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Re: Dynamic Analysis

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For your Dynamic analysis it should not make any difference whether you scale the actual response spectrum or the final resulting loads.  In fact, I believe that this what is normally done with most of the current analysis software such as RISA.  Where you need to be careful is when you get to ASCE 7-05 Section 12.9.4 for the scaling factor to insure you are comparing apples to applies.  That is, for V and Vt they both need to include or not include R and when calculating your scale factor.

Thomas Hunt

02/04/2009 06:24 PM
Please respond to seaint
Dynamic Analysis

We are working on a project in Southern California. According to ASCE7-05, we have to use the “Modal Response Spectrum Analysis” and use a Dynamic analysis for the lateral design.
The building has a combination of Steel and Concrete Special Moment Frames (steel on top and concrete at the bottom).
When we calculate the lateral forces based on Equivalent Lateral Force Procedure, the total lateral load is approximately 250 Kips.
When we run the Dynamic analysis, the lateral load is approximately 1200 Kips.
Section 12.9.2, of ASCE7-05, comments on dividing certain loads by R/I.
In your opinion, could we divide the lateral load obtained from Dynamic analysis by R/I, which is the same as dividing the Design Spectrum by R/I?

Thank you,

Farzin S. Rahbar, SE
David C. Weiss Structural Engineer & Associates, Inc.
(818) 227-8040 Ex. 13 Fax: (818) 227-8041

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