ANALYTICAL STUDY OF THE MAXIMUM ROTATIONAL DUCTILITY OF BEAMS IN STEEL MOMENT RESISTANT FRAMES CONSIDERING HIGHER MODE EFFECTS

Information regarding the nonlinear dynamic response of steel moment resistant structures aected by earthquake should be as complete and integrative as possible to insure the fulllment of pre-determined limitations in design. Meanwhile it should be simple enough for implementation by professional engineers. To this end, the main objective of this study is to increase awareness of the nonlinear dynamic response of steel moment resistant frames (SMRF) and to provide methods for measuring the maximum load seismic demands of these structures using maximum global (roof) and interstory (intermediate) demands (which can be estimated by SDOF system demands). A further objective of this study is to provide a relation between interstory drift and the maximum local demand of beams. To this end, a considerable number of SMRF, short, mid and high rise structures, with a dierent number of stories and bays, were modelled in DRAIN2DX and analysed using nonlinear time history (NTHA) and conventional pushover analyses (CPO). The results of studies showed that beam ductility values are signicantly higher than interstory and global ductility. Furthermore, higher mode eects on the increase of rotational ductility in the upper stories of high-rise buildings are completely sensible. This was seen on the distribution of force and deformation demands in CPO and NTHA analysis states. It is possible to calculate maximum beam ductility, in respect to target ductility, the number of bays and the foundamental period of frame, with acceptable precision, by the proposed equation of the models in this study.