Seismic Behavior Analysis Of Regular RC Frames Subjected To Multi-Dimentional Near-Fault Ground Motions

According to present codes, the vertical ground motion is not considered in the low and medium intensity regions, however, the ratio of the vertical to the horizontal component of the ground action in high intensity region is 0.65 in recent earthquake events. In present study, based on the regular RC frame structures, four representative multi-store reinforced concrete frames are designed. By using the finite element software SAP2000, the three dimentional frame models are built, and the elasto-plasticity time history analysis is used to analyse the seismic response under combined effects of horizontal and vertical ground motions, compared with those under horizontal ground motions only, In this paper, the displacement, the internal force, the bearing capacity and the distribution of plastic hinges of the frames considering vertical ground motion are evaluated, the failure mode and seismic performance considering vertical ground motion are analysed. The conclusions of this paper are as following:(1) In general, for the seismic displacement of the frames of all intensity regions, the vertical ground motion has no significant effects on the topmost displacement, the inter-story displacement rotation and story displacement.(2) The axial loads of the columns varies significantly considering the action of vertical ground motion subjected to the high earthquake. Comparing with inputting horizontal ground motion only, the peak value of the axial loads of exterior column increased more obviously when inputting horizontal and vertical ground motion than the interior column.(3) For the frame in the intensity 7(0.1g) region, the vertical ground motion produce evident variation of the axial load, but the influences on seismic performance of the frame is not that significant than that of high intensity regions. Though there is some tendency of tension force, actually the force does not appear. According to new seismic code, the bending capacity of the column in intensity 7 region frame is further strengthened, the bearing capacity of the column is well guaranteed. For the frame in intensity 9(0.4g) regions, the bending capacity of the column is calculated using the real longitudinal and lateral reinforcement ratio of the beam, so the bearing capacity has a reliable guarantee and the combined horizontal and vertical ground motion did not change the developing and distribution of the column-hinge of the frame. Considering the combined horizontal and vertical ground motion do not produce adverse effect on yielding mechanism and failure mode to intensity 7(0.1g) and 9(0.4g) regions frames.(4) For the frame in intensity 8 regions, the variation of the axial load considering the vertical ground motion is more significant than those in the intensity 7 region. The intensity 8 region frames was mainly beam-hinge mode under horizontal ground motion only. However, the column hinges notably increased on the lower store under combined horizontal and vertical ground motion. The frame is more likely to develop the beam-column hinge mechanism, in which the beam hinge is the key hinge mechanism and the lower store of the structure is more likely to develop the weak part. So the vertical ground motion should not be neglected when the frame is in intensity 8 region. The more reasonable sesmic measures should be carried out to achieve reliable strong column-weak beam failure mode.