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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 11 and may not reflect current program behavior.
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 4.3.3.4.1, 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.
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.
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.
The aspect ratio factor from SDPWS 4.2.4.2 is no longer be applied to perforated walls, as per SDPWS 4.3.4.3. This factor for perforated walls is now always 1.0. The new "adjustments" for capacity-based force distribution from 4.3.3.4.1 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 4.3.3.5 the program now multiplies any segment lengths Li with aspect ratios between 2 and 3.5 by 2b/h, as per SDPWS 4.3.4.3. This applies to walls of any sheathing material type.
The calculation of ∑Li is modified in this manner for the following purposes:
The calculation of Co using SDPWS Table 4.3.3.5 and using Equations 4.3-5 and 4.3-6, which are newly implemented in Shearwalls.
The calculation of Perforated Wall tension and compression hold-down forces T and C using SDPWS Eq’n. 4.3-8 in 4.3.6.1.2.
The calculation of the in-lane force transmitted to collectors, vmax using SDPWS Eqn. 4.3-9. In 4.3.4.6.1.1. vmax is shown in the Shear Results table.
The anchorage uplift force t based in vmax in SDPWS 4.3.6.4.2.1. This force appears in Elevation View.
The deflection of perforated walls using SDPWS 4.3.2.1, both in the use of vmax and in the calculation of segment length b, which is taken as ∑Li.
The SDPWS Commentary C4.3.3.4 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 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
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.
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.
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
The clarification in the SDPWS Commentary C4.3.3.4 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 4.3.3.3 and its subsections.
The program will continue to add the sheathing capacities of opposite sides of the wall as per 4.3.3.3 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 4.3.3.3.2.
For materials of the material same class (i.e. wood structural panels, gypsum-based, fiberboard, etc.; see ), but where any material property such as nail spacing or sheathing thickness is different, the sheathing combination rule given in SDPWS 4.3.3.3.1 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.
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.
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.
Although 4.3.3.3.1 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 4.3.3.5 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 4.3.3.5. 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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
The program was not applying the perforated shearwall factor Co to the hold-down force T determination in Eqn. 4.3-8 in SDPWS 4.3.6.1.2. This has been corrected.
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.
An example was presented to us in which the program did not apply SDPWS 4.3.4.1 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.
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.
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.
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
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.
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.
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.
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.
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.
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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%.
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.