Twin Towers Three-span Single Cable Plane Concrete Cable-stayed Bridge Main Beam Wider Segment Behavior Analysis And Model Tests

The ZCD Bridge is a single cable plane cable-stayed bridge with double towers and six highway lanes. The girder of the bridge is fixed rigidly to the towers, and two auxiliary piers are set separately in each side span. The span arrangement is (36+70+248+70+36) m. Because of the special geographical position, a girder segment with a length of 63.5m at the west side span is designed with variable width. The width of the deck changes gradually from 42.07m to 33.0m, and the cross section changes gradually from single box five cells to single box three cells. This kind of design is creative, and the stress state of the girder is very complex. Mechanical behavior of the variable width girder segment was studied systematically in this thesis by means of FEM analysis and model test. The major work is summarized as follows:1.Based on the space bar-system FEM analysis of the whole bridge, mechanical behavior of the variable width girder segment was analyzed by space local refined FEM under dead load and live load. The length of the test segment was determined according to the theoretical analysis results and actual situation of the testing laboratory.2.Simulation method of the cables, boundary conditions and deck load were studied. That is to divide the cable force into two.One is horizontal, and the other is vertical.The horizontal force was simulated by tensioning prestressed tendons which were arranged in the mid cell of the box girder, and the vertical one was simulated by the reaction force which was generated by the elastic beams arranged under the bottom deck of the girder when the model was loaded. Stress state of the variable width girder segment was simulated by the synchronization of the cable force and the deck load.3.A 1:4 test model was designed and produced, and FEM analysis was finished under several load conditions for this model.The theoretical analysis results of the test model and the variable width girder segment were compared, and the results show that the stress level of the former is very close to the latter under all load conditions.This indicates that the test program was designed correctly, and the model test can simulate the stress state of the real bridge very well.4.Four symmetric load cases and three eccentric load cases were completed, and the results of symmetric test and eccentric test were compared. The results show that the test model was on linear elastic state all the time, and the test values show good agreement with the theoretical analysis under all load conditions.Stress state under symmetric load is worse than that under eccentric load of the variable width girder segment.The research results of this thesis not only provide the basis for design and construction of The ZCD Bridge, but also provide references for study of other similar bridge structures.