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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 changes described in this topic occur when NBC 2015 is selected as the design code edition in the Design Settings, unless otherwise indicated.
The Design setting for Wind load generation procedure has changed to Wind load generation method to avoid confusion with the static vs dynamic procedures, which are now so named officially.
The choices referring to Commentary Figures 1-7/8 and I-15 have changed to
NBC 4.1.7.5 – Other buildings
NBC 4.1.7.6 – Low buildings
In the header to the Load Generation Details file (previously part of the Log file), now states that the Static procedure from NBC 4.1.7.3 is used ( 4.1.7.3) then refers to the 4.1.7.5 or NBC 4.1.7.6 method selection.
For both 2010 and 2015 NBC selections, the program now gives the C&C procedure used, as one of
Throughout the report, all design code references now refer to 2015 provisions when the 2015 NBC option is selected.
In the header section of the Site dialog, the program now refers to the Static procedure from 4.1.7.3, and that the external pressure coefficients (Cp or CpCg) and the reference height h come from 4.1.7.5 or 4.1.7.6 according to the method selected.
In the Torsional Analysis Details file (previously part of the Log file), NBC 4.1.7.5 and NBC 4.1.7.6 are now referred to instead of I-15 and I-7.
Where it previously said Low-rise Case A, it now says Case A (NBC Figure 4.1.7.6.-A)
References to NBC 4.1.7.5 and NBC 4.1.7.6 have been added to the legend to the Shear results table.
NDS 4.1.7.1 and 4.1.7.2 clarify and solidify the conditions under which the Dynamic Procedure, which is not supported by Shearwalls, must be used. However, these Articles still do not state what height is to be used in the 4:1 height to width ratio used to classify a building as dynamically sensitive: the eave height, mean roof height, or ridge height.
This design setting giving the choice of eave, mean roof, or ridge height has been renamed to indicate that it applies only to the classification of buildings in 4.1.7.2. All other heights have been clarified by NBC 2015.
The warning message when this ratio has been exceeded has been modified to include references to 4.1.7.2.(2)(c) and 4.1.7.1.(3).
The definition reference height h, used for the calculation of exposure factors Ce and Cei has been moved from 2010 Commentary I 7 and I 8 to 4.1.7.3.(6) and 4.1.7.3.(7), respectively. Previously it was derived using an ill-defined building height H, but this height has now been precisely given in most cases as the mid-height of the roof.
The changes listed below apply to both the NDS 2010 and NDS 2015 design code selections.
A literal reading of 4.1.7.3.(6)(a) could lead to using exposure factors for buildings less than 20 meters and least plan dimension, even if Low buildings is not selected as the wind generation method. However, 2010 Commentary I-7 bases the choice of reference height on the definition in I-26 of low-rise buildings, and we do not believe it was the intention of NBC to change this.
Therefore, the use of 4.1.7.3.(6)(a) is dependent on the user selection of the 4.1.7.6 – Low buildings method, and 4.1.7.3.(6)(b) on 4.1.7.5 – Other buildings, not on the actual dimensions of the building.
Previously, the program was using ½ the eave height for all leeward surfaces (walls, roofs, and gable ends); now it uses ½ the building height, which is ½ the ridge height.
NBC 4.1.7.6.(3)(a) refers only to windward walls and no guidance is given for roofs. As the adjacent clauses refer to "surfaces", and NBC 2010 I-7 referred to windward "faces", we have assumed that the intention was that windward roof surfaces be treated the same way as walls.
Previously, the program was using the ridge height for windward roofs and gable ends. It now evaluates the pressures at increments of height, and computes a weighted average of the pressure which takes into account the diminishing width of hip panels, gable ends, and side panels on hip roofs. The height z reported is the centroid of the force distribution, i.e., the z at which the pressure is the same as the averaged pressure.
No changes were made to the calculation of reference value h for low-rise buildings’; it is still the greater of ½ the
There has been no change to the reference height for external pressures for C&C loads, it is still taken as the height at the top of the building level.
Previously, the program was using the same reference height for internal pressures Cei as for external pressures Ce. Now it uses the greater of 6 meters or ½ the ridge height, as per 4.1.7.3.(7),
In the Load Generation Details output, the reference height for internal pressures is now shown above the C&C loads table, where the mean roof height was previously shown. Mean roof height has been removed as it is not relevant to C&C loads.
The definition of the reference height in the Legend has been changed to reflect the new design code reference.
The equations for wind pressures in NBC 2015 4.1.7.3.(1) and (3) include a new topographic factor, Ct, defined in 4.1.7.4, which is algebraically identical the procedure in 2010 NBC which uses modified exposure factor Ce* and gust effect factor Cg* in place of Ce Cg, where Ce* is defined in Commentary I-14 and Cg* in Commentary I-21.
The program was modified to calculate Ct independently rather than modify Cg and Ce in order to display these values in the program output when NBC 2015 design is selected.
The NBC 2015 has made it more evident that the height used for the Ct factor is always the height above the ground, z, whereas the Ce factor may have different heights depending on the building surface and the wind load method employed. In calculating Ce* for NBC 2010, the program had been using the same reference height as used in the Ce calculation.
The program now uses the height z above the ground for both the Ct factor for NBC 2015 and Ce* in 2010. This is the weighted average height over the surface for MWFRS loads, and the height a building element at the top of a level for C&C loads.
The procedure for determining a modified gust effect factor for low-rise combined CpCg from 2010 Commentary I-21 has been removed for 2015, as it is no longer necessary.
NBC 4.1.7.3.(2) says that pressures are to be averaged over the building surface. Previously the program had been integrating C e* /Ce over the surface then multiplying with the average Ce. then calculating the gust effect factor Cg* using average Ce* and Ce.
Now the program integrates the value Ce (z) Ct(z) over the whole surface. The difference in these two approaches can be expected to be quite small.
In the Load Generation Details file (previously part of the Log file)
For both the NBC 2010 and NBC 2015 design selections, the symbols Hh, Lh, and x have been added to the Height, Length and From crest inputs. The units (ft. or m), now appear only once in the data group title.
For the NBC 2015 selection only, 2-D Ridge will be renamed 2-D Hill, to reflect the change in the design code nomenclature.
In NBC 2010, pressure coefficients Cp for buildings of any height were found in Commentary I-29 and Figure I-15; in NBC 2015 they are in a new section, 4.1.7.5, and shown in Figure A-4.1.7.5.(2) and (3) for MWFRS loads and Figure A-4.1.7.5.(4) for C&C.
Previously, the building surfaces were referred to as "walls", not they are called "faces", implying the projected surfaces of roofs are treated as walls.
Previously, the program was using the ridge height for roof loads and the eave height for walls and gable ends when determining the height-to-depth (H/D) ratio. It now uses the same building height for walls, roof panels, and gable ends on the same face of the structure. The height used is the ridge height for faces perpendicular to the ridge, and the mean roof height for faces parallel to the ridge. For flat roofs, it is the eave height.
This change is made for both NDS 2010 and NDS 2015 design setting selections.
In 2010, pressure coefficients CpCg for low-rise buildings were found in Commentary I-27 and Figure I-7 for MWFRS loads and in Commentary I-28 and Figure I-8 for C&C loads; in NBC 2015 they are in a new section, 4.1.7.6, and shown in Figure 4.1.7.6.-A, for MWFRS loads and Figure 4.1.7.6.-B for C&C loads.
There is no substantive difference in the generation of wind loads using these provisions, but the limitations on low-rise buildings given in Commentary I-26 vs 4.1.7.6.(1). NBC 2010 said that said that the coefficients are most appropriate for buildings with height/width (H/W) ratios less than 0.5, and must be used for H/W less than 1.0. NBC 4.1.7.6.(1) includes only the 1.0 H/W limitation,
The extensive use of "mid-roof height" in NDS 2015 leads us to believe that is what is intended as H in the H/W ratio. Therefore, the program no longer uses the height you select in the Design Settings to determine this, and always uses the mid-roof height.
This change is made for both NDS 2010 and NDS 2015 design setting selections.
For buildings with varying widths on each level, the program previously determined the width of the structure by taking the largest extent in each direction of any of the levels on the structure, then using lowest value of the NS and EW dimensions so determined. Thus, a structure with a large podium base and a narrow tower would use the base as the width of the structure.
To avoid this situation, the program now uses the average dimension of all levels on the structure in each direction, then the lesser of the two directions.
This change is made for both NDS 2010 and NDS 2015 design setting selections.
Warning messages shown when using the low buildings for H/W ratios between 0.5 and 1.0 have been removed. Those for 1.0 and greater have been modified to show NDS 2015 references.
In NBC 2010, pressure coefficients Cpi were found in Commentaries I-30 and I-31; in NBC 2015 they are in NBC 2015 4.1.7.7. The three categories for were previously called Category 1, Category 2, and Category 3, but now Table 4.1.7.7. has a column called Building Openings, with the associated Cpi values. The word "category" is no longer used.
The Site Dialog input in the Internal Pressure data group is renamed to Openings from Category.
The choices that were previously
Exceptionally sealed
Ord. closed openings
Large open openings
are now
Uniform, small, < 0.1% area
Non-uniform, resistant, closed
Large, often open
This change is also reflected in the Site Info echo in the output report.
In the Load Generation Details report, longer descriptions are given, as follows
Uniformly distributed, small, less than 0.1% of total surface area
Non-uniformly distributed; if significant, wind-resistant and closed
Large, likely to be open during storms