Seismic Analyses Questions
Seismic Analyses Questions
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Seismic Analyses Questions
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RE: Seismic Analyses Questions
These are some pretty general questions. Please consider my answers partial at best.
1) We don't. Static (ELF) and dynamic procedures are two different animals.
2) See #1. Two different paths.
3) Diaphragms distribute seismic loads originating mostly in the floor and roof decks to the vertical lateral force resisting elements (walls, braces, etc.)
4) Generally wood and untopped steel deck diaphragms are flexible while concrete, concrete topped, and discretely braced diaphragms are not. ASCE 7-10 provide guidance.
5) Displacement is usually conceived of as an absolute value; drift is usually evaluated on story by story basis h/xxx.
6) We multiply by R to try to convert an elastic displacement to displacement that includes the effects of post yield displacement.
7) It depends on your local code and the dynamic procedure that you choose. Usually people do employ load cases including eccentricity in dynamic procedures.
8) It is considered improbable that design EQ and design Wind loads will occur simultaneously.
9) Neither. Mode shapes with periods close to the period of the excitation function attract displacements which generate strains and forces.
10) Try this: Link
11) If the members are part of the lateral load resisting system, seismic influences the design significantly. If not, the members need to be able to accommodate the expected seismic drift.
12) See #11.
13) This is too broad a question for me to be able to provide a meaningful answer. Check all members for their capacity to resit load effects including seismic. Follow detailing recommendation in your local code to ensure ductile response where you need it. Check drift limits.
14) Not normally.
15) Damping depends on a number of things, predominately the materials involved in construction. I believe that ELF procedure response spectra are based on 5% critical damping.
16) See #5
17) Generally one. Engineers will often vary parameters in an attempt to bracket behavior.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Seismic Analyses Questions
This appears to be simply a "floor" to the dynamic design to ensure that someone doesn't mis-use or mis-analyze a structure using flawed parameters or assumptions.
See ASCE 7-05 or 7-10 section 12.9.4.
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RE: Seismic Analyses Questions
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.