THE NATURE OF THE VERTICAL DISTRIBUTION OF SEISMIC RESPONSES IN MULTI-STORY BUILDINGS

This study investigates the vertical distribution of seismic response of four common types of seismic force resisting systems (SFRSs): special reinforced concrete shear wall, steel special moment frame, steel special concentrically braced frame, and steel buckling-restrained braced frame. Current design codes incorporate the effects of inelastic behavior via a response modification factor that reduces the elastic demands, and SFRSs are designed for essentially the same vertical distribution of seismic loads. However, because of different inelastic deformation mechanisms, a particular SFRS may experience a different vertical seismic force distribution than another. Due to the significance of the vertical force distribution for the design and detailing of structures, force distribution patterns have been studied by researchers, but an extensive comparison of the four SFRSs designed to accommodate the same seismicity has not been conducted. For this reason, all buildings are designed for a generic site in this study. A series of Nonlinear Time History Analysis (NTHA) of 4, 8, 12, 16, and 20-story buildings are carried out using a suite of sixteen code design spectrum compliant ground motions at DBE and MCE intensity levels. High-performance computing resources are exploited by running simulations as parallel jobs. Seismic response is examined using floor forces, story shears, story moments, and inter-story drift ratios. NTHA results demonstrate significant differences between NTHA results and design forces. The force distribution patterns are found to be affected by the number of stories, inelastic deformation mechanism, and concentration of inter-story drifts. Results indicate that buildings with different SFRS exhibit considerably different vertical distribution of forces and large amplification of forces, which suggest that a particular design force pattern for a particular type of SFRS, as well as larger diaphragm and shear design forces should be considered in the design procedure.