چكيده به لاتين
Structures that are located in seismically active regions often may be subjected to ground motions containing the seismic sequence. Seismic sequence phenomenon is the occurrence of successive earthquakes with significant PGA in a short time after the first vibration. Studies about different responses of the structure under seismic sequence phenomena, such as damage, ductility, displacement, behavior factor, all indicate that the effects of successive earthquakes, depending on their severity, have significant impacts on the different demands of structures. For instance, the behavior factor (R factor) is one of the significant parameters in the study of structural response that decreases the lateral forces of the earthquakes. Therefore, the structure with non-elastic deformations absorbs a great amount of quake energy, thus the earthquake energy decreases considerably. In this study, three moderate steel moment frames and three special concentrically braced frames (chevron-braced frames) with 3, 7, and 11 stories that respectively represent short, medium, and high-rise structures are designed in SAP2000 software according to Iranian seismic codes (standard no. 2800) and are modeled in OpenSEES software. After the design of the samples, individual and sequential critical seismic scenarios with/without successive shocks, are selected and the R factors of steel moment frames are calculated from the results of Incremental Dynamic Analysis (IDA(, time history and nonlinear static analysis (pushover). Finally, the R factors of the structures are obtained from the results of the aforementioned analysis and are compared under single and successive earthquake records. The results show that the structural collapse capacity decreases due to stiffness and strength deterioration caused by the first seismic shock and thus, the level of damage increases. As a result, in all steel moment frames and braced frames, the average of the R factors show reduction rate under successive earthquakes comparing to the individual one.
