Study On The Spatial Stress And Nonlinearity Of Extradosed Cable-stayed Bridge

Extradosed Cable-stayed Bridge is a transitional bridge between cable-stayed bridge and continuous girder bridge.Its structure is similar to a cable-stayed bridge,the cross section of the box girder is similar to a continuous beam bridge.In recent years,it has been vigorously developed in the main span of 100 ~ 300 m,with the structure type of wide box girder and single cable plane as the main type.The advantages of this structure are low cost and easy construction.However,due to the shape of wide box girder and single cable plane,the anchorage points of the cables on the box girder are concentrated in the center of the box girder,which results in the local stress being too high.This article takes Jingyuan Jintan Yellow River Bridge as the background and conducts the following research work from the whole to the part:(1)Describes the current development of extradosed cable-stayed bridge.Statistics on the structural characteristics of currently built extradosed cable-stayed bridge.It is concluded that the currently constructed extradosed cable-stayed bridge are dominated by the structure type of single cable planes of wide box girder consolidated with bridge towers and box girder.(2)Based on the design parameters and construction methods of the background bridge,a full bridge finite element model was established using midas-civil,the internal forces and deflections of the key construction stages were discussed,and the safety during the construction stage was ensured with reference to the specifications.In addition,a series of discussions were made on the internal force changes of the main beam during the closing process,and the changes in the internal force of the main beam during the 10-year concrete shrinkage and creep.(3)For the background construction to the last cable stage,a 1/2 solid element model was established using midas-FEA.The stress distribution of the box girder under the action of the horizontal cable tension,the vertical cable tension and the dead weight are analyzed.The results of the stress analysis of the solid element are extracted and compared with the results of the stress analysis of the beam element.There is a certain deviation between the calculation results of the solid element and the beam element,especially the stress distribution of the box girder is very uneven under the horizontal cable tension.The stress distribution of the box girder under the vertical component force and the dead weight is more evenly distributed.Through comparative analysis,it is also found that at the position where the cross section is abrupt,the calculation result of the beam element does not accord with the actual situation.(4)Derive the calculation formulas for the cable elastic cable length,cable elastic elongation,and cable unstressed length cable characteristic values with the cable inclination angle as the main parameter through the catenary equation,and derive the cable beam End tension and elastic cable length are two iterative formats with known quantities.Taking the background bridge as an example,the analytical solution and finite element analysis are compared to prove the correctness of the formula,and the iteration speed is fast and the accuracy is high.(5)By comparing the errors between the parabolic theory and the catenary theory in calculating the nonlinearity of the cable,it is found that the errors between the two are closely related to the cable inclination,cable length,and cable stress level.The maximum error is about two degrees.It is recommended to use the catenary theory to analyze the cable nonlinearity when the cable length exceeds 300 m and the cable stress is lower than 200 MPa.