Seismic Response by SRSS for Nonproportional Damping

A method is presented to obtain seismic design response of linearly behaving structures with nonproportional damping characteristics. For such systems, time history analyses are usually performed to obtain accurate seismic response. To obtain design response, such procedures can become expensive and cumbersome as an ensemble of time histories may have to be considered as seismic input. Other procedures have been developed to ascertain appropriate values of modal dampings so that modal analysis approach and thus commonly adopted square-root-of-the-sum-of-the-sqaures (SRSS) procedures can be used. The approach presented here considers nonproportional damping effects exactly in analytical sense. It uses state-vector formulation and is based on random virbration priciples. The approach is similar to conventional SRSS approach and thus ground response spectrum can be directly used to obtain designd respose.