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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.
Shearwalls now offers the choice of using the 4-term deflection equation in CSA O86 11.7.1.2 and a 3-term linearization of this equation. The linearization follows a formulation in the AWC Special Design Provisions for Wind and Seismic, equation 4.2-1, for shearwall deflection analysis in the United States.
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.
The 3-term equation can be preferable because 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. Furthermore, using the 4-term equation, Irregularity Type 4 – In Plane Discontinuity (stiffness) from NBC 4.1.8.6 is detected for adjacent storeys even if they are constructed of identical materials (see ).
A Design Setting called Linearize deflection equation has been added to allow you to choose between these two methods It is recommended to choose Never, but switch to Always 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 the choices of Always and Never have been chosen to allow the future implementation of a hybrid design for which we allow 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 10, the switch must be made manually and for all shearlines in the structure.
Mixing the two methods in the same design could 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, so further research is needed before a hybrid approach is attempted.
The following terms in the two-term equation
are replaced by
The calculation of Ga for wind design uses the formula
For seismic design,
Conversion between SLS and ULS load factors is unnecessary, as they are all 1.0; only the ULS importance factor IE differs.
The unblocked factor Jub is applied only to the v value in the main deflection equation. not the vs and vw values in the calculation of Ga. Dividing v by Jub is equivalent to factoring the whole shear stiffness Ga by Cub.
CSA O86 has a further non-linearity to those in the main deflection equation in 11.7.1.2, the elongation for anchorages, which is
Analogous to the procedure for calculating Ga, this is
Using the linearized setting, the program is always able to equalize deflections for all segments on a wall, except those cases that there is not sufficient loading to allow the same deflection to be achieved in some segments as for other segments in the line that have a relatively high constant deflection due to factors such as gypsum wallboard nail slip. This happens only for lightly loaded shearlines.
Even when you choose not to linearize the equation for load distribution and storey drift, the linearized equation is used for the detection of Type 4 Vertical Discontinuities (stiffness) irregularities. Refer to for more d Using the linearized setting, the program is always able to equalize deflections for all segments on a wall, except those cases that there is not sufficient loading to allow the same deflection to be achieved in some segments as for other segments in the line that have a relatively high constant deflection due to factors such as gypsum wallboard nail slip. This happens only for lightly loaded shearlines.
etails.
If the Design Setting option to linearize deflections is chosen, the Deflection table shows only one deflection value called Shear defl, rather than separate shear and nail slip deflection. The Ga value is also shown, and the Vn and en values for nail slip show the values at shearwall capacity vs or vw used to calculate Ga
The legend at the bottom of the table has been modified to reflect these changes.
The database of hold-down connections has been updated to conform to the Canadian Limit States Design version of the Simpson Strong-Tie Wood Construction Connectors Catalogue, page 83, as of January 17th 2018. This is found at http://embed.widencdn.net/pdf/plus/ssttoolbox/oknkjgclgk/C-C-CAN2018.pdf.
For consistency with other cells containing phrases rather than numeric data, Shearwall relative rigidity and Design shearwall force/length are now in sentence case rather than title case.
The aspect ratio (shearwall height / length) of each shearwall segment is now shown in a column in the table next to the full height sheathing. It is defined in the table legend.
Occasionally, walls would appear out of order in the table. This has been corrected.
The dashes that appear for fields that do not contain data are now center-justified. (QA Item 24a)
The table header Grade/Ply has been changed to Mark/Ply, as the OSB Table 9.3C with grades no longer exists. The legend item below has also been changed
In the Mark/Ply (formerly Grade/Ply) legend item (QA Items 75a and 75b)
Refers to plywood plies and OSB panel mark, not just "mark" and "plies".
"see" note 8 is not "shown in" note 8
The words panel marking have been changed to panel mark in the note below the table.
The list of notes without numbers has been differentiated from those with numbers, with the former headed by General Notes: and the latter by Material-specific Notes.
The note about compliance with O86 11.8.8 which disallows gypsum contribution for 5- and 6-storey structures was mistakenly replaced with one about Rd and Ro values. This has been corrected.
When C&C nail withdrawal design failed for non-shearwalls, the Design Summary said under capacity walls were found but did not list them. This has been corrected.
The words CSA O86 have been added to the reference 11.8.3.2 about overcapacity ratio under the seismic information, as most seismic provisions are from NBC, and there are no nearby references to O86.
Shearwalls were not always listed in order as they occur from west to east or south to north. This has been corrected.
The table legend has been improved to
Hold-downs were not always listed in order as they occur from west to east or south to north. This has been corrected.
The word wind has been removed from wind direction in the table, as it was appearing for seismic design as well as wind.
Drag struts were not always listed in order as they occur from west to east or south to north. This has been corrected.
The word O86 has been placed before
The hold-down elongation values and possibly other values in the table were not always being rounded to the nearest 1/10 of a millimeter, but rounded to the 1/10 value in the other direction. This has been corrected.
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 0.5%, which ensures that when deflections are not equalized to that level, it is apparent in the output table.
The C&C load for nail withdrawal design was the highest of all storeys on a shearline rather than the load on the level of the wall being designed. This has been corrected.
In wall input view, the program did not allow input of nail diameter for the interior side of a wall. For power driven nails with multiple possible diameters, this meant that the program selected a diameter at random for design. For all other nails, selection of nail length uniquely determines the diameter so there was no problem.
It is now possible to select nail diameters for both sides of the wall.
The 1.2 drag strut factor from CSA O86 11.8.6 was being applied regardless of the value of IEFaSa (0.2) when according to 11.8.1 Drag struts = 1.2 (11.8.6) in the Elevation view legend always appeared regardless of whether this factor was applied. It now only appears for high seismic zones when the 1.2 factor also appears for the "S" component of hold-down forces.
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 power driven nails are selected with unknown as the diameter, the program wasn’t determining the worst case of seismic, wind, rigid and flexible design for the nail diameters so that extra wall groups corresponding to the nails designed for each of these criteria were generated, and appeared throughout the design results. This has been corrected.