EFFECT OF BIDIRECT IOANAL NEAR FIELD GROUND MOTIONS ON INELASTIC RESPONSE OF 3D MODELED R.C FRAME BUILDINGS

Investigations confirm that near field ground motions differ from far field ground motions. A vast number of studies in the near field area have been conducted on 2-dimensional simiulations of structures, and no comprehensive studies have been conducted on 3-Dimensional nonlinear models of structures subjected to near field ground motion. Since a 2-dimensional analysis might cause some error due to the approximation and presumptions in mass, stiffness and also not taking into account the P-M2-M3 interaction of forces and deformations, the need for a 3-D analysis can be sensed. The main objective of this study is to investigate the effect of near-fault ground motions with forward directivity on the seismic behavior and inelastic response of 3D concrete frame buildings with various fundamental periods and also determinin whether different faulting mechanisms result in different seismic demands on structures. In addition, investigating whether or not the demands obtained from 2D and 3D analyses conducted on 3D models are in agreement or not, in order to understand the importance of 3D analyses on buildings. The buildings are subjected to far field ground motions as well, and responses of the two cases will be compared to form a better notion of the difference between a structure’s behavior under near and far field ground motionsNoticeable difference is observed between strike slip, dip slip and farfield records, both in peak inter story drift patterns, values and the story that experiences the maximum peak inter story drift. As it is expected, the studied buildings show higher inters-story drift demand in comparison with those reported from 2D analyses conducted on 3D models in this study. This would be due to the fact that the P-M2-M3 interaction effects on derived responses are more significant from those of 2D analyses and ofcourse 2Dmodels. The conclusion inferred from current study emphasizes the need to use 3D models instead of 2D, where the influence of near field record is investigated.

کلیدواژه ها:

Near-fault ground moti ons ، Forward Directivity ، Bidirectional Nonlinear Time History Analysis ، 3-Dimensional