Evaluation of behaviour factors of steel moment-resisting frames using standard pushover method

The structural performance limit (SPL) is an important parameter in the qualification of the behaviour factor (BF), because this factor is involved in the selection failure mode of the structure. EC8 does not indicate accurately criteria for define the failure mode or quantitative definition of the ultimate limit state corresponding to which values of BF frames are recommended. Moreover, the evaluation of the seismic strength of structures of buildings is usually carried out by the capacity design approach taking into account the nonlinear response of structure through the BF and in seismic design codes actual seismic load is reduced by this factor that takes into account several parameters including the capacity to dissipate energy, reserve strength and redundancy. Thus, the need for identifying BF in relation to its importance in the seismic design of frames seems indispensable. In this study, results of standard nonlinear static pushover analysis (NSPA) using SAP2000 program for steel moment-resisting frames (SMRFs) of different stories and bays were analyzed and compared and conclusions regard the effect of the structural performance limits and the capacity factor and other parameters on BF and its components are presented. It is found that the height and the capacity factor of frame have a profound effect on the BF and the value of this factor recommended by the EC8 is underestimated, mostly for low-rise frames.