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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.
The way that force is distributed with a line depends on the Design Settings Shearwall Rigidity per Unit Length and Distribute Forces to Wall Segments based on Rigidity.
This setting must be checked to allow the Shearwall Rigidity per Unit Length choices to affect the distribution within the line. If it is not checked, the same shearwall force per unit length is applied to the entire shearline. Deflections in general will be different for each segment along the line, and the largest deflection is taken to be the one used for storey drift calculations.
This rigidity is used for both the distribution of applied loads to the shearlines using the rigid diaphragm method, and for distribution within a line if the Distribute Forces to Wall Segments based on Rigidity box is checked.
A new method has been added to the previous three selections – Use shearwall deflection to calculate rigidity. If any of the three methods that were in previous versions of the program are selected, then deflections in general will be different for each segment along the line, and the largest deflection is taken to be the one used for storey drift calculations.
If both the Distribute Forces to Wall Segments based on Rigidity box is checked, and the new Use shearwall deflection to calculate rigidity button is selected, then the program will attempt through an iterative procedure to equalise deflections on the shearline, by redistributing the shear force v to the segments until the deflections calculated with Eqn. C4.3.2-1 are the same.
This is the recommended procedure, as it is mandated by SDPWS 4.3.3.4 as a condition for summing the capacity of walls along a line.
Because deflection is highly dependent on aspect ratio of the segments, and the hold-down forces and hold-down devices employed at each segment, deflection can be highly variable along a line, so that some segments draw negligible force. Furthermore, some segments have constant components to deflection ( non-wood-panel nail slip, hold-down overrides, extra hold-down components) that yield a deflection with minimal loading that is higher than the deflection on other segments even if all the shearline load was applied to that segment.
If these situations occur, the program assigns zero load to those segments that are drawing negligible loads ( less then .1 lb), and equalises the deflection on the remaining segments. The segment that gets zero force is treated as an opening or a non-shearwall for the purpose of final hold-down and drag strut calculations. This segment has no effect on shearwall design: since all shearwalls must be composed of the same materials (SDPWS 4.3.3.4), the program finds the most heavily loaded segment for shearwall design.
The mathematical system used to model shearwall deflections along a line is not necessarily determinate. On occasion, the routine is unable to equalise deflections along a line, oscillating between solutions that do not equalise deflections. In this case, the deflections that arise from the last iteration before a limit is reached are used.