| Through the statistical analysis of the earthquake hazard, it can be seen that the vertical motion was too large to be negligible in some earthquake. The analysis of structural responses subjected to horizontal and vertical earthquake excitation has attracted attention recently. The object of the thesis is to study the effects of vertical seismic on the earthquake resistance behavior of the frame and its components.In this thesis, two R/C frame structures under vertical and horizontal seismic excitation were analyzed with the elastic-plastic time history analysis. The first one was one story and one span and the second one was five stories and one span. The time history analysis was carried out in two seismic wave input cases, one with both horizontal and vertical wave input and the other with horizontal input only. Comparison on the dynamic response of structures for case of single direction seismic wave and for case of two direction seismic waves was made. The R/C frame structures were modeled with bar systems. The column was modeled with multi-spring. The concrete and steel bars in column were considered as springs in order to reflect the coupling influence between the axial force and the moment-rotation relationship, the hysteresis of springs based on the material properties. The moment-rotation relationship of beam section was modeled with the trilinear hysteresis model. Two kinds of the earthquake waves were adopted in the thesis, i.e. EL-CENTRO wave and Kobe wave.According to the investigation of the analytical results, it can be seen that the vertical seismic excitation may enhance the vertical displacement and the bending moment at mid-span of the beam, but have little effect on the variation of the axial force and ultimate carrying capacity of column. The increase of bending moment at mid-span of the beam by vertical seismic excitation and internal force redistribution is proposed to be taken into account when the R/C frame structure has a comparative span.
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