huangyhg

scaling of dynamic base shears
below are my assumptions for doing a response spectrum analysis and design. any comments would be appreciated.
1) perform modal analysis per section 12.9 of asce 7-05.
response spectral ordinates sa as defined in 11.4.5 are scaled by dividing them by (r/i).
2) cqc method is used for combining modal response parameters.
3) compare the dynamic base shear (vt) with the static base shear (v) obtained from equivalent lateral force procedure.
4) if vt < 0.85 v, scale the design forces by a factor 0.85*v/vt, which basically scales up the dynamic base shear to 0.85v.
5) if vt > v, no further scaling is required.
note that asce 7-98, required the dynamic base shears to be scaled to 1.0 v. i have not seen this requirement any more in asce 7-02 & asce 7-05.
don't forget to include the gravitational acceleration constant (g) in your scale factor.

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