Study On Safety And Durability Of Arch Bridge Suspender System Considering Vehicle-bridge Coupling

The arch bridge structure has gained an increasing attention in bridges construction recently. Its safety and durability become more and more prominent with the most concern on suspender systems in the half through arch bridge and through arch bridge.Many arch bridge collapse accidents happened in recent years are mostly resulted from the failure of the suspender system. Survey on many suspender system accidents shows that the dominated reason is caused by the failure of the short suspender, or initiated by the fracture of the short suspender in some case. There are many reasons related to the durability of the suspender system, such as corrosion and fatigue. Generally, it is reasonable to assume that all the suspenders in the same bridge are exposed to the same environment. Therefore, the difference of durability between the long and short suspender can be attributed to dynamic effect induced by the vehicle load. It is necessary to study the safety and durability of the suspender system of arch bridge through detailled analysis. In this work, considering vehicle-bridge coupling, the failure mechanism of suspender system especially the short suspender were researched, the design method to enhance the durability and to assure the safety of suspender system were investigated. The primary contents are as follows.Firstly, a dynamic analysis model considering vehicle-bridge coupling was built. A three dimensional finite element model for the large span arch bridge, a space multi-axial vehicle model and a road roughness model were built individually. The dynamic analysis of vehicle-bridge coupling was calculated by the above three models.The dynamic analysis model considering vehicle-bridge coupling was validated by a comparison between the calculated static and dynamic response of an arch bridge with the measured results by a bridge loading test.Secondly, based on the proposed dynamic analysis model considering vehicle-bridge coupling, the dynamic response of the suspender system was analyzed.The effect of weight, speed, acceleration of vehicle and road roughness on dynamic response of the suspender system was studied by analyzing the dynamic stress caused by impact and bending of the suspender. The results show that impact and bending has a significant effect on the dynamic response of the suspender system. As a result, a large stress amplitude and significant non-uniform stress distribution emerge on the cross section of suspender caused by vehicle load, which induces a premature fatigue failure of the suspender system. It should be pointed out that the stress within the short suspender is much higher than that within the long suspender, which indicates that impact loading caused by vehicle affects more to the short suspender to lead to its early failure.Then, based on the mechanism of short suspender fatigue failure, an equal stiffness model of the suspender system was proposed to improve its durability. By designing axial stiffness of the suspender system, stresses within the short suspenders under vehicle load are improved to enhance its impact resistance. Fatigue life of the short suspender is prolonged. Furthermore, durability of the whole suspender system is enhanced. At the same time, base on the simultaneous distribution model of vehicle speed and weight built by the actual monitoring traffic statistic model, the traffic flow loads are built and the durability of the suspender system designed by equal stiffness model is evaluated by analyzing the vehicle load.Finally, in view of the problem that the fatigue failure of the suspender system is hard to monitor,a new double suspender system model with an added early-warning suspender which has early-warning and fail safety function was proposed and the design method for fatigue life was discussed. The proposed suspender system has the following performance by service life design. (1) The service life of early-warning suspender is reasonably and economically inferior to that of working suspender. (2) The working suspender is secure with the eraly-warming suspender being broken. The fatigue lives difference between the early-warning suspender and the working suspender was implemented by appling an initial stress to the early-warning suspender. Fatigue life under the vehicle load was further calculated to evaluate the early-warning function.Moreover, the effect of damage of the suspenders system on its fatigue life difference was studied, the early-warning and fail safety function of the double suspenders system model was then evaluated.