Evaluation of Steel Moment-Resisting Frames Performance in Tall Buildings in Near Fault Areas

Evaluation of strong ground motions and effect of them on performance of structures are the important subjects that nowadays are considered in structural and earthquake engineering. It is necessary to evaluate of the near-field earthquake characteristics and effect of them on response of buildings. In this paper, the performance of steel Moment-Resisting Frames (MRFs) in tall buildings in near fault areas has been studied. Six steel MRFs 15- and 20-story with three different ductility; ordinary, intermediate and special moment-resisting frames have been designed according to the Iranian seismic code 2800 (3th Edition) and Iranian national building code-steel structures (Part 10). To assign the performance parameters of frames and to present the effects of near-field earthquakes on steel MRFs, pushover and non-linear dynamic time history analyses have been performed and conducted for chosen structural models. The ensemble of used earthquakes contains both far-field and near-field earthquake records. It is worth mentioning that the selected earthquake records contain some strong ground motions from the 1978 Tabas, 1979 Imperial Valley, 1992 Landers and 1994 Northridge Earthquakes. According to the analytical results, concerning near-field earthquake records which emerge velocity pulses in their time history, the maximum values of story displacement, story drift, roof displacement and base shear are relatively higher than those which are obtained from near-field records that do not display velocity pulse and also those ones obtained from far-field strong ground motions. Based on using near-field earthquake records specially those ones that display velocity pulses, the calculated members stress and deformation resultants are higher than those ones that are recommended by the Iranian Seismic Code. Also, by more ductility in steel special moment-resisting frames the structural damping in non-linear domains can be considerably higher than the value of this parameter in other structural systems. This subject should be confirmed by comparing the calculated values of seismic base shear in analyzed models. On the other hand, in special moment-resisting frames, under the effect of near-field earthquake records which emerge velocity pulses, the maximum values of storey displacement and storey drift is much higher than allowable values which are recommended by the Iranian seismic code. Hence, it is advised to increase the capacity of member sections and connections, in order to achieve the code-defined limited values of displacement and drift demands in steel special moment-resisting frames.