Effect of rigid content on modal response combination

Abstract

The effects of rigid content of response on modal response combination are studied. The rigid response coefficients are calculated for 40 earthquakes and four damping ratios. The modal response is evaluated for a range of frequencies from damped periodic to rigid. The presence of rigid content in the modal responses having frequency less than rigid frequency is investigated. The related key frequencies and rigid frequency are studied. It is found that the rigid content of the response and the related key frequencies are functions of the damping ratio and found to be different from those proposed in the earlier studies. New simplified formulations are proposed for determining the rigid response coefficient for the combination of modal responses.