Research On Seismic Behavior Of Portal-frame Tower Of Single Tower Cable-stayed Bridge

As span becomes longer, bridge deck becomes more flexible and structural complexity increases, cable-stayed bridge seismic performance study has become one of the most concerned and challenging issues in engineering. Bridge seismic study aims to ensure bridge structure has adequate security to stand against the basic earthquake, and provide effective measures and scientific basis for the bridge seismic design. Cable-stayed bridge tower is one of the most important structures to bear load, therefore its performance is critical to determine whether the bridge can withstand seismic loads and other loads or not. Especially for single tower cable-stayed bridge, tower is the main structure to withstand seismic load, therefore the seismic analysis of bridge tower is of great significance.This dissertation discusses the analysis theory and methods of seismic response of cable-stayed bridge, using SAP2000, a general structural finite element program, by response spectrum method, linear dynamic time-history analysis method and nonlinear dynamic time-history analysis method to analyze bare tower and tower in cable-stayed bridge comprehensive, and then study the differences of the result of response spectrum analysis and linear dynamic time-history analysis, study the different properties of bare tower and tower in cable-stayed bridge.It is found that the dispersion of tower response results which using seismic waves fitted by velocity response spectrum as input waves is very small. The seismic response is similar of bare tower and tower in cable-stayed bridge in transverse direction. But in longitudinal direction, it is very different. In cable-stayed bridge, compared with bare tower, the internal force in the lower tower column and upper tower column divided by bottom beam suddenly changes. The internal force in the lower tower column increase greatly and internal forces decreased in the upper tower column. As can be seen, the bridge tower during the construction period and service stage in the earthquake, its vulnerable parts differ.In order to find the vulnerable parts of the bridge tower in development, plastic analysis is carried out. Results show that, in longitudinal strong earthquake, the yield point of bare tower is in the upper tower column in longitudinal direction, but in cable-stayed bridge, the yield point is in the lower tower column. It is similar to linear analysis result. In transverse strong earthquake, the yielded parts are beams in the two models, and there is no yielded phenomenon in tower columns.