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Change in modal story shear

Alex Piket — Fri, 21 May 2021 04:05:58 GMT

Hi:

When designing diaphragms for a project, and using ELF, I typically review the change in story shears (in RAM Frame) and multiply the values by the appropriate overstrength factors, where it's needed. For the same project, and after running a modal analysis, there appears to be a significant shear reversal resulting in large change in story shear values, in one of the stories. Which procedure is more appropriate for the design of diaphragms? Consider sign for analysis results is checked under options.

Thank you.

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Wed, 13 Mar 2019 04:35:26 GMT

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Cs(max) ASCE 7-16

Alex Piket — Wed, 13 Mar 2019 14:05:07 GMT

The upper value of 'Cs' computed in accordance with eq. 12.8-2 need not exceed eq. 12.8-3 or 12.8-4, whichever applies. In Frame, under 'Loads and Applied Forces', this check doesn't appear to be included. What am I missing?