Determination of response modification factor, R, for gate bracing system using Incremental Dynamic Analysis method (IDA)

Gate bracing system is a form of concentric bracing systems which is similar to chevron (inverted V) bracing. To provide enough space for openings، the members are not direct and joined together with different slope in one point. Bracing is joined to connection joint of beam and column in its other end. In this paper، overstrength factor، ductility factor and response modification factor of steel frames with gate bracing are evaluated. To do it، buildings with different story numbers on soil type II are considered. Static push over analysis، linear dynamic analysis and nonlinear incremental dynamic analysis are performed using Opensees software. To consider the uncertainties associated with earthquakes and to perform Incremental dynamic analysis procedure، 10 records of sever earthquakes ever happened including records of Bam and Tabas earthquakes are selected. Finally ductility factor، overstrength factor and response modification factor for gate bracing system are calculated and values of 3. 5 and 5 has been suggested for ultimate limit state and allowable stress design method.