The Effects of Higher Modes on the Response Modification Factor of Tall RC Buildings

The current seismic design procedures in the codes are typically based on the linear analysis and the first vibration mode. There are no specific recommendations to consider the effects of the higher modes contribution on the seismic behavior of tall buildings. Thus, by designing these structures and using the proposed codes behavior factor, the result of nonlinear analysis might be different. The purpose of this study is to consider the effects of higher modes on the strength reduction factor. In this regard, five special RC shear wall moment-resisting frame structures with 5, 12, 18, 30 and 50 stories were designed and modeled by PERFORM3D software. In order to consider the influence of higher modes, a single-run story shear-based adaptive pushover (SSAP) was selected to achieve capacity curve. The empirical strength reduction factor of each frame was calculated based on the capacity curve. In addition,the strength reduction factor of the frames obtained from nonlinear dynamic analysis and compared to those of SSAP and the code one. It was conclude that the R value recommended by codes is incompatible for tall buildings and it should be modified for tall structures.