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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.
For seismic design, the program went through two iterations of designing the entire structure as follows.
The program sets the redundancy factor r to 1.3, and designs shearwalls based on the shearline forces factored by r.
The program recalculates r based on the distribution of shear resisting elements designed in the first iteration. If it turns out to be 1.0, it refactors the shearline forces and redesigns the shearwalls based on the new forces.
The program then calculates r based on the final distribution and outputs it in the Design Results, in the Storey table. It was therefore possible to have a different r shown in the design results than was used to calculate the shearwalls. Furthermore, because this final r would be 1.3, the shearwalls could be under designed for the actual forces that would be created with the new r value.
In practice, this occurred very rarely.
The program designed walls for flexible diaphragm design, and then used the rigidities based on the capacity of those walls for rigid diaphragm shearwall design. .
It did not go back and recalculate rigidities for the new walls designed for rigid design, and continued to show the flexible-designed shearwall rigidities as the rigidities of the rigid-designed walls.
For these distribution methods, the rigidity is independent of shearwall design, so no iterations were necessary.
Before the introduction of deflection analysis, it was possible to determine load distribution within a line based on relative capacities ahead of time, because the only things affecting it is the perforation factor and the seismic height-to-width factor (walls within a line cannot have different materials.)
The program therefore identified the critical wall for design ahead of time and an extra design iteration was not needed.