Peak floor acceleration demand prediction based on response spectrum analysis of various sophistication

Abstract

This paper addresses the prediction of the median peak floor total acceleration (PFA) demand in spatial elastic structures subjected to seismic excitation. The prediction is based on various response spectrum methods of different degrees of sophistication. Beginning with a recently presented complete-quadraticcombination (CQC) rule for PFA demands, several approximations and simplifications concerning the correlation between modal contributions, peak factors, and cross-spectral moments are discussed, leading to the proposed modified modal combination rules. On several earthquake-excited multi-story spatial generic frame structures, the accuracy of the considered rules is assessed. The outcomes of response history analysis serves as benchmark solution. The results show that the modified CQC rules are simple in practical application and lead to reliable estimations of the median PFA demand of spatial structures with negligible loss of accuracy if peak factors are considered.

Simplified Prediction of Peak Floor Accelerations in Inelastic Wall Structures

“…Therefore, the peak factor, which represents the ratio between the peak acceleration and the mean square acceleration of a normal stationary random process [5,6], is unity, i.e. p i = 1.…”

“…Preliminary studies have shown that this relation can also be applied for structures with moderate hardening backbone curve. The modal peak factors of the higher (elastic) modes, p i , i > 1, and the peak factor of the response process, p r , can be estimated by the framework for elastic structures provided in [5,6], as preliminary studies have shown.…”

“…However, a multi-modal SRSS approximation of the median PFA demand yields for the the upper floors reasonable predictions of this response quantity, because the effect of the PGA diminishes with increasing height, see the dashed graphs in the third row of Figure 10. It should be noted here that the SRSS modal combination rule is deemed to fail for estimating PFA demands in spatial structures, because closely spaced modes are neglected [5,6]. …”

“…The approach combines pushover analysis for predicting the structural strength ratio, and subsequent application of a modified response spectrum method that yields the median PFA demand of the considered structural system [5,6]. For reasons of simplicity, this novel approach is elaborated for structural walls, where in general the inelastic deformations are confined to the base.…”

“…The contribution of the first mode inelastic median PFA demand is subsequently superposed with the elastic PFA demands related to the higher modes, using a modified complete-quadraticcombination (CQC) modal superposition rule, originally derived for unlimited elastic structural behavior [5,6].…”