09-04-2013, 08:42 AM
METHOD OF MODAL COMBINATIONS FOR PUSHOVER ANALYSIS OF BUILDINGS
Author: Erol KALKAN and Sashi K. KUNNATH | Size: 0.37 MB | Format: PDF | Quality: Unspecified | Publisher: 13th World Conference on Earthquake Engineering Vancouver, B.C., Canada | Year: 2004 | pages: 15
Nonlinear static procedures (NSP) are finding widespread use in performance based seismic design since
it provides practitioners a relatively simple approach to estimate inelastic structural response measures.
However, conventional NSPs using lateral load patterns recommended in FEMA-356 do not adequately
represent the effects of varying dynamic characteristics during the inelastic response or the influence of
higher modes. To overcome these drawbacks, some improved procedures have recently been proposed by
several researchers. A method of modal combinations (MMC) that implicitly accounts for higher mode
effects is investigated in this paper. MMC is based on invariant force distributions formed from the
factored combination of independent modal contributions. The validity of the procedure is validated by
comparing response quantities such as inter-story drift and member ductility demands using other
pushover methods and also the results of nonlinear time history analyses. The validation studies are based
on evaluation of three existing steel moment frame buildings: two of these structures were instrumented
during the Northridge earthquake thereby providing realistic support motions for the time-history
predictions. Findings from the investigation indicate that the method of modal combinations provides a
basis for estimating the potential contributions of higher modes when determining inter-story drift
demands and local component demands in multistory frame buildings subjected to seismic loads.
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