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Structural Iteration for Irregularities
For seismic design, the program went through two iterations of designing the entire structure as follows.
Iteration 1
The program designed using the user-input method of designing for hold-downs and drag struts.
Iteration 2
The program determines irregularities on the structure, and if Applied Force had been used as the method of determining hold-down and drag strut forces, the program program redesigns the entire structure, determining hold-down and drag strut forces for the shearlines affected by irregularities by shearwall capacity, to comply with NBC 4.1.8.15-6 where applicable.
Rigid Distribution
Rigidity based on Shearwall Capacity
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.
Equal Rigidity or Manual Rigidity Entry
For these distribution methods, the rigidity is independent of shearwall design, so no iterations were necessary.
Distribution within a line
Before the introduction of deflection analysis, if you selected not to allow dissimilar materials on the line, it was possible to determine load distribution within a line based on relative capacities and identify the critical wall for design ahead of time and an extra design iteration was not needed.
If dissimilar materials are allowed, the program must design each wall separately so that the design could result in a redistribution of loads, and a iterations were peformed to design the wall and redistribute loads until a there was no difference in walls designed.
Hold-down vs Anchorage Loop
If the user chooses to allow anchorages, the program does several iterations of design based upon trying to counteract a failed design by increasing the Jub factor. On the first loop it places the hold-downs only where they are required by CSA O86. Then it places them at the ends of the shearline, then at the ends of all walls, then at the ends of all segments.
This acts in concert with the Design Setting that indicates whether hold-downs should be at those locations, and the setting that allows you to over-ride these locations to achieve design.