Investigation On Structural Performance And Progressive Collapse Of A Long-span Concrete Cable-stayed Bridge Subjected To Cable Loss

Cable-stayed bridge are composed of three main components: the cables,the stiffening girder system and the pylons.As the key member of cable-stayed bridge,the cables are more likely to fail during the bridge construction and operation.The failure of cables in the bridge may cause the redistribution of internal force and dynamic impact of the overall structure,potentially leading to a progressive failure.Therefore,the static and dynamic performance of a cable-stayed bridge subjected to cable loss is critical and should be evaluated to prevent progressive collapse caused by the failure of portions of cables in the bridges.All the existing research so far,however,rarely studied the structural performance of cable-stayed bridge during the multiple-cable loss,the relationship between the failure of portions of cables and the collapse of the overall structure were not clear.Therefore,this paper conducted investigations on the structural performance and progressive collapse of a long-span concrete cable-stayed bridge subjected to multiple-cable loss based on the financial support of program “Theories and methodologies for structural design and wind-induced catastrophe of super-long span cable-supported bridges with high performance materials(National Natural Science Foundation of China,No.51938012)”,“Research on the impact performance of CFRP cable and anchor system(National Natural Science Foundation of China,No.51478177)” and the fire accident of the Chishi Bridge.The research mainly includes following studies and draws conclusions as follows:(1)Field inspection on structural performance of a long-span concrete cable-stayed bridge subjected to multiple-cable loss.To investigate the behavior of the Chishi Bridge subjected to nine-cable loss caused by a fire accident,a field inspection was conducted,focusing on the post-accident of the bridge in terms of metrics including the cables,the girder and the pylon.The damage of the entire bridge structure and the structural components was observed,and the structural performance of the Chishi Bridge subjected to nine-cable loss was assessed.(2)Static performance of a long-span concrete cable-stayed bridge subjected to multiple-cable loss.A nonlinear finite element(FE)model for determining the structural behavior of cable-stayed bridge subjected to cable loss was developed using the software Abaqus,considering the geometrical and material nonlinearity of the bridge structure,and the calculated results was verified by the corresponding results from the field inspection.With the verified model,a comprehensive numerical investigation of the static performance of the bridge during the entire cable loss and restoration process was conducted.The maximum internal force of the girder,the maximum tensile stresses in the remaining cables and the prestressed tendons,and the maximum compressive stress in the concrete girder were obtained to assess the structural performance.(3)Dynamic response of a long-span concrete cable-stayed bridge subjected to multiple-cable loss.Considering the dynamic impact of bridge structure subjected to cable loss,a nonlinear dynamic FE model of cable-stayed bridge was developed based on the verified static FE model.The influence on the structural dynamic response of the cable breakage time was analyzed,and the corresponding cable breakage time for both dynamic and quasi-static cable loss event was determined.A comprehensive numerical study was then conducted to analyze the dynamic behavior of the cable-stayed bridge throughout the multiple-cable loss process.With the calculated results,the maximum dynamic response of each component in the bridge structure was investigated,and the corresponding dynamic amplification factor(DAF)was then proposed: the DAF of the maximum torque,longitudinal and transverse bending moment of girder during the accident are 1.09-1.55,1.21-1.65 and 1.21-1.76,respectively,the DAF of maximum displacement is ranged from 1.03 to 1.75,the DAF of maximum principal compressive stress are 1.02-1.58;the DAF of the tensile stresses in the prestressed tendons and remaining cables are 1-1.9 and1.05-1.4,respectively;the DAF of the longitudinal displacement of the pylon top is ranged from 1.23 to 1.65.(4)Analytical calculation method for analyzing the response of cable-stayed bridge subjected to cable loss with transfer matrix method.A mechanical model of three beams with discrete springs for determining the dynamic and static performance of the cable-stayed bridge subjected to cable loss was developed and calculated by the transfer matrix method.The dynamic and static response of a cable-stayed bridge determined from the aforementioned methods was verified by the results of a validated finite element model.Therefore,the aforementioned mechanical model can be used in the parametric analysis of structural behavior of cable-stayed bridges subjected to cable loss.(5)Collapse analysis of a long-span concrete cable-stayed bridge subjected to multiple-cable loss.The vulnerability analysis method of cable-stayed bridge to cable breakage was developed,the vulnerability factor of bridge structure subjected to different cable loss events was then investigated with the relative area magnitude of broken cable to total cable and the cable tension transfer factor as two parameters.Then,a multiscale nonlinear dynamic FE model for investigating the whole failure and collapse process and the collapse failure modes of a cable-stayed bridge subjected to different cable loss events was developed using software Abaqus/Explicit.The bridge structural collapse criterion was then proposed based on the ratio of total energy to external work of force.It was suggested that when the energy ratio was less than 0.85,the collapse stage of cable-stayed bridge subjected to cable loss could be determined.