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Story drifts from STAAD with dynamic analysis

Story drifts from STAAD with dynamic analysis

Story drifts from STAAD with dynamic analysis

(OP)
How do you obtain story drifts from STAAD with a dynamic analysis? Should you use the node displacements? Or the PRINT STORY DRIFT command? And do you need to factor up displacements Cd/I (see ASCE 7-05 12.9.2)

Thanks

RE: Story drifts from STAAD with dynamic analysis

I'm not totally familiar with the STAAD output, but I usually find it's easier to look at the individual story drift rather than look at global drifts. In fact, I often use a drift ratio based on the allowable drift. If you are comparing your story drift to the allowable from Chapter 12, then yes you need to increase the elastic story drifts by the factor you mention. I find it much easier to just look at a drift ratio and not worry about increasing the elastic drifts.

RE: Story drifts from STAAD with dynamic analysis

(OP)
Thanks, you mention elastic drifts but this is for a dynamic (or modal) analysis

RE: Story drifts from STAAD with dynamic analysis

The section you reference directly states, "The values for displacement and drift quantities shall be multiplied by the quantity Cd/I." Unless you are using a nonlinear analysis, the drifts you're getting are elastic, so you increase them based on the plastic response of the SFR system.

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