M. Ghassemieh, R. Kargarmoakhar, University of Tehran, Tehran, Iran
Traditional philosophies behind different methods of designing structures against natural hazards such as earthquakes have changed in recent years. Failure of many structures designed by the conventional methods during recent earthquakes, the improvements in the analyses methods, and the more complicated performance demands by the building industry has led to more effective methods in structural design. Many seismic codes have been introduced to make designing procedure more easily which permit a reduction in design loads, taking advantage of the fact that the structures possess significant reserve strength and capacity to dissipate energy which are incorporated in structural design through response modification factor. The factor represents the ratio of the forces that would develop under the specified ground motion if the structure were to behave elastically to the prescribed design forces at the strength limit state. Shape memory alloys (SMAs) with unique superelastic properties have many interesting characteristics which can be utilized in structures. SMAs are materials capable of undergoing large recoverable strains of the order of 10% without exhibiting plasticity. High damping capacity, recentering, high fatigue resistance, no need of maintenance and durability are among the characteristics which have made SMAs an effective damping device. In this study, Enhanced SMA braced frames are designed through designing BRBFs, in that the model used for SMA has the same behavior in tension and compression similar to BRBFs hysteretic curves. This leads to simplify the design process. Buckling restrained braces are replaced with SMA braces with the same strength and stiffness to obtain different parts of the response modification factor. Static pushover analysis, nonlinear incremental dynamic analysis and linear dynamic analysis have been performed using Seismo Struct software of model structures with various stories and span lengths. The result suggests higher response modification factor for structure utilizing SMA than its steel counterpart.
Summary: Finding a simple way for predicting the structures behavior under seismic loads by introducing response modification factor using recommended procedures in international codes for structures whose properties have been improved with SMA.
