Study On Seismic Behavior Of RC Frames Under Horizontal And Vertical Seismic Excitation

According to present codes, the vertical ground motion is not considered in the lowand medium intensity regions. However, the ratio of the vertical component andhorizontal component of the ground action in high intensity region is0.65, witch isdemonstrated insufficient by seismic records. Taken several RC frame structures as theobjects of the research, four multilayer reinforced concrete frames were designed. Byusing the finite element software ABAQUS, the plane frame models were built and theelasto-plasticity time history analysis was applied to compare the results of the analysisunder horizontal ground motion with that under combined horizontal and verticalground motion. In this paper, the displacement responses, the variation of internal force,the variation of bearing capacity and the distribution of plastic hinges of the framesconsidering vertical ground motion were evaluated to analysis the affection to failuremode and seismic performance by considering vertical ground motion. The conclusionsof this paper are as following:①For the seismic displacement responses of the frames of all intensity regions,the vertical ground motion has no significant effect on the topmost displacement, theinter-story displacement angle and story displacement.②The axial loads of the columns varies significantly considering the action ofvertical ground motion under rare earthquake. Comparing with inputting horizontalground motion only, the peak value of the axial loads of exterior column increased wheninputting combined horizontal and vertical ground motion and the variation of the peakvalue of interior column was particularly significant.③For the intensity7(0.1g) region frame, the vertical ground motion broughtevident variation of the axial load, but the influences on seismic performance was notthat significant than that of high intensity regions. The occurrence of the tension forcewas less and the tension force was small. According to new seismic code, the bendingcapacity of the column of intensity7region frame is further strengthened, the bearingcapacity of the column is well guaranteed. For the intensity9(0.4g) region frame, thebending capacity of the column is calculated by actual reinforcement of the beam, so thebearing capacity has a reliable guarantee and the action of combined horizontal andvertical ground motion did not change the developing and distribution of thecolumn-hinge of the frame. Considering the combined horizontal and vertical ground motion do not bring disadvantageous influences on yielding mechanism and failuremode to intensity7(0.1g) and9(0.4g) regions frames.④For the intensity8region frame, the variation of the axial load considering theaction of vertical ground motion was more significant that in the intensity7region. Thismay bring about the quantity of beam-hinge changed a lot comparing with that underhorizontal ground motion only. The intensity8region frames was mainly beam-hingemode under horizontal ground motion only while the column hinges notably increased,especially the significant increase of plastic hinges at middle floor columns undercombined horizontal and vertical ground motion. The frame was more likely to form amechanism of beam-column hinge of which the column hinge was principal and themiddle part of the structure was more likely to be the weak part. Therefore, the verticalground motion should not be neglected to the design and analysis of intensity8regionframe. The more reasonable sesmic measures should be considered to achieve reliablestrong column-weak beam failure mode.