Evaluation of Response Modification Factor and Seismic Behaviour of Dual Systems of RC and Steel Structures Using Adaptive Pushover Analysis (APA)

Non-linear dynamic analysis is considered the most complete method for estimating seismic performance parameters of a structure. However, due to its complexity and time consumption, researchers and seismic code authorities suggest the use of non-linear static analysis (also called Pushover Analysis). With the development of the application of Pushover Analysis in recent years, more advanced types of Pushover analyses are proposed, attempting to take into account different important behavioral features of the structures during an earthquake, such as the effect of higher modes and/or the effect of changes in modal characteristics of the buildings during seismic excitations. Adaptive Pushover Analysis (APA) is one of these proposed methods in which the structural stiffness and the lateral load pattern change during a given step of the loading. Earthquake forces are usually a few times more than the value obtained from seismic codes. This decrease is enforced by response modification factor. In this paper, effective parameters in seismic design of dual structural systems have been explained by using the capacity curve obtained from Adaptive Pushover Analysis. Using Adaptive Pushover Analysis, seismic performance parameters such as response modification factor, over-strength factor and ductility ratio are evaluated for two different types of dual-structural systems: 1) RC moment resisting frames (MRFs) with steel braced frames, and 2) steel (MRFs) with RC shear walls. These two dual-structural systems have 5, 10 and 15 stories and are designed according to IRAN's seismic code (Std. No. 2800, Third Edition). For Adaptive Pushover Analysis, 22 far-field earthquake records recommended by FEMA-P695 are used. Mean value of response modification factors for different dual systems is obtained to be 7.22. Dual systems of RC MRFs with steel braced frames showed better seismic performance and are therefore highly recom-mended for rehabilitation of existing RC structures. According to the results obtained, the building height has significant impact on the response modification factor.