from flexible forces on the floor above to rigid analysis on the level below.
ii. Use of Applied Loads for Non-torsional Wind Design
The Case 2 Directional torsional wind requirement was determined to apply to flexible diaphragms and added to the program for version 10, in 2013. In order to avoid compounding this eccentricity, applied loads on the levels above were used in lieu of shearline forces. This was an internal change only, there is no effect on the resulting torsional moments.
d) Reason for Change
i. Probability of Simultaneous Occurrence
ASCE 7 C126.96.36.199 says that it is “typically conservative to assume that the center of mass offsets of all floors and roof occur simultaneously and in the same direction.” That is, as we cannot know for certain which levels and directions the accidental eccentricities occur in, it is best practice to assume they occur on all levels.
ii. Effect of Compounding vs Flexible Diaphragm Inaccuracy
Typically, accidental eccentricity adds approximately 10% force to the shearline experiencing the greatest effect. Compounding this effect on the floor below by adding 10% of 10% = 1% is not a significant increase and is much less than the inaccuracy that arises from using the flexible diaphragm forces from the shearlines above. Flexible diaphragm analysis can result in a markedly different distribution of force than the rigid diaphragm force, and by using flexible forces, the program was not transferring the inherent torsion from the floor above to the one below.
e) Consequences of New Procedure
i. Distribution of Non-torsional Direct Forces
The new procedure uses the direct forces due to shear wall stiffness on the level above, rather than those arising from flexible analysis. As we are assuming rigid diaphragms on all levels, this is a significant improvement in the accuracy of the procedure.
ii. Distribution of Inherent Torsional Forces
The new procedure transmits inherent torsional forces due to physical offset between the center of mass and center of rigidity, and these forces contribute to torsion on the level below. This is the correct procedure, as an object when subject to torque twists throughout its whole length. The old procedure did not transmit torsion between levels.
iii. Distribution of Accidental Torsional Forces
On each line, the program transmits the maximum force from positive and negative accidental eccentricity. As such, the new procedure will transmit the increase in force due to accidental torsion but will not transmit the torsional effect of that force, as the worst case of the positive and negative accidental torsions on opposite extremities of the structure tend to cancel.
We believe this is an acceptable compromise between the conservative procedure described in ASCE 7 C188.8.131.52, and the non-conservative procedure of not including accidental eccentricities from the floor above on the floor below at all.
For All heights wind load generation procedure, when a wind shearline force was added directly to a shearline using the Add as a factored force directly… input in the Add Load input form, for rigid diaphragm analysis the force had an effect on only the level it was added on and was not being transferred below for inclusion in the torsional analysis on the level below.
This has been corrected in the course of implementing the changes in Bug 2733, above, Vertical Distribution of Rigid Diaphragm Shearline Forces.
In the case of buildings with flat roofs and on the upper level of the structure, the generation and distribution of low-rise wind loads using ASCE Fig 28.3-1 were incorrect in several ways. In such buildings, the longest direction of the building is considered to be the direction parallel to the ridge line for buildings with roofs. The following problems were identified and corrected
- Case A (transverse to long direction) loads were being generated on end walls, however such walls are not loaded in the ASCE model
- Some Case A loads were being created with the magnitude intended for Case B loads, and vice versa
- For torsional analysis of load Case B (wind force parallel to long direction), no force was being included parallel to the long direction
For generation of wind loads, when a block with roof overhangs was adjoined to another block, the program would create loads on the roof the block was adjoined to in the portion shadowed by the block, even if the Exclude roof portion covered by other block checkbox in the Load Generation input was checked. This happened when using the load generation procedures for both low buildings and all other buildings.
The following problems pertaining to wall out-of-plane seismic force Fp from ASCE 7 12.11.1, which is shown in Elevation view, have been corrected.
a) Wall Weight in Calculation (Change 78)
The program was using only the weight W of ½ the wall height in the calculation Fp= max( 0.4 SDS Ie* W, 0.1W) when it should have been using the full wall height.
b) Display for Rigid Diaphragm Analysis (Change 79)
Fp is now shown for both rigid and flexible diaphragm analysis. Earlier, it was shown only for flexible analysis.
It is now possible to select multiple walls on which to apply loads in the Add Load dialog. Once walls are selected using the Control Key or Select All command, upon entering the Add Load dialog,
- Point loads cannot be selected,
- Apply to is disabled and shows Selected Walls,
- The From and To locations are blank and disabled,
- The Add as a factored force directly to the shearline is not available
Loads are then added on all selected walls, with the Magnitude From and To being the load magnitude at the start and end of each wall.
For multiple blocks, the program occasionally failed to update the roofs according to the input in the data group Construction in Roof Input View in the following ways:
a) Disabled Joined Selection
If there is another block that a roof could join to, the Joined selection was sometimes disabled so the operation was impossible.
b) Gable and Hip Selections
When roofs are joined in the N-S direction, the Gable and Hip selections sometimes had no effect and the roof remained joined when selected.
These have been corrected.
When the wall height is changed in Structure input, the program now adjusts the top of any openings to ensure that they remain within the confines of the wall and removes the openings that would have no height if this is done.
In Elevation view, non-full height segments, that is, those that do not meet aspect ratio limits in ASCE 7 Table 4.2.4, were not shown in grey out as they are for segmented walls. They are now greyed out, because such segments do not contribute to shear resistance and are not included in the summations of segment lengths used for Co factor calculations (184.108.40.206), hold-down forces (220.127.116.11.3), and in-plane shear anchorage (18.104.22.168.1.1).
When the end of an opening on an upper storey is over the interior of an opening on the floor below, the drawing in Elevation view of the vertical element extending from the bottom of the upper floor joist to the top of the opening was no longer visible because it was obscured by the gray shading over non-full-height sheathing segments that was introduced with version 11.
This has been corrected.
Dimensions for walls, wall segments and openings were being rounded to the closest 1/16th of an inch in Elevation view when the Decimal format for Imperial output was chosen in the Format Settings, e.g. a length of 12.08 feet was rounded to 12.063 feet. The true dimension as input is now shown.
For a one-story structure, the Levels indicator is shown in the Extend to field. Now it is shown in the Current level and the Extend to field is invisible in this case.
The following changes have been made pertaining the symbols that appear in Plan View in the Load Generation and Loads and Forces actions showing the Center of Load and Center of Rigidity for Torsional Analysis
a) Show Menu Item Activation
The show menu items for center of load and center of rigidity were always disabled in Loads and Forces view, only becoming active in Load Generation view. This has been corrected and they are active in both views.
b) Center of Loads for No-load Cases
When there are no loads in a direction, such as for low-rise wind load Case A, the program showed the Center of Load in the direction without loads at the zero location, making it difficult to notice. In this case, it has now been moved to where the Center of Rigidity is located.
c) Overlapping Symbols
When the center of loads and center of rigidity are in the same place or close to it, the symbols CL and CR now longer overlap.
When a wall is selected in Plan view and turns orange, the other walls on the shearline turn a darker colour of orange (or brown). Previously they were purple.
The word Direction indicating the ASCE 7 load generation method in the Plan View legend has been changed to Directional in accordance with ASCE 7 Chapter 27 nomenclature.
For narrow Elevation view windows, and when the hold-down and/or drag strut Design Setting is set to Shearwall capacity, the Legend heading Factored Forces overlapped with perforated wall aspect ratio information shown under the walls.
When in Plan view and you close the input form, e.g. Opening Input, either by the exit button on the form window or by the Input Form icon in the toolbar, then go to another Plan view action, e.g. Roof Input, and return, the input form for the original action now re-appears. Previously it remained invisible and some users had difficulty making it reappear.
The program now displays three separate reports for detailed wind and seismic load generation and torsional analysis calculations, rather than all three in one report as before, and outputs three files with this information rather than one.
a) Toolbar buttons
The toolbar button that previously showed the word log and is called Load Generation and Torsional Analysis Details has been replaced by three buttons, one which shows three single-ended arrows and is called Wind Load Generation Details, another showing three double-ended arrows and is called Seismic Load Generation Details, another which shows a semi-circular arrow and is called Torsional Analysis Details.
The button for the primary design results has been changed to convey the tabular nature of that output.
b) Menu Items
The File menu item Log File has been removed, and the following files are now accessed from menu items in the View menu.
Wind Load Generation Details
Seismic Load Generation Details
Torsional Analysis Details
The word View has been removed from Design Results View, for consistency with these menu items.
c) File Output
The file with extension .log file has been replaced by three files with extensions .sws, .sww, and .tor.
Previously, the combined file was output when loads were generated, then appended to after Design button was pressed when the torsional analysis is performed. If loads were then regenerated, the torsional analysis results were lost. Other synchronization problems occasionally occurred.
Now, the Load Generation Details files are output when loads are generated and Torsional Analysis Details when the design is performed, eliminating any interference between the two.
The titles and headers to the load generation and torsional analysis results have been redesigned to achieve a consistent format across all three intermediate output files, torsional analysis, wind load generation, and seismic load generation. In the subheadings giving the load generation procedures, Wind Load Generation and Seismic Load Generation have been set to all capitals to make them stand out.
f) Getting Started Steps
The 14th and final step in the introductory Getting Started window has been modified to refer the Torsional Analysis Details, Wind Load Generation Details, and Detailed Shearwall Design output reports rather than the log file.
Starting with version 11.1, a crash occurred if the exterior sheathing material of the wall was changed after loads were generated. Sometimes it happened immediately, other times after other program operations were performed. This has been corrected.
If a project is run such that torsional analysis is required, then the inputs are changed such that it is not and run again, the program retained the Torsional Analysis Details from the previous run. If torsional analysis is not required because the Rigid analysis option is not selected and there are only seismic loads on the structure, the torsional analysis report no longer appears.
The following link has been added to the Help menu for a user to navigate to a video tutorial from within the program. (http://cwc.ca/woodworks-software/support-and-training/tutorials/
If the hold-down database was empty or corrupted, a crash occurred on program start-up. The program now re-installs the original database if it encounters a corrupt or empty one. It was possible to avoid the crash by deleting the corrupted hold-down database file.
Occasionally, when a shearline in a structure had a no full-height-sheathing segments, the program would crash upon entry to Elevation view.
After running design, thee Design Results are now shown in the last selected view style, Wide View or Preview. Previously it returned to Preview each time. The program still defaults to Preview on the first design run.
The instructional steps that appear when the program is run or “Getting started” is invoked from the toolbar have been revised, clarified and updated. Some of the more significant changes are:
a) Default Values
A “Step 0” has been added suggesting setting defaults for building elements, and the subsequent steps indicate how those defaults are used to create the structure.
b) Edit Walls
Explanations of the ability to change the location and size of walls via the wall input form, the selection of Standard Walls, designing for unknowns, and designing as a group have been added.
c) Edit Hold-downs
A Step 7 has been created for editing hold-down device information, by moving instructions from other steps.
d) Generate Loads
An instruction to set the Wind Load Generation Procedure has been added, and the procedure of creating seismic loads in stages with self-weights on each level explained more clearly.
e) Add or Edit Loads
The need to add dead loads to counteract overturning, and wind uplift loads, has been emphasized. An explanation of changing building masses and returning to regenerate loads has been added, as has the case of not generating loads and adding loads to check a single shearline. The unusual case of modifying generated loads has been removed.
Several design settings have been added to the recommendation to set the Rigidity and Deflection options before designing. The mention of design processing time has been removed, as it is no longer a major issue.
g) Accept or Adjust Design
A Step 15 has been added for the Accept Design feature.
h) Detailed Results Output
The step formerly called “Log File Output” has changed to View Detailed Results, and lists the separate buttons and associated files for wind load generation, seismic load generation, and torsional analysis, that used to be in one file
The following changes have been made to the Display items in the Options Settings, and/or the corresponding items in the Show menu, which control program elements to display or output.
a) Design Results
For the Show menu that appears while viewing Design Results and/or the Design Results column in the Options settings.
i. Hold-down Design and Collector Force Tables (Bug 3228)
The inclusion of the Hold-down Design table and Collector Forces (formerly Drag Strut Forces) table in the Design Results output is now controlled by separate items in the Show menu and in the Options settings. Previously they were both controlled by a single item in the Loads and Forces settings.
ii. Wind Story Drift and Deflection (Change 20b)
b) Wind Direction in Loads and Forces Settings (Bug 3240)
In the Loads and Forces settings, the check boxes labelled Southwest, Northeast, Southeast, Northwest have been changed to show Wind from Southwest, etc.
c) Drag Strut Spelling (Change 57f)
In the Show menu, under Forces, Dragstruts has been changed to Drag Struts.
The following changes were made to the text in messages:
a) Warning Message for Rounded Opening Input Values (Change 48)
The warning message about opening input being rounded to the nearest snap increment, identified the input by long phrase that did not make sense in the context of the warning. It has now been abbreviated to briefly identify the input, e.g. Offset from edge.
Square brackets around the input value have also been removed.
b) Loads and Forces Warning Message Misalignment (Change 4)
The warning message when Loads and Forces view for the first time had misaligned bullet points. This has been corrected.
c) Hip Roof Wind Load Generation Message (Bug 3294)
A message that appeared on wind load generation explaining that the program uses side panel coefficients on the hip ends has been removed, as it appeared out of context. Previously it appeared as part of a warning that the building does not conform to the ASCE 7 model, but that part was removed, leaving an unnecessary message.
d) R and Cd Warning Message for Gypsum (Change 66)
In the warning message that appears when a greater value
of Response modification factor R and Deflection amplification factor Cd are
input in the Load Generation Site Information for a direction having
non-wood-panel shear walls, mistakenly structural wood panels is output instead
of non-wood panels and this has been corrected.
12. Change of Spelling in User Interface (Change 111) *
All references in the user
interface to “shearwalls” and “shearlines” have
changed to “shear walls” and “shear lines”, as this is the correct spelling and
the one used by CSA O86.
The following changes have been made to the Wall and Shearline Input form and/or the Openings Input form:
a) Shearline Selection in Wall Input View (Change 24)
The Shearline input is now disabled if there is no choice other than Auto. This input allows you to select the shearline a wall belongs to if the walls are within the allowable shearline offset of walls defining two or more shearlines. As the default offset in the Design Settings is only 6”, this rarely occurs, and the use of this input was unclear to some users.
b) Relative Rigidity for Standard Walls (Change 63)
The input for relative rigidity appearing in Wall Input view when in Standard Wall mode has been removed. You can no longer enter this value when modifying a regular wall, and now serves only to show the rigidity of the designed wall relative to others. It has no meaning for Standard Walls.
c) Irrelevant Warning Message for 1-ply Gypsum Wallboard (Change 93)
A warning message about nail length limitations from an irrelevant design code appeared when the mouse was clicked anywhere in the input form, when Gypsum Wboard 1-ply was selected the sheathing material and Drywall screws, fastener type, with the fastener Size in focus, This has been corrected
d) Hold-down Information
The following changes have been made to the inputs of hold-down information.
i. Hold-down Selections for Perforated Walls (Bug 3267)
For perforated walls and for the new force-transfer walls, the Apply hold-downs to openings checkbox in Wall Input form, and all input in the Hold-down data group in the Openings Input form, are now disabled because hold-downs are not placed at wall openings for these types of walls.
ii. Hold-down Dropdown Box Style (Change 82)
The hold-down model input has been changed from an editable drop-list to a noneditable list, as a hold-down typed into this input would not necessarily match with an existing one in the database.
The following changes have made to the Design Settings
a) Disabled Worst-Case Rigid vs Flexible Diaphragm Setting (Change 54)
The check box for Worst-Case rigid vs flexible diaphragms was disabled and showing as selected if only one of Rigid or Flexible Analysis was selected in the Structure input. Now it is shown as not selected (empty) in this case.
b) Reset Original Moisture Conditions (Change 46)
The Moisture conditions did not reset to their original values, 15% for Fabrication and 10% for In-service, when Reset original settings was pressed. This has bene corrected.
c) Hold-down and Drag Strut Data Group (Change 84)
The date group Collector forces based on in the Design Settings has been renamed Forces based on , as the definition of Collector in ASCE 11.2 includes drag strut as a synonym, so that hold-downs cannot be considered a “collector” This change has also been reflected in the Design Settings output.
The redundant word “forces” has been removed from the column headers in the data group which now say Hold-downs and Drag struts.
d) SDPWS References in (Bug 3312)
In the SDPWS Deflection Equation data group, the SDPWS reference for the 3-term equation option was 4.2-1, the equation for diaphragms, and has been changed to 4.2-1, the one for shear walls.
The reference for the 4-term equation was listed as C4.3.2-2 , the Commentary reference for 3-term, and has been changed to C4.3.2-1, the correct equation for 4 term.
The references have also been corrected in the Design Settings output table. The correct equations were used in design; this was only a display issue.
e) Apply height to-width ratio to… Setting (Change 85a)
The data group Apply height to-width ratio to…has been removed from the Design settings, as it applies only to multi-block low-rise structures, which are not permitted in version 11.2.
Note that Shearwalls 2019 incorporates these structures and includes the setting Low-rise height-to-width limit based on….
f) Default Ignore Gypsum Setting (Change 106)
The option to ignore the contribution of gypsum-based materials for narrow wall segments is now checked by default, as it is normally advantageous to do this.
Other settings changes:
g) Hold-down Settings Input Field Sizes (Change 244)
Sime of the inputs in Wood Properties and Construction Details section of the Hold-down settings were too small to show typical data without scrolling and have been enlarged.
h) Save as Default for New Files (Change 255)
The following settings were not being saved as defaults when Save as default for new files was selected.
- Line 4 of company information under Company Information
- Worst-case rigid vs. flexible diaphragms in Design Settings
This has been corrected.
i) Reset Original Settings (Change 257)
i. Moisture Conditions
Fabrication and In-Service Moisture in Design Settings were not being reset to their original value after you reset original settings.
ii. Snap Increments
The Snap Increments input in Plan View and Elevation View settings was not being re-enabled if the Display gridlines was not checked before you reset original settings. It is now enabled after the reset because Display gridlines is checked in that case.
The following changes have been made to the Site Information input form
a) Default Fa and Fv For Site Class F (Change 26)
If Site Class F is selected in the Site Information and the Fa and Fv values now show zeroes rather than the values from the last site class selected; and if you exit the dialog without the program now issues a warning message asking you to enter non-zero values. If OK is selected, you return to the input dialog; If Cancel is selected, the changes are reverted.
b) Link to Wind Speed Map (Change 42)
The link to the wind speed map in the Site Information has been updated to refer to the new web address https://hazards.atcouncil.org/ for the Applied Technology Council’s Hazards by Location website. The previous site expired on June 30, 2018. Note that as of March 21, 2018, it is a beta release of the website
c) Link to Seismic Data Map (Change 91)
The reference to the seismic maps containing site coefficients S1 and SS in the has been changed from https://earthquake.usgs.gov/designmaps/ to https://seismicmaps.org/ . The new link is from the SEAOC/OSHPD Seismic Design Maps Tool that is referenced in the web site from the old link, the U.S. Geologic Survey (USGS) Earthquake Hazards site, however it is amongst many other links on that site and it was not clear which one to choose.
a) Update of Values (Change 8)
In Generate Loads dialog, the following values reverted to their original values after being edited and you clicked anywhere outside the box before generating loads:
- all self-weight text fields
- Horizontal projection check box
- Use wall self-weights…for Jhd calculations check box (Canada only)
- line/area load radio buttons
- C&C wall loads check box
The program now retains all the inputs.
b) Update of Low-rise Hip Roof Method Selection (Bug 3294)
The choice of using low-rise side panel coefficients or using ASCE -7 Fig. C28.3-2 was sometimes disabled even when there were hip roof panels on the structure. This has been corrected.
a) Openings in Floor Area Note (Change 7e)
A note to enter a mass with negative magnitude to represent an opening in the floor now appears at the bottom of the Add a New Load box when Building mass and Area load are selected, to make users aware of this possibility.
b) Add Load to Selected Wall (Change 254)
If no wall was selected and Selected wall was chosen in the Apply to... combo box when adding a new load, a large value automatically appeared in the From X= and To X= fields. Furthermore, you are allowed to enter a load which appeared on a random building face.
The program has been changed to revert to the previous Apply to... selection in this case.
c) Wind Uplift Loads on Selected Walls (Change 95)
For wind uplift loads, in the Application input of the Add a New Load dialog box, you can now add the loads to selected walls. Previously only the full wall line was available.
The following change has been made to the Design Settings table of the Design Results output.
a) Deflection Analysis not Performed (Change 83)
In the line saying Deflection Equation in the Design Settings output, if Include deflection analysis is unchecked in Design Setting, No deflection analysis is shown rather than Never or Always.
This is because the deflection equation is irrelevant if there is no deflection analysis; also, the Include deflection analysis setting was not previously reported in the output.
The following change has been made to the Sheathing Materials table of the Design Results output.
In the Sheathing Materials table of the Design Results output for OSB materials, the number of plies last selected for plywood was shown. As plies are irrelevant to OSB, a dash now appears.
The following change has been made to the Seismic Information table of the Design Results output.
a) Seismic Design Category Terminology (Change 68)
The section under the table called Seismic Zone Restrictions has been renamed to Seismic Design Category Restrictions in accordance with the terminology in the ASCE 7.
The following changes have been made to the Shear Design table of the Design Results output.
a) vmax Reference in Legend (Change 53)
The legend entry for vmax, the shear force for collector and connection design, now refers to SDPWS Equation 4.3-9 instead of the incorrect reference to 4.3-8.
b) Shear Force in Kips (Bug 3319)
In the Shear Results table, the shear force and allowable shear force were shown in lbs when kips were selected as the imperial force unit setting even though the table header showed kips. This was only a display issue; design was not affected. The values are now shown in kips.
The following changes have been made to the Hold-down Design table of the Design Results output.
a) Hold-down Model Number for Offset Perforated/Segmented Walls (Bug 3327)
In some cases of segmented walls on the lower storey and perforated walls above where the openings did not line up vertically, for one of the openings on the lower level the table did not show the hold-down model number, although design results were shown for the hold-down. This has been corrected.
b) Load Combination Note (Change 105a)
The first two notes under the table regarding ASCE 7 load combinations and seismic forces Eh and Ev have been combined into one note that makes the relation between the signs in the equations and the directions of the forces clearer. The ASCE 7 reference numbers have also been updated.
c) Anchor Bolt Note (Change 105b)
The note below the table giving anchor bolt washer size requirements has been changed to indicate that the design of the connection from wall to floor or foundation is not performed by Shearwalls, and that anchor bolt requirements are from SDPWS 22.214.171.124.3. The previous note sometimes misled users into thinking that the “shear” column in the table was for horizontal shear in the foundation anchors, and not the overturning force in the hold-down.
Furthermore, this note appeared for seismic design only, although the SDPWS requirements apply to both wind and seismic. The new note is output for both.
The following problems with the reporting of the uplift t force for perforated walls from SDPWS 126.96.36.199.2.1 in the Hold-down Design table were corrected. These forces occur when perforated walls and openings in them on upper levels do not line up walls on the levels below.
i. t Force When Combined with Overturning (Bug 3326)
When an overturning force exists at the same location, the program did not report the t component, so that the combined forces did not equal the sum of the components. A new line is now shown below the existing line showing the t component in the Shear column (but not the Combined column), at a position labelled e.g. t @ Op 1.
ii. Isolated t Force (Bug 3326)
When the t force was the only component of the hold-down force, the program previously output a line with the t force in the Combined column only at a position labelled e.g.I Op1. It is now in both the Shear column and Combined column at a position labelled t @ Op 1.
iii. Legend (Change 13)
There was no explanation in the Legend of the t forces that sometimes contributed to the Combined force, or what was meant by I Op1, for isolated t forces. A legend entry for t @ Op n has been added, referring to SDPWS 188.8.131.52.2.1.
e) Reporting of Hold-down Model for Offset Perforated/Segmented Walls (Bug 3327)
When there were segmented walls on the lower storey and perforated above, and openings do not line up vertically, openings on the lower level one of the ends did not have a hold-down model number listed in the Hold-down table when there should have beeen one when at the location of a tensile hold-down force. This has been corrected.
f) Perforated Wall Note (Change 105c)
The reference in the note regarding the perforated wall force should has been changed to SDPWS Eqn. 4.3-8, from SDPWS 4.3-9.
a) SDPWS Table Reference Number (Change 67)
The reference in the legend to SDPWS Table 3.21 for out-of-plane sheathing capacity has been corrected to 3.2.1.
a) Hip Roof Wind Load Generation Method (Bug 3294)
The choice of using side panel coefficients or using ASCE -7 Fig. C28.3-2 for low-rise hip roof generation now appears in the Site Information section.
b) Terrain Exposure Constants (Change 74)
The misspelling of Terrain in Terrain Exposure Constants, and the alignment of the epsilon-bar constant have been corrected.
The following changes have been made to the Seismic Load Generation Details report (formerly part of the Load Generation Details report).
a) R and T in Site Information (Change 59)
In the Site Information section,
i. Repeated Note
Two separate notes indicated that the response modification coefficient R and period T are shown in the base shear table. The first has been removed,
ii. Response Modification Factor Symbol
The symbol for the response modification coefficient factor was mistakenly shown as Rd, Ro. This has been changed to R.
b) Base Shear Tables (Change 60)
i. Total Design Base Shear Table
- The table has been renamed Total Design Base Shear, from Calculation of the total design base shear:
- Added note about manually entered seismic loads and forces not being included.
ii. Distribution of Base Shear to Levels Table
- The table has been renamed Distribution of Base Shear to Levels from Distribution of total design base shear to Levels
- Added note about manually entered seismic loads and forces not being included in the distribution.
- the alignment of column headings Csmax, Csmin, Cs and V have been corrected so they appear above the data shown. (Change 14)
9. Torsional Rigidity Jy Output for Rigid Analysis (Change 80)
The value displayed in the Jy column of the Torsional Rigidity line in of the Torsional Analysis Details report had some extra digits after the number making it much too large. This was only a display issue and the erroneous value was not used in the calculation.
Because the newly added wind story drift limitations from ASCE 7 CC.1.2 can be difficult to meet and are not mandatory according to ASCE 7 Appendix C, a design setting has been added to activate the calculation of wind story drift, and Option setting and Show menu item to allow you to turn off the output of story drift output tables independently for wind and seismic design.
a) Design Setting
A new data group called Wind serviceability ASCE 7 CC.1.2 has been added to the Design Settings page. In it there is a new checkbox allowing you to control whether to calculate story drift for wind loads, and the existing setting to enter the drift limit as a ratio of storey height.
b) Options Setting
The Options setting controlling which design results tables to view that previously said Storey shear table is now two settings Story shear – seismic and Story shear – wind.
c) Show menu
The Show menu now has two items – Story drift – seismic and Story drift - wind instead of just Story drift.
2. Perforated Shearwall Issues
Several problems associated with perforated walls, particularly with the capacity adjustment factor Co from SDPWS 184.108.40.206, were corrected:
a) Co Factors Greater than 1.0 using SDPWS Eq’n 4.3-5 (Bug 3220)
The program calculated Co factors significantly greater than 1.0 while using SDPWS Equation 4.3-5 (as opposed to Table 220.127.116.11), when there are narrow segments in the wall, because the SDPWS does not explicitly limit Co to 1.0. When there are no narrow segments to which an aspect ratio factor is applied, as per the note to the definition of ∑Li in 18.104.22.168, the minimum limit of h/3 the opening height ensures that Co can never be greater than 1.0, but it can be when the aspect ratio factor is applied.
This was particularly evident when there are no openings in the wall and no need for a perforation factor, but one was made anyway on the assumption that it would always be 1.0. The program now limits Co to 1.0, and does so even when there are openings, as we believe this to be the intention of the SDPWS.
b) Design Results Using Co Factor from Wall on Upper Story (Bug 3225)
Occasionally, the Shear Results output table displays the Co factor for a wall on the story immediately above a wall, rather than the correct factor for that wall, and shows a capacity and design ratio based on that factor. This is just a reporting issue, and these values were not used to design the wall or determine deflections and force distribution.
c) Truncated Perforated Shearwall Issues
The following bugs apply to the perforated shearwalls such that one or more openings in the shearwall have no full-height segments between them and one end of the wall, so that the non-full height segments and adjacent openings have been stripped from the wall for calculation of Co.
The problems are particularly evident when there are no openings left in the truncated wall and no need for a perforation factor, so that the Co factor should be 1.0, and the factors were showing up as any number.
The incorrect Co factors appeared in the shear results table and in elevation view, and were used in the calculation of shearwall capacity and hold-down forces.
These problems all been corrected.
i. Co Factor for Truncated Perforated Shearwalls Using Equation 4.3-5 (Bug 3231)
For truncated perforated shearwalls the value of the total opening area Ao in SDPWS equation 4.3-5 still included the length the openings that should have been ignored. The total shearwall length Ltot was calculated correctly by excluding the openings, leading to nonsensical values of Co.
ii. Co Factor for Truncated Perforated Shearwalls Using Table 22.214.171.124 (Bug 3232)
For seismic design of truncated perforated shearwalls, the total shearwall length Ltot in note 2 of Table 126.96.36.199 was sometimes including the length of the segments and openings that should have been ignored, whereas the sum of segment lengths ∑Li excluded them, leading to incorrect Co values. For wind design the correct Ltot was used, leading to inconsistent seismic and wind Co values.
iii. Uplift Force t for Truncated Perforated Shearwalls (Bug 3234)
Truncated perforated shearwalls were showing the anchorage uplift force t from SDPWS 188.8.131.52.2.1 on non-full-height segments that had been ignored in the calculation of Co.
This uplift force t appears in elevation view and is not used for other calculations and has no effect on shearwall design or force distribution. It has now been removed from these segments.
This occurred when an opening was than extends to the very end of a wall, meeting a perpendicular wall. If the location of the wall with the opening is then moved, followed by moving the wall it meets, the gap is created.
This problem has been corrected.
When a wall was underneath a gable end from a monoslope roof, the hold-down forces calculated were nonsensically large. This has been corrected.
Occasionally, when project files were opened in Structure view, they did not allow the activation of the input form button and did not show the Structure Input form. Upon moving to any other view, the program would crash.
This problem could be avoided by pressing the Structure input button, after which the program operated as it normally does. The program no longer crashes when this happens, but it is still necessary to click the Structure button to view the Input form.
The following bugs pertain to the disabling and re-enabling of the Design Setting Ignore contribution of … Gypsum-based materials … combined with wood structural panels … based on the state of the Allow 3.5:1 aspect ratio setting,
a) Dependence on Ignore for Seismic Design Setting
The disabling/enabling happened only when the Ignore contribution of … All gypsum materials …seismic design setting was unchecked. This was the behaviour of the corresponding settings for the previous version, but with the SDPWS 2015 implementation, these settings should now be independent. This setting is now enabled whenever Allow 3.5:1 aspect ratio is checked.
b) Greying of Text
When the checkbox is disabled, the program now still shows the text explaining the setting, instead of greying it out.
The word “table” has been removed from several Options Settings in the Display design results group, as it had been inconsistently applied to some design results tables and not others. The setting that previously said Materials table now says Sheathing/framing materials; in all other cases the word “table” has just been excised.
The data group title Ignore non-wood-panel contribution… has changed to Ignore contribution of…. so that the elision of the title and the checkbox text, which had been changed for the 2015 SDPWS implementation, now makes grammatical sense.
This version released to address the following problems:
When the setting "Rigidity for shear force distribution based on… is set to use the deflection of wall segments and the 3-term equation is selected for the SDPWS deflection equation setting, and there are non-full-height sheathing segments present, sometimes the forces were distributed in an inconsistent and unpredictable manner from one design to the next. This affected the distribution of forces along the shearline, the distribution of forces to the shearlines for the rigid distribution, and ultimately shearwall design. This issue was due to random problems with memory allocation in the computer, and has been resolved.
For projects made with previous versions to version 11, if the Disregard shearwalls height to width limitations had been set, the Plan View and Elevation View elements relating to aspect ratio did not appear, and upon design the program issued a Windows error message and froze.
This setting was removed for v11, but if you Reset Original Settings, the program stabilized so that the user interface elements would appear and you could run a design. In any event, the problem has been fixed and no longer occurs in version 11.0.1.
The major features implemented for this version are
Numerous other improvements have been made to all areas of the program. The following is an index to descriptions of the changes listed below.
Version 11 of Shearwalls updates several design codes and standards used in the program. The details of the associated changes to the program appear throughout the rest of this list of changes; this section just identifies the design standards changed.
The implementation in Shearwalls of the IBC has been updated from the 2012 edition to 2015, the NDS from 2005 to 2012, and the SDPWS from 2008 to 2015
a) ICC International Building Code (IBC 2015)
Version 11 of Shearwalls implements the 2015 IBC, whereas Version 10 implemented the 2012 version.
IBC 2015 references the AWC Special Design Provisions for Wind and Seismic (SDPWS 2015) for all design provisions*, whereas IBC 2012 referenced SDPWS 2008. Extensive changes for the 2015 SDPWS edition were implemented, as described in b) below.
IBC 2015 continues to reference ASCE 7-10 for all wind and seismic load generation procedures. Since both Shearwalls 10 and Shearwalls 11 implement ASCE 7-10, no changes were needed for these provisions.
*except those using staples, which are not permitted by SDPWS. Shearwalls does not include staples, so all procedures in the program comply with IBC by complying with SDPWS.
The SDPWS had been updated from the 2008 version to the 2015 version for Shearwalls 11. The most consequential changes are listed here and described in more detail in later sections of this document.
i. Force Distribution Method and Aspect Ratio Factors
Deflection-based distribution is established as the preferred method of allocating forces to segments within a shearline. Capacity-based distribution is restricted to wood or fiberboard shearwalls, and a more stringent aspect ratio factor is applied to the strength of narrow shearwall segments when it is used.
ii. Perforated Wall Aspect Ratio Adjustment
Previously, the strength of a perforated wall was factored by the aspect ratio factor for the narrowest segment in the wall. Now, the length of wall used to determine the Co factor is adjusted instead, leading in general to much lower penalties for narrow segments.
iii. Same Materials and Construction on Shearline
The design code clarified what is meant by the restriction to similar materials and construction on a shearline, so that shearwalls with differing sheathing thickness and nailing patterns are now allowed on the same line, as long as they belong to the same class of materials (wood structural panels, gypsum wallboard, fiberboard, etc.)
iv. Same Materials and Construction on Opposite Sides of Wall
Although it is not explicitly mentioned in the SDPWS, in communications with WoodWorks AWC confirmed a that the same redefinition of similar vs. dissimilar materials should be used when combining sheathing capacities from materials on opposite sides of the wall.
v. Fiberboard Deflection for Narrow Segments
A new provision requires that the deflection fiberboard segments with an aspect ratio greater than 1:1 be increased by the square root of the aspect ratio.
vi. Out-of-plane Sheathing Capacity
The out-of-plane sheathing capacity for resistance to C&C wind loads has changed for some materials.
c) ANSI/AWC National Design Specification for Wood Construction (NDS 2015)
Version 11 of Shearwalls conforms to the NDS 2015, whereas version 10 conformed to NDS 2012. There are very few procedures in the Shearwalls program taken directly from the NDS, as all shearwall and diaphragm provisions are now in the SDPWS, to which the NDS refers. None of the provisions taken directly from the NDS have changed for this edition.
The references to design standards have been updated in the following places:
a) Welcome, About Shearwalls, and Building Codes Dialog
The new design standards implemented are listed in the Welcome dialog box that appears on program start-up, and can be invoked later via the Help menu, and in the About Shearwalls box from the Help menu. More detailed information is given in the Building Codes dialog box invoked from the Welcome box.
In the Building Codes dialog, the reference to the NDS clause that references the SDPWS has changed from Chapter 14 to 184.108.40.206.
b) Log file
The log file, which gives the equations used for wind and seismic load generation and for torsional analysis, has been updated for the new design code references.
The header to the log file now says that it implements IBC 2015 and SDPWS 2012, as well as the existing ASCE 7-10 references.
c) On-line Help
The On-line Help documentation has been updated to refer to the current design code editions.
Where necessary, references to design code clause numbers in program messages, notes, table legends, etc., have been updated, as follows.
In general, clauses were added to the SDPWS but the existing provisions kept their original numbering. There were no instances of changes to SDPWS clause numbers in the program.
References to clauses from Chapter 10 of the NDS were incremented to Chapter 11, and Chapter 11 to Chapter 12. References in Shearwalls to 10.3.6 for fastener slippage were changed to 11.3.6, and nail withdrawal capacity 11.2-3 was changed to 12.2-3.
c) On-line Help
The few design code clause references that have changed have not yet been updated as within the On-line Help as of the date of the software release. The Help is now accessed over the Web, and will have the updated references by Feb 2017.
The WoodWorks package no longer installs a .pdf files for the On-line NDS and On-line SDPWS on your computer. The Help menu links and Start menu icons now direct you to websites where viewable versions of the NDS, the NDS Supplement, and the SDPWS are accessed.
Note that the NDS Commentary is no longer included.
In the Building Codes dialog box that is accessed from the Welcome box:
A note has bee added saying that nail withdrawal and hold-down bolt elongation procedures are taken directly from the NDS design standard.
The reference to the removal of the 1997 UBC design code has itself been removed
This section deals with the engineering provisions and calculations only; how they are reflected in program operation, drawings, and output reports is described in later sections.
In what follows, the symbol b is the segment length between openings/wall ends and h is the wall height as shown in the wall input view, that is, not including the height of the floor joist.
As per SDPWS 2015 220.127.116.11.1, the Aspect Ratio factors and adjustments (currently called H/W factors in Shearwalls) now depend on the choice of shearwall rigidity method in the Design Settings.
As before, these factors are applied over a range of aspect ratios of 2:1 to 3.5:1 for wood structural panels (WSP) and 1:1 to 3.5:1 for fiberboard. However, the WSP factors are now applied to both wind and seismic design, whereas formerly only the fiberboard factors applied to both.
a) Capacity-based rigidity
When Shearwall capacity (wood panels and fiberboard only) is chosen, the program applies an aspect ratio “adjustment” of 2b/h for WSP and 0.1 + 0.9 b/h for fiberboard, for both wind and seismic design.
Note that these are the aspect ratio factors for seismic design from SDPWS 2008. The changes for 2015 for capacity-based design involve a change in the fiberboard adjustment for wind design to what was previously the seismic factor, and the application of the WSP adjustment to wind design when the factor was previously only for seismic.
b) Deflection-based rigidity
When Deflection of wall segments or perforated walls is chosen, the program applies an aspect ratio factor of 1.25 - 0.125 h//b for WSP and 1.09 - 0.09 h/b for fiberboard, for both wind and seismic design
The factor for WSP is new and now applies to both wind and seismic, not just seismic as before. The factor for fiberboard is the previous factor for wind design, now applied to both wind and seismic.
c) Perforated Walls
The aspect ratio factor from SDPWS 18.104.22.168 is no longer be applied to perforated walls, as per SDPWS 22.214.171.124. This factor for perforated walls is now always 1.0. The new “adjustments” for capacity-based force distribution from 126.96.36.199.1 are not applied either.
Instead, the length of the wall used to calculate the perforated wall factor Co is shortened for narrow segments as described in the following section. This results in a greatly reduced penalty for narrow segments for perforated walls.
In determining the sum of segment lengths ∑Li as defined in SDPWS 188.8.131.52 the program now multiplies any segment lengths Li with aspect ratios between 2 and 3.5 by 2b/h, as per SDPWS 184.108.40.206. This applies to walls of any sheathing material type.
The calculation of ∑Li is modified in this manner for the following purposes:
a) Perforated Wall Factor Co
The calculation of Co using SDPWS Table 220.127.116.11 and using Equations 4.3-5 and 4.3-6, which are newly implemented in Shearwalls.
b) Hold-down Forces T and C
The calculation of Perforated Wall tension and compression hold-down forces T and C using SDPWS Eq’n. 4.3-8 in 18.104.22.168.2.
c) In Plane Anchorage Shear Force vmax
The calculation of the in-lane force transmitted to collectors, vmax using SDPWS Eqn. 4.3-9. In 22.214.171.124.1.1. vmax is shown in the Shear Results table.
d) Anchorage Uplift Force t
The anchorage uplift force t based in vmax in SDPWS 126.96.36.199.2.1. This force appears in Elevation View.
e) Deflection of Perforated Walls.
The deflection of perforated walls using SDPWS 188.8.131.52, both in the use of vmax and in the calculation of segment length b, which is taken as ∑Li.
The SDPWS Commentary C184.108.40.206 clarifies what is meant by “same materials and construction” along a shearline to mean that classes of materials such as wood structural panels, gypsum wallboard, fiberboard must be the same, but details such as the sheathing thickness and nailing patterns do not have to be identical.
Shearwalls previously imposed a stringent interpretation of this rule, applying all the inputs in the Wall Input form to every wall on a shearline. The program now allows dissimilar materials to the extent of the new Commentary, and as further clarified in discussions with AWC.
This new interpretation necessitated changes in the input of walls and in the output of results that are described elsewhere; this section pertains to engineering design implications.
a) Design Setting
A Design Setting has been added to allow you to continue to use the old method that forced identical material specifications on a shearline, or to allow the same type of material but different details.
Shearwalls are considered as having the same material and construction if they are all sheathed with the same materials from the following broad classes
- Gypsum-based (GWB, Gypsum sheathing, Plaster and lath)
- Wood structural panels (Structural sheathing, Structural 1, Plywood siding)
- Lumber sheathing
c) Combination of Sheathing Materials
According to AWC, the intent of this clarification is that all walls on a line must be composed of the same composition of material classes, e.g. wood on one side and gypsum on the other, except that it is possible to have no material on one of the sides and still be considered the same composition.
The case of alternating sides, e.g. wood/gypsum on one wall and gypsum/ wood on another wall, is not allowed in Shearwalls even though it is permissible in the AWC interpretation of the SDPWS. It has been restricted in Shearwalls for simplicity and due to the rarity of its occurrence in real structures.
d) Separate Wall Design
Previously, the program ran the design routine that determines the choices for unknown materials just once for each shearline. Now, if you choose to allow different material details for each wall in a line, the program runs the design separately for each wall. Note that this can result in increased processing time and impractical designs with slightly different details on adjacent walls. This can be mitigated by defining Wall Groups which force the same wall design.
e) Iterative Design for Capacity-based Distribution
Previously, only deflection-based design used iterative design based on the distribution of forces within a line, that is, redesigning shearwalls after forces are redistributed to shearwall segments based on the previous design. For capacity-based distribution with identical materials on each wall, shear distribution per unit foot to the segments did not change based on new designs.
Now that different material details are allowed on each wall in a line, the force distribution can change, and the program now performs iterative wall design to stabilize the distribution of shearline forces on the wall. The program runs down the line and designs the walls, then distributes forces and designs again. The process is repeated until succeeding iterations result in the same wall designs on each wall, or until 5 iterations are made.
Note that the deflection-based routine does only 2 iterations. The capacity-based distribution method iterates more times because
- It doesn’t have the processing overhead of the deflection procedure, which must first iterate numerous times to equalize deflections
- Distribution based directly on wall capacity is likely to be more sensitive to wall design changes than that based on stiffness, which is only partially due to wall materials, but affected more by geometry and hold-down elongation.
The clarification in the SDPWS Commentary C220.127.116.11 regarding what is meant by “same materials and construction” along a shearline inspired a re-evaluation of the definition of similar vs. dissimilar materials on opposite sides of the wall. The following changes were made after consultation with AWC as to the intent of the SDPWS 18.104.22.168 and its subsections.
a) Combination of Identical Materials
The program will continue to add the sheathing capacities of opposite sides of the wall as per 22.214.171.124 only if walls are identical in every material respect, In the case of wind design, they are also added when using the Exception for combinations of structural panels or fiberboard and gypsum given in 126.96.36.199.2.
For materials of the material same class (i.e. wood structural panels, gypsum-based, fiberboard, etc.; see 3.b) above), but where any material property such as nail spacing or sheathing thickness is different, the sheathing combination rule given in SDPWS 188.8.131.52.1 is used. It involves apportioning the shear strength in relation to the relative apparent stiffnesses Ga of either side of the wall.
This method had not been employed previously in Shearwalls because the program used only the 4-term deflection equation, which does not include Ga, and because prior to the clarification in the SDPWS and by AWC as to the definition of dissimilar materials and construction, it was unclear how this method applied to our Shearwalls model.
i. Blocking Factor
Although the SDPWS indicates that nominal (that is, unfactored) shear capacities are to be used, for sheathing nailed to blocking on both sides of the wall, including the blocking factor in the calculation of both Ga and vs is equivalent to applying the blocking factor after the sheathing combination is done.
For sheathing nailed to blocking on just one side, there seems no other way to incorporate the blocking other than to use Ga1, vs1, etc. factored by the blocking factor. So, the blocking factor is applied to all Ga’s and vs’s when performing this calculation. Note that it is rare to nail sheathing to blocking on only one side.
ii. Aspect Ratio Factor
Shearwalls applies sheathing combination rules to materials after the aspect ratio factor has been applied, whereas the SDPWS procedure uses unfactored vs. Since both sides have the same material type thus the same aspect ratio factor, applying the aspect ratio to vs1 and vs2 is equivalent to applying it to the resulting vs, and the Shearwalls methodology is equivalent to the SDPWS procedure.
iii. Wind Design
Although 184.108.40.206.1 specifies that this procedure is for seismic forces only, it is also done in Shearwalls or wind, as per recommendations from AWC.
Via a new Design Setting, the program now allows you to choose between the formulae in SDPWS 4.3-5 and 4.3-6, and Table 220.127.116.11 in determining the Co factor that is applied to the capacity of perforated shearwalls. Previously, the program implemented only the table.
The program actually implements an equation that was used to generate Table 18.104.22.168. This equation is
Co = 1 /( 3h0/h - 3h0/h * ∑Li / Ltot + ∑Li / Ltot )
where ho is the maximum opening height and the other variables are as defined in the SDPWS. Equations 4.3-5 and 4.3-6 are
Co = r Ltot /(3-2r)∑Li ; r = 1 / (1 + Ao / h∑Li)
Where Ao is the total opening area. These equations are evidently quite different and yield different results. Either method is acceptable.
There is no provision in the program to allow for situations where there is no sheathing above or below the opening that is included in the definition of Ao. If you encounter this situation, just enter larger opening sizes.
The hold-down database has been updated to include the most commonly used hold-downs from the most recent Simpson’s product catalog.
a) Species Categories for Hold-down Capacity (Feature 181)
The hold-down database now has separate capacities for the categories of species of the studs that the hold-downs are attached to. These species groups are Douglas Fir-Larch / Southern Pine (DF/SP) and Spruce-Pine-Fir / Hemlock-Fir (SPF/HF).
i. Determination of Species Category
The program identifies the species group to be used by the specific gravity of the stud material. For Specific Gravity less than or equal to .49 the program uses SPF/HF values, and above 0.49 it uses DF/SP values.
ii. Materials Below Minimum Threshold
The Simpson data do not apply to materials with a specific gravity less than 0.42. For visually graded lumber, the S-P-F (S) species, and for MSR/MEL, the Western Woods and Western Cedars species and the Engelmann Spruce/ Lodgepole Pine grades with E less than 1.5 all have specific gravities less than 0.42.
If one of these materials is used, the program applies the SPF/HF hold-down capacities, and issues a warning note under the Hold-down Design table.
iii. Materials Above the Maximum Threshold
General Note f of the Simpson Wood Construction Connectors 2015-2016 catalog says “the species of lumber used shall have a specific gravity not greater than 0.55 as determined in accordance with the NDS.” No visually graded lumber species have a S.G. greater than .55, but for MSR and MEL Doug Fir-L (N) grades with E of 2.3 or greater and Southern Pine grades with an E of 1.8 or greater have specific gravity greater than 0.55. Shearwalls allows these materials without giving you any warning, so it is recommended that they not be selected for shearwall design.
iv. Hold-down Database Editor
A new column has been added in the Design properties list (formerly Displacement) for DF/SP capacities, and the existing column has been renamed to indicate SPF/HF.
b) ASD Deflections
The hold-down database now has separate deflection values for Allowable Stress (ASD) and Strength design. Previously it had only strength-level deflections. ASD deflection values are now used for deflections from wind loads to distribute forces to the shear segments in the main wind force resisting system (MWFRS) for shearwall design.
Strength-level deflections are still used for seismic design, and for the newly added serviceability wind loads used for story drift limit calculations.
i. Hold-down Database Editor
A new column has been added in the Design properties list (formerly Displacement) for ASD deflections, and the existing column has been renamed to indicate Strength.
c) Existing Projects
The hold-down names are all different than the ones in the previous database, so none of the standard hold-downs in existing project files are in the new database. When Shearwalls opens your old project files, and detects a hold-down that is not in the database, it will add that hold-down to the new database.
i. Species Category and ASD Deflection Values
Since the old database did not have different capacities based on species group, and did not have ASD deflections, the program assigns the old SPF/HF capacity value to DF/SP as well, and the old strength-level deflection to ASD deflection. So, after loading a project file from previous versions, we recommend you open the hold-down database editor and revise the DF/SP capacities and ASD deflection values to the correct ones from the Simpson product catalog.
ii. Custom Hold-downs
It is possible that you have already edited the old database to include at least some of the hold-downs in the new database. However, the names you would have used are likely to be slightly different than the standard names, so these hold-downs will be duplicated when you load your project files. You can use the hold-down database editor to remove the duplicate hold-downs, making sure that the names of the remaining hold-downs match the ones in your project files.
Some of the out-of-plane wind load capacities for C&C design of sheathing from SDPWS Table 3.2.1 have changed:
- 3/8” sheathing, parallel, 24” spacing: 25 to 30 psf
- 7/16” sheathing, parallel, 24” spacing: 30 to 35 psf
- 15/32” sheathing, parallel, 24” spacing: 40 to 45 psf
- 19/32” sheathing, parallel, 24” spacing: 65 to 75 psf
- 23/32” sheathing, perpendicular, 16” spacing: 805 to 840 psf
- 23/32” sheathing, perpendicular, 24” spacing: 360 to 395 psf
- 23/32” sheathing, parallel, 16” spacing: 215 to 255 psf
- 23/32” sheathing, parallel, 24” spacing: 95 to 115 psf
a) Critical Segment Determination for Deflection-based Distribution (Bug 3191)
For deflection-based design, the program determined the critical shearwall segment for design via the largest unit (plf) force on the segment, without r egard to aspect ratio. It then applied the critical aspect ratio factor to that force, however the aspect ratio could be from one segment and the force from another.
Because narrow segments tend to deflect less and draw less force than wide ones, it happens frequently that the critical force comes from the wide segment and the critical aspect ratio from the small one.
The now determines the critical segment by dividing the force by the aspect ratio and taking the largest of these values.
b) Shear force on Segments for Capacity based Distribution (Bug 3189)
For capacity based distribution within a line, the design shear force for each segment on a wall was based on the segment with the critical aspect ratio, so that an entire wall has the same shear unit (plf) shear force, rather than assigning different forces to each segment based on the factored capacity of each segment.
This had a conservative affect on shearwall design. Although the critical segment for design (the one with the highest aspect ratio) was using the correct capacity, it was drawing too much load because too little was apportioned to the non-critical segments.
This also had an affect on the force distribution for story drift deflections, however how it affected the maximum deflection on the line depends on other factors and it could be conservative or non-conservative.
It also affected hold-down forces. Those at the ends of the segments with non-critical aspect ratios were too lightly loaded, and the others too heavily loaded.
These problems have been corrected.
c) Perforated Shearwall Factor for Hold-downs
The program was not applying the perforated shearwall factor Co to the hold-down force T determination in Eqn. 4.3-8 in SDPWS 22.214.171.124.2. This has been corrected.
d) Persistence of "Design as Group" Checkbox in Standard Wall Mode (Bug 3022)
When you unchecked the Design as Group checkbox in Standard Wall mode, the change was not retained when selecting another standard wall or exiting the box, making it impossible to specify that standard walls are not designed as a group. This has been corrected.
e) Aspect Ratio Factor for Perforated Walls (Bug 3178)
An example was presented to us in which the program did not apply SDPWS 126.96.36.199 stating that the height-to width factor of 2b/s be applied to the entire perforated wall based on the narrowest segment in the wall.
In this example, the narrowest segment is 3 feet in an eight-foot height wall, leading to a factor of .75. This factor does not appear in the shear results table, and the, and the 200 plf wall strength reduced only by the .61 Co factor, yielding 123 lbs, when it should also have been reduced by the aspect ratio factor for a strength of 91 lbs.
This behaviour could not be replicated for other examples, and whatever may have caused this instance was corrected by the fact that aspect ratio factors are no longer applied directly to perforated walls for SDPWS 2015.
f) Failure to Apply Aspect Ratio (Bug 3180)
An example was presented to us in which the program did not apply the aspect ratio factor 2bs/h from SDPWS Table 4.3.4 Note 1. For a 3-foot wide segment in an 8-foot wall, which should have a factor of .75, no factor was shown in the shear results table and the design capacity was not reduced; it was 200 plf rather than the expected 150.
This behaviour could not be replicated for other examples, and this instance was corrected by the extensive changes to the implementation of aspect ratio factors for SDPWS 2015.
g) Force Distribution due to Unsorted Openings (Bug 2099)
Occasionally, after a complex set of user interface operations, wall openings could become unsorted internally and skew the distribution of forces on the shearline, also affecting shearwall design. This has been corrected.
h) Dead Load Contribution to Hold-down Forces for Rigid-Only Design (Bug 3153)
Hold-down forces components due to dead loads were not created when designing for rigid diaphragm forces only, that is, when flexible diaphragm analysis is turned off in the Structure view. These force components did not appear in the Hold-down Design table or in Elevation View, and the deflection analysis and design of hold-downs did not include the counteracting effect of dead loads. This has been corrected
i) Vertical Accumulation of Hold-down Forces from Different All-heights Load Cases (Bug 3105)
When the critical shearline force acting on different levels came from different all-heights load cases (Case 1, Case 2, or Minimum), the hold-down forces were not accumulating vertically.
This created two smaller hold-down forces on the levels which were drawn on top of each other in Elevation view, instead of a single hold-down force with the combined value.
These smaller hold-down forces also appeared in the hold-down results table, and the hold-down device was verified against each of these smaller forces rather than the larger combined force. One of the hold-down forces, selected at random, was used for deflection design, creating a lower deflection than if the full hold-down force was used.
These problems have been corrected.
j) Roof Height Used for Approximate Period Calculation (Bug 3199)
The program was using the eave height to calculate the approximate period Ta in ASCE 7-10 Equation 12.8-7); however according to the definition of hn in 11.3 Symbols, the mean roof height should be used.
This error does not affect the seismic base shear calculations unless the calculation for Csmax (ASCE 7-10 equations 12.8-3 and 12.8-4) governs.
Note that the definition for hn changed between the ASCE 7-05 and ASCE 7-10 editions, and the program was not updated for the change. It has now been corrected.
k) Manually Input Loads Entered after Case 2 Wind Loads (Bug 3181)
A manually input load of any type entered after a Case 2 wind load would not be detected by the load distribution system and not contribute to design or appear in the load and force drawings.
This has been corrected.
l) Shear Capacity in Elevation View (QA Bug 42)
The capacity shown in Elevation View under the shearwalls for All shearwalls was including the average of the aspect ratio factors for all segments on the wall, which is both confusing and lacking in design significance. It now shows the unfactored capacity. The factored capacity is shown for the Critical Segment below.
m) C&C Sheathing Capacity in Elevation View Table (QA Bug 42)
The C&C sheathing capacity shown in Elevation View under the shearwalls was mistakenly including the aspect ratio factor, which is intended for in-plane shear design and does not apply to out-of-plane C&C design. This has been corrected.
n) OSB and GWB in Wet Service Conditions (Bug 3000)
Oriented strand board (OSB) and gypsum wallboard (GWB) are no longer allowed for wet service conditions. When you try to add one of these materials to a structure for which wet service conditions is set, the program disallows the entry. If such materials exist in the structure, the program disallows entry of in-service moisture content greater than 19%.
o) Drag strut Forces on Perforated Walls with Zero Length Segments (Bug 2982)
Perforated walls which contain a wall segment with zero length were showing nonsensical values for drag struts that are located after the zero-length segment. Zero length segments occur when an opening is placed at the very beginning or very end of a wall.
The program now implements the story drift limitations from ASCE 7-10 Commentary Appendix C Serviceability Considerations, CC.1.2 Drift of Walls and Frames (page 580).
a) Drift Limits
ASCE 7 CC.1.2 suggests limits in the range of 1/600 to 1/400 of the storey height. A design setting has been added to allow you to enter the drift limit to be imposed.
The storey height h used is the wall height plus the joist depth on the same level.
b) Wind Speed
The wind speed to be used is from the maps in Figures CC1 to CC4 of ASCE 7-10, corresponding to mean recurrence intervals (MRI) of 10, 25, 50, and 100 years, respectively. It is up to the designer’s judgement as to which of these to choose.
A new data group has been added to the Site Dialog called Wind speed, which includes the input MRI (serviceability) to allow you to enter the value for your area from these maps. The existing input for shearwall design has been renamed Basic (MWFRS).
The default for new files is 100 mph.
Unlike the design wind speed, the program does not currently allow you to save a value as default for new files; it must be reset for every project.
c) Load Combination
The load combination employed is D + 0.5L + Wa, from ASCE 7 CC.1.2.
This combination is used for serviceability calculations only, i.e., for the in-plane shearwall deflection to be compared to drift limits. It is not used for the deflections used to distribute loads for shearwall design; these now use the ASD load combination from 2.4.1, 0.6W + 0.6D. (Previously strength-level load combination was used, see item 3 below for a description of that change).
i. Wind Load Wa
The wind load Wa is derived from the serviceability wind speeds using the same provisions that are used to generate wind loads for shearwall design from ASCE 7 Chapters 26-28. The only difference is the wind velocity used to create pressures in 27.3.2 and 28.3.2.
In determining deflections, Wa is used for:
- the segment force v, including v used to calculate overturning hold-down force
- the wind uplift component of the hold-down force
- the overturning component of hold-down forces transferred from upper stories.
ii. Dead Load D
The dead load factor is 1.0, as opposed to the 0.6 ASD factor for MWFRS deflections used for force distribution for shearwall design. These factors are for dead loads counteracting the wind overturning hold-down force
iii. Live Load L
The 0.5L component is not considered, as the program does not include live loads. In any event, it is not clear that these loads are permitted as counteracting loads or are intended only to increase deflections, as one cannot depend on the occupancy load to be present.
d) Shearline Forces
The program does not create a separate load case to determine shearline forces for drift-limit deflection; instead, it uses the ASD shearline forces multiplied by a factor α representing the difference in wind pressures between those used for serviceability and for MWFRS design, as well as the difference in load combination factors. Since wind pressures are given in ASCE 7 27.3.2 and 28.3.2 by P = d * Kz * Kd * Kzt * V2 * G * Cp, in which all terms except for V are the same, this factor is
α = PSERV / PMWFRS / 0.6 = (VSERV / VMWFRS)2 / 0.6
i. Rigid Diaphragm method.
The assumption that shearline forces are proportional to wind pressures is not strictly true for the rigid diaphragm method due to nonlinearity in the torsional distribution to shearlines. However, for typical asymmetric buildings with a significant torsional component, the difference in shearline forces using this approximation compared with generating and distributing reduced wind loads Wa is less than 1%.
ii. Comparison with ASD Forces
The program makes a separate set of defection calculations for ASD design of shearwalls, to distribute shearline forces to the shear resisting elements. Unlike serviceability deflections, the wind speeds used to generate the force for these deflections depend on Risk category; however, they do not depend on a discretionary selection of recurrence interval (MRI).
Using the southern tip of Florida as an example, the factored forces resulting from serviceability wind speeds and load combination range from 34% of the ASD forces for Risk Category III/IV buildings at 10-year MRI to 130% of ASD forces for Risk Category I at 100 year MRI. For a typical case of Risk Level II (Normal) at 50-year MRI, serviceability forces are 87% of ASD forces.
iii. Distribution to Segments within Line
The process of distributing forces to segments in a line such that they equalize deflections is performed independently for serviceability wind forces. Because some of the deflection components are constant with respect to v, one cannot rely on the distribution of forces achieved with the MWFRS wind speed and just factor each segment force by α, as we do with shearline forces. If capacity-based distribution to segments is used, it is possible to do so.
e) Calculation of Ga for the 3-term Deflection Equation
As the program now gives you the option of using the 3-term deflection equation from SDPWS 4.3-1 (see item 2 below), a question arises as to what apparent shear stiffness Ga to use for serviceability wind loads. The SDPWS publishes Ga values for seismic design only, and does not offer guidance on wind loads.
We have implemented a procedure for serviceability wind loads that is analogous to the procedure for seismic loads using the SDPWS Equation C4.2.2-3. Instead of using 1.4 vs,, we use α vw where α is defined in the previous subsection. This procedure applies to wood structural panels only; for other materials, we use unfactored vw, which results in a Ga close to what is published in the SDPWS for seismic design. The formula for Ga is therefore
Although this procedure was developed by WoodWorks it has been approved by AWC.
i. Background and Rationale
The Ga value is calculated for seismic design using is a linear approximation of the 4-term equation arrived at by combining the multiplicands of v in the 3rd and 4th terms into an “apparent” shear stiffness.
The linearization is achieved by setting all non-linear instances of the shear force v in Ga to the value at shearwall capacity, vs. This means that the 3-term and 4-term equations are the same at full shearwall capacity, and ensures that the linear 3-term deflections are conservative with respect to the non-linear 4 term ones for all shearwalls that have sufficient capacity to resist the applied shear force. Refer to SDPWS figure C4.3.2 for a graph of this linearization process.
For seismic design an adjustment
is necessary, because deflections are calculated using v’s for Strength-level
design, with a load combination factor of 1.0, however the shearwall
capacity vs is for ASD design, which has a factor of 0.7. Therefore,
to ensure that the 3-term approximation is conservative for all shearwalls that pass ASD design, the value 1.4 vs is
used. (For historical reasons, SDPWS rounds the factor to 1.4 rather than using
1 / 0.7, which converts ASD forces to strength-level forces).
For serviceability wind loads, the v’s used for deflection calculations are the ASD design forces multiplied by α, which includes the serviceability wind speeds and the serviceability load combination factor. Therefore, the serviceability v at the point at which the shearwall is fully loaded is α vw.
ii. Comparison with Published Ga
Some users may not be comfortable with using Ga values other than those published in the SDPWS for seismic design, especially since they are the same Ga values used, by coincidence, for MWFRS wind design with wood structural panels. Although Ga is published in SDPWS as a physical parameter, it is not a physical property of the sheathing in the same sense as Gvt, which is used in the 4-term equation; it is also an artifact of the linearization procedure used to convert 4-term to 3 term, in that it is highly dependent on the point chosen to intersect the 3-term and 4 term equation.
If the published Ga were to be used, in most cases it would cause the 3-term to intersect the 4-term at a point far above the point at which shearwalls are fully loaded. As an example, for a shearwall that is 80% loaded, for 10 year MRI this causes shear/slip deflections for the 3-term equation to be 2-3 times higher than they would be using the α factor. For a typical case of 50 year MRI, Normal risk level, the deflections are 28% higher. This would be problematic as designers often have difficulty meeting stringent drift limitations.
For 100 year MRI, the equations intersect below the point that the shearwall is fully loaded, so that the 3-term deflections would be non-conservative with respect to 4-term by as much as 40%.
For fiberboard and gypsum wallboard, the nail slippage in the 4-term equation is constant, and the 4-term equation is not in fact non-linear. The effect of Ga the 3-term equation is to vary the shear component deflection from 0 to the deflection at shearwall capacity, rather starting at the constant shear nail slip value. The arguments in the previous sections therefore do not apply, and we were instructed by AWC to use the published Ga values for seismic design for these materials.
f) Hold-down Displacement
When calculating hold-down displacements, the strength-level values from the hold-down database are used, as the wind load combination factor 1.0 is the same as it is for strength-level design. Note that ASD values are now used for MWFRS deflections.
i. Design Results
Refer to section N below for changes to the Design Results output arising from this feature.
ii. Log File
Because serviceability shearline forces were derived from ASD forces, as described above, serviceability wind loads were not generated and do not appear in the log file. Torsional analysis for serviceability wind loads is not performed independently and does not appear either.
h) Plan View
Because serviceability shearline forces were derived from ASD forces, as described above, serviceability wind loads were not generated and do not appear in the Plan view when Generate Loads or Loads and Forces is selected. Neither is there an option at present to show the forces derived from serviceability wind loads in Loads and Forces view.
Shearwalls now offers the choice of using the linear 3-term deflection equation from SDPWS 4.2-1 and the non-linear 4-term equation from C4.3.2-1. Previously only the 4-term equation was implemented.
The 3-term equation is a linearization of the 4-term equation, arrived at by combining the shear and nail slip equations in the 4-term equation using an “apparent” shear stiffness Ga. The linearization is achieved by setting the non-linear occurrences of shear force v to the shear capacity of the shearwall to render them constant. It is therefore identical to the 4-term equation when the shearwall is at capacity, conservative when below capacity, and non-conservative for shearwalls that are overstressed for design anyway. SDPWS Figure C4.3.2 shows this in graphical form.
The four-term equation was originally implemented in Shearwalls because it is more accurate and because the SDPWS does not publish Ga values for wind design. However, the process of equalizing deflections on the shearwall segments by adjusting the forces apportioned to each segment sometimes does not converge due to the non-linearity of the 4-term equation, whereas the 3-term equation always converges to a solution. Also, some users are more comfortable using the 3-term equation because it is in the main body of the SDPWS, whereas the 4-term equation is in the Commentary.
b) Design Setting
A Design Setting has been added to allow you to choose between these two methods. It is recommended to use the 4-term equation, but switch to the 3-term if using the deflection-based force distribution method and one or more of the shearlines do not show the same deflections on each loaded shearwall segment in the line.
Note that SDPWS commentary C4.3.2 cautions against mixing the two methods in the same design, as it can adversely influence force distribution based on relative stiffness. This is true within a line, and possibly distribution to shearlines if the rigid distribution method is used. For a future version we will consider allowing the program to automatically change from 4-term to 3-term on individual shearlines if non-convergence is detected, especially using flexible distribution; however, for Version 11, the switch must be made manually and for all shearlines in the structure.
c) Wind Design
The SDPWS lists Ga values for seismic design only, and gives design examples using the 3-term equation and showing how to calculate Ga for only for seismic design. However, Shearwalls allows this method for wind design, with the adjustments to the calculation procedure given below.
d) Deflection Calculation
The following terms in the two-term equation
are replaced by
i. Ga Calculation, Seismic
The calculation of Ga for seismic design uses the formula
The factor 1.4 ≈ 1/0.7 ensures that the v
In most cases, the value of Ga is the same as that listed in Table 4.2B, but it may be slightly different because the use of the equation allows us to consider the number of plywood plies when evaluating Gvtv., whereas note 3 of Table 4.2B approximates this effect by applying a factor of 1.2.
ii. Ga Calculation, MWFRS Wind
For wind deflections for MWFRS force distribution, the same expression is used without the 1.4 factor, because we now evaluate deflections with ASD forces and there is no need to convert from ASD design to Strength deflections. The formula for Ga is
For wood structural panels and fiberboard, this results in the same Ga values as for seismic design because the shearwall capacity vw = 1.4 vs. It is important to note that this is merely a coincidence; the difference in capacity for wind vs. seismic is for unrelated reasons pertaining to a historical increase in design wind loads related to test strengths. The increase was not applied to other materials such as gypsum wallboard, and these have different Ga values for wind vs. seismic design.
iii. Ga Calculation, Serviceability Wind
Shearwalls 11 includes a new set of serviceability deflections for story drift determination, described in the preceding section, which also includes the calculation of Ga for serviceability wind forces.
iv. Unblocked Factor
The unblocked factor Cub is applied only to the v value in the main deflection equation. not the vs and vw values in the calculation of Ga. This is consistent with SDPWS Eqn. C188.8.131.52-2, where it is shown that dividing v by Cub is equivalent to factoring the whole shear stiffness Ga by Cub.
v. Capacity Increase for 3/8” and 7/16” Sheathing on Unblocked Shearwalls
As per Commentary C184.108.40.206, the capacity Increase for 3/8” and 7/16” sheathing under certain framing conditions from Table 4.2A Note 2, is not applied to vs or vw for unblocked shearwalls for the purpose calculating Ga.
Refer to N.8 below for changes to the Deflection table arising from this feature.
On the advice of AWC, Shearwalls now calculates deflections to distribute forces to the main wind force resisting system for shearwall design based on the ASD load combination 0.6D + 0.6W from ASCE 7-10 2.4. Previously Strength-level deflections were used, using 0.9D + 1.0W, from ASCE 7-10 2.3, because they are required for seismic design by 12.8.6 and the ASCE 7 does not offer guidance on wind design.
a) Force Calculation Changes
The wind load factor changes from 1.0 to 0.6 for the shearline force v, for wind uplift hold-down force, and for the effect of hold-down forces from upper levels.
The dead load factor changes from 0.9 to 0.6 for the counteracting dead load component of hold-down force.
b) Hold-down Database
Previously the hold-down database had only strength-level deflections. It has been expanded to include ASD deflections to be used for ASD wind design. Strength-level deflections are retained for seismic design and for serviceability wind loads for story drift calculations.
To implement the new SDPWS provision 220.127.116.11, if there is fiberboard on either side of a wall segment with an aspect ratio greater than 1:1, the total deflection for the segment is multiplied by (h/b) ½.
If there is any fiberboard in the structure, the application of this factor is mentioned in the Legend to the Deflection table, however the actual value of the factor is not listed in the table.
a) Shearwall Capacity Hold-down Method in the Calculation of Deflections (Bug 2999)
If you specify via the Design Settings that shearwall capacity is to be used as the design force for hold-down design, this value was also used to determine the hold-down component of shearwall deflection. As this is not the intent of the use of shearwall capacity to ensure sufficient hold-down strength, the calculation for deflection now always uses applied force to determine hold-down displacement, regardless of the design setting for hold-down forces.
b) Tolerance in Equalizing Deflections (Change 227)
Occasionally, warnings appeared indicating the program had not equalized deflections on the shearline, when the Design Results output showed identical deflections along the line. This was because the tolerance for equalizing deflections internally was 0.01% of the deflection value, which is unnecessarily stringent. It has been changed to .5%”, which ensures that when deflections are not equalized to that level, it is apparent in the output table.
c) Deflection Equalization Failure (QA Bug 18)
Occasionally, for two-sided shearwalls, the program would show v, vmax, and Critical response values in the Shear results table as dashes or blanks, even though there is a total force V on the wall in question.
This was due to an intermittent failure in the process equalizing deflections on either side of the wall, and has been corrected.
Extensive changes to several of the Design Settings was necessitated by the following changes to the SDPWS:
the Aspect Ratio Factors in SDPWS 2015 4.3.4 and adjustments in 18.104.22.168.1 are now identical for wind and seismic design, whereas in SDPWS 2008 Table 4.3.4 the factors applied only to seismic design for wood structural panels, and differed between seismic and wind for fiberboard.
For capacity-based force distribution, gypsum-based materials or lumber sheathing are no longer allowed, as per SDPWS 2015 22.214.171.124.1, and for wood structural panels and fiberboard, an “adjustment” is applied to narrow segments, rather than the Aspect Ratio factors in 4.3.4 that apply to deflection-based distribution.
The SDPWS now recognizes only capacity-based and deflection based force distribution methods.
The SPDWS C126.96.36.199 clarification of the definition of “similar materials and construction” along a shearline
The changes to the design settings also, present the options more understandably, use the current SDPWS terminology, implement SDPWS provisions that were previously omitted, and simplify special cases such as the treatment of fiberboard.
1. Shearwall Rigidity Settings
a) Data Group Name
The data group previously called Shearwall rigidity per unit length…