A response spectrum method to estimate peak floor acceleration demands of multistory buildings subjected to earthquakes and responding elastically is presented. Available response spectrum methods and modal combination rules such as SRSS or CQC have been used for estimation of relative displacement and inter-story drift demands but cannot be directly used for estimation of peak absolute (total) floor acceleration. The proposed response spectrum method not only considers the correlation between modal accelerations, but also takes into account the correlation between ground acceleration and modal accelerations. The formulation for estimation of peak floor acceleration is presented. Closed form solutions for correlations between the modal accelerations as well as modal accelerations and ground accelerations have been derived for filtered white noise inputs. Empirical equations for correlations are presented. To verify the results, a continuum model of building consisting of a shear beam connected laterally to a flexural beam previously studied by the authors has been used and combined with the presented closed form and empirical formulations for the purpose of parametric analysis. It is shown that results of the proposed response spectrum method match with the time history analysis with great accuracy.
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