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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 10.0 and may not reflect current program behaviour.
The program previously assumed that there would be no periods greater than 0.5, so the program did not check for the condition Ta > 0.5 or disallow irregularities of Type 1-6 as per 4.1.8.7.(1)(c).
However, a period of twice the one calculated by empirical formula 4.1.8.11.(3)(c) is allowed by 4.1.8.11.(3)(d)(iii), so any height above that corresponding to T = 0.25 using the formula, or 8.5 meters, could have a Ta > 0.5. In practice, 5- and 6-storey structures now supported by Shearwalls often do have periods in this range when calculated using methods such as the Rayleigh quotient.
The following applies if Irregularities Type 1, 2 ,3, 4, 5, or 6 exist and if IEFaSa(0.2) >= 0.35:
if T >= 0.5 in the direction(s) for which the irregularity exists, the shearlines and direction(s)s that have these irregularities appear in the "Fails for" column.
If T >= 0.5 in at least one direction for which the irregularity exists, a red warning message appears above the table indicating that design has failed due to the irregularity. The message saying that the program does not check for T > 0.5 has been removed.
If T >= 0.5 in at least one direction for which the irregularity exists, a screen warning message appears indicating that design results are not valid.
Notes appear below the table indexed to the irregularities saying that seismic design is not allowed using the Equivalent Static Procedure when T > 0.5, and it is if it is less than or equal to 0.5.
If T >= 0.5 in at least one direction for which the irregularity exists, it triggers the note in the Design Summary saying that at least one irregularity violates design code provisions.
The program now detects the Type 1 Irregularity – Vertical Stiffness, which occurs when the lateral stiffness of a storey’s SFRS less than 70% of that of an adjacent storey, or 80% of the average of the three storeys above and below.
In each direction, for both rigid and flexible diaphragms, the program determines the stiffness of all wall segments on the level using the same procedure by which it determines the stiffness for Irregularity 4 – In Plane Discontinuity. It will then sum all those stiffness values.
If the stiffness on any level is less than 70% of the stiffness on the level above or below, than the irregularity exists.
For those levels with 3 storeys either above or below (levels 1 and 4 in a 4- storey structure; 1, 2, 4, and 5 in a 5-storey structure, and any level in a 6-storey structure), the program determines average of the 3 storeys either above or below the level, and if stiffness on the level under consideration is less than 80% of that value, the irregularity exists.
For the adjacent level stiffness, the Irregular for… column in the Seismic Irregularity Table shows the level with the reduced stiffness followed by the stiffer level e.g. 3,4.
For the average of 3 levels, it shows the reduced stiffness followed by the stiffer levels as e.g. 4,1-3
The Direction shows E-W, N-S, Both, or None.
If there is a weight irregularity and T>=0.5 for at least one direction, and IaFaSa(0.2) >= 0.35, the storeys appear in the Fails for column
The note saying it is irregularity detection is not required for because it is not a post-disaster building has been removed.
The existing notes about the relevance of IEFaSa(0.2) >= 0.35 or < 0.5 and T < 0.5 are included when irregular. If T >= 0.5 a new note says that Equivalent Static Procedure is not allowed.
If irregular, T >= 0.5 in at least one direction, and IEFaSa(0.2) >= 0.35, a screen warning message appears indicating that design results are not valid, a red warning message appears above the Irregularities table, and the Design Summary says that at least one irregularity violates design code provisions.
The description of the irregularity below the table gives the 70% rule and 80% rules and explains the table columns.
The program now detects the Type 2 Irregularity – Weight (mass), which occurs when a level is 1.5 x more massive than an adjacent non-roof level, or a roof is 1.5 x as massive as its adjacent level.
Table 4.1.8.6 refers to a storey, which is defined in NBC Division A, 1.4.1.2 as the distance from the top of one floor to the top of the floor above it. The roof is considered a separate storey.
On the other hand, the levels that are defined for apportioning seismic load are defined from the middle of the wall on one level to the middle of the walls on the level above. A roof is considered part of the upper level.
For irregularity detection, the program collects all the masses that are tagged as being on level 2, for example, but come from the lower portion of level 3, and includes them as storey 3 loads. It excludes masses from the roof and gable ends, which are on the uppermost level, from the upper storey, and creates a separate storey for these.
For multi-block structures, for mass from roofs on blocks with fewer levels than the highest block, the roof is added to the mass of the level above the highest storey on the block. For example, if Block 1 has 2 storeys and block 2 has 4 storeys, a roof on block 1 will is part of level 3.
Flat roofs and ceilings are part of the uppermost storey of the block they are on, not the roof level.
Snow masses are not included among the weights for this purpose.
The Irregular for… column in the Seismic Irregularity table shows the heavier storey followed by the light storey, e.g. 3,4. The direction is always Both. If a heavy roof is one of the storeys, the word "Roof" is used.
If there is a weight irregularity and T>=0.5 for at least one direction, and IaFaSa(0.2) >= 0.35, the storeys appear in the Fails for column
The note saying it is irregularity detection is not required for Ta less than 0.5 has been removed. The existing notes about the relevance of IEFaSa(0.2) >= 0.35 or < 0.5 and T < 0.5 are included when irregular. If T >= 0.5 a new note says that Equivalent Static Procedure is not allowed.
If irregular, T >= 0.5 in at least one direction, and IEFaSa(0.2) >= 0.35, a screen warning message appears indicating that design results are not valid, a red warning message appears above the Irregularities table, and the Design Summary says that at least one irregularity violates design code provisions.
The description of the irregularity below the table gives the 150% rule, defines a storey, and explains the table columns.
Research into the intention of NBC 2015 4.1.8.15.(5) ( NDS 2010 4.1.8.15.(4)) has inspired a re-evaluation of the approach taken by Shearwalls to this provision. This clause states that elements supporting a discontinuous wall are to be designed for forces equal to the lateral capacity of the SFRS components they support rather than calculated forces. The intention is to protect the gravity force resisting system from forces due to lateral loading, for example a lintel above an opening that supports vertical element such as a column carrying a hold-down force at the end of a discontinuous shearwall on the level above the opening. In such a case, the column, lintel, hold-down, and other connections are to be designed using the capacity of the discontinuous wall.
Shearwalls previously applied this irregularity for Irregularities Type 3 - Vertical geometric, Type 4 - In-Plane Discontinuity (offset), Type 4 - In-Plane Discontinuity (stiffness) and Type 5 - Out-of-plane Offsets, The rationale for Types 3 and 5 was that a discontinuity must exist somewhere for these irregularities to exist, and for Type 4 - In-Plane discontinuity (stiffness) that the NBC 2010 Commentary J-205 (NBC 2015 J-208) referred to Type 4 irregularities in general.
Shearwalls now applies this provision only for Type 4 - In-Plane Discontinuity (offset) and Type 5 - Out-of-plane Offsets. Shearwalls detects an in-plane offset whenever wall ends do not line up on adjacent floors, which is exactly the type of discontinuity this provision is meant to address. Type 5 discontinuities occur when there is no wall below a wall on the level above, which also creates a discontinuity at wall ends.
Stiffness irregularities are irrelevant to the intent of this item so Type 4 - In-Plane discontinuity (stiffness) is no longer included. And although Type 3 - Vertical geometric implies a discontinuity must exist somewhere, it is a general, statistical check which cannot be used to identify where action must be taken. If Type 3 exists, then a Type 4 or Type 5 must also exist somewhere, so the situation will be handled without the need to include Type 3 in the solution.
The program previously reported a failure due to these irregularities if the capacity of the entire SRFS on the floor below the one with the discontinuity was less than the capacity of one with the discontinuity. This was based on a misconception and has been removed from the program.
The program no longer includes discontinuous shearlines in the Fails for column of the Seismic Irregularities table for this reason, nor does it issue screen warnings for this failure or place a red failure message above the table. The notes below the table have also been modified.
When an irregularity was detected, the program automatically used shearwall capacity as the design hold-down force on all shearwalls on both the level with the irregularity and the level below. This is an overly conservative approach, and this automatic procedure has been removed from the program until we can develop an algorithm to identify and strengthen only those hold-downs that require it.
When an irregularity was detected, the program automatically used shearwall capacity as the design drag strut force on all shearwalls on the level below. Instead, the program should add the additional force due to capacity-based design on the floor above as a surcharge to the diaphragm shear force used to calculate drag struts on the floor below. The automatic strengthening of drag struts has been removed until we can develop such a procedure.
The need to identify irregularities to apply the automatic strengthening of hold-downs and drag struts necessitated an additional iteration of force distribution and design in Shearwalls. This has been removed, which should lead to somewhat faster design results.
All screen warnings have been modified to indicate that you must manually strengthen hold-downs and drag struts at specific locations, rather than informing you that the program has done so. The notes below the Irregularities table have been similarly modified.
The asterisk beside the Design Settings Drag strut / Hold-down forces based on … Applied loads has been removed, along with the note saying that shearwall capacity is used for discontinuities as per 4.1.8.15.(4).
Due to the non-linearity in the nail deformation term of the equation for deflection for shearwall deflection from 11.7.1.2, shearwall stiffness decreases as applied force increases. As a result, Shearwalls previously identified a Type 4 In-Plane Discontinuity (stiffness) in NBC 4.1.8.6 based on a lower-storey shear resisting element having less stiffness than an upper storey one even when walls on the two storeys had identical construction.
As structural analysis for most materials assumes a linear stiffness relation v = K δ, where v are forces, δ deflection, and K a constant stiffness matrix, we do not believe it was the intention of NBC 4.1.8.6 to consider identically constructed storeys as having differing stiffness. The program therefore uses the 3-term linearization of the deflection equation introduced in this version (see ), to determine the deflections for Type 1 - Vertical Stiffness and Type 4 – In-plane Discontinuity (stiffness) irregularity detection. It does so even when the non-linear 4-term equation is used for deflection analysis for force distribution and storey drift.
If the you have selected the 4-term deflection equation option in the design settings (the default), an additional design iteration will be inserted before the existing iterations, using the 3-term deflection equation, for the purpose of detecting Type 1 and Type 4 (stiffness) irregularities. Another iteration is then performed for final design of the shearwalls using the non-linear 4 term equation, during which all other irregularities are detected.
Testing revealed that small, unwanted differences in stiffness still occurred for identical shearwalls on adjacent levels. A comparison tolerance of 1% was added which eliminated these occurrences.
The description of the Type 4 – In-plane Discontinuity (stiffness) irregularity beneath the Irregularity table has been modified to reflect this procedure.
Irregularity names in the Irregularity table have been modified to conform more closely to the nomenclature in Table 4.1.8.6. In screen messages they have been expanded to show a less abbreviated name, and in the descriptions below the Irregularities table, the full name as it appears in Table 4.1.8.6 is shown.
The format of references to NBC provisions in the table has been modified to conform to NBC protocol, e.g. 7-1c is now 7(1)(c). Compound references change from e.g. 10-1,2b to 10(1),(2)(b).
Also changed comma between two Sentence references to a semi-colon, to distinguish from comma between Clauses.
The Detected by column has been removed as all relevant irregularities are now detected by the program.
The screen message indicating an Irregularity 8 was detected referred to an IESaFa(0.2) value of 2.0 when it should have been 0.2. This has been corrected
The notes pertaining to Weak Storey Irregularity Type 6 have been reorganized and improved, giving references to NBC 4.1.8.10.(1) and 4.1.8.10.(2)(b).
A reference to NBC 4.1.8.10.(2)(a) has been added to the note about post-disaster buildings.
The notes that include IEFaSa(0.2) >= 0.35 or < 0.35 N now include references to NBC 4.1.8.7.(1)(a), 4.1.8.6.(3) and Commentary J-122.
NDS 2010 Commentary J-156 (NBC 2015 J-150) has been added for Type 7 Irregularities.
NDS 2010 Commentary J-207 was a mistake; it has been changed to J-205.
NDS 2010 Commentary J-127 was a mistake; it has been changed to J-128.
NDS 2010 Commentary J-177-9 was a mistake; it has been changed to J-171-3.
A new provision 4.1.8.10.(4) has been added to the NBC disallowing Irregularities Type 4 In Plane Discontinuity and Type 5 Out-of-plane offsets for 5- and 6-storey structures when IEFaSa(0.2) >= 0.35.
This had already been implemented in Shearwalls based on an identical provision in the British Columbia Building Code (BCBC). The note at the bottom of the Irregularities table and the screen message that appears for this condition have been updated to refer to the NBC and remove references to British Columbia.
In addition to the changes to the Load Generation Details output described elsewhere due to new or changed features, numerous small formatting improvements and insertions of key information have been made. The following gives the more important changes:
The Importance factor in the Site Information dialog for Hazardous importance category, which is a value you can override due to Commentary J-110, would revert to the default value of 1.3 when the Site Parameters Dialog was re-opened. This value was then used for design unless it is changed.
This has been corrected and the input of importance factor now persists.
The program was basing the failure criterion of Seismic Irregularity Type 6 – Weak Storey on a value of IEFaSa(0.2) > 0.12 when it should have been 0.20 as per 4.1.8.10.(1).
Seismic Irregularity Type 7 was not amongst the irregularities that provoked a failure due to NBC 4.1.8.10.(2).(a) for post-disaster structures, but it should be. This has been corrected.
When seismic loads are selected, the Windward Corner options are now disabled. Previously the selections were available but had no effect.
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
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. Note that it is very rare that seismic forces differ in opposing directions and this set of options usually has no effect.