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Design Settings
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.
Shearwall Rigidity per Unit Length
In the data group called Shearwall Rigidity per Unit Length, (previously known as Rigid Diaphragm Analysis), 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, as distribution within the line is based on shearwall capacity. The largest deflection is taken to be the one used for storey drift calculations.
Distribute Forces to Wall Segments based on Rigidity
This setting has been added to allow you to distribute forces based on the Use shearwall deflection to calculate rigidity choice to each wall within the shearline based on rigidity. If checked, the program will attempt to equalise deflections along the shearline. If it is not checked, distribution within the line is based on shearwall capacity, and 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.
Equalisation of Deflection
If both the new 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 9.7.1.11 are the same.
Zero Force
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 than 1 N), 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..
Non-convergence
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.