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Generating Seismic loads

Generating Seismic loads

Generating Seismic loads

Can somebody help me understand the difference betweent the Equivalent lateral force procedure / Response history procedur / modal response spectrum procedure to generate the seismic loads and when it is recommended to use each method ?

RE: Generating Seismic loads

My understanding is the ELF is a simplification of a dynamic analysis for a 'typical' building. Usually defined as having 90% of the building mass participate in the first mode. If for one reason or another (mass irregularity, geometric irregularity, etc) you have less than 90% of your mass participating in the first mode, you need to do a modal response spectrum analysis and properly combine the effects of several modes to accurately capture your structures dynamic response.

Time history analysis is usually done on a case by case basis when you have site specific seismic information as a way of hopefully achieving reduced seismic forces as opposed to the traditional prescriptive methods of Ch12 in ASCE 7-10.

RE: Generating Seismic loads

Many thanks for your help, really appreciated.

RE: Generating Seismic loads

Section 17.4 in ASCE 7-10 provides instruction on when each of the analysis methods are permitted
and / or required.

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