双塔钢桁斜拉桥斜拉索破坏动态响应

Dynamic response of cable breakage in double-tower cable-stayed bridge with steel truss girder

针对斜拉索在使用过程中的失效可能导致斜拉桥承载力下降的问题,提出反向加载模拟斜拉索断裂的作用效应,通过不同的加载时间模拟拉索破坏的时间和对整体结构的激励,分析斜拉索在不同断裂时间下的斜拉桥动力响应特征;并根据美国PTI《斜拉桥设计指南》中对斜拉索断裂的相关规定,提出单根斜拉索断裂对负载斜拉桥影响的计算方法,即对结构自重和汽车活载的放大。研究结果表明:提出的方法较准确地模拟了斜拉索断裂及其对整体结构的冲击作用;整体结构的动力响应随击振时间T_d的变化而改变,当T_d大于整体结构的自振周期时,结构在击振期间会出现显著动力响应;当T_d小于整体结构的自振周期时,结构的最大动力响应出现在击振完成后的自由振动期间;根据PTI中对斜拉索断裂造成的全桥荷载放大作用,也较为真实地分析了其作用最大值,斜拉桥在拉索破坏反向放大荷载、恒载及车道分布荷载组合作用下,主梁最大位移出现在中跨跨中附近,与相同汽车荷载分布下完好结构的最大竖向位移差值出现在中跨跨中附近;距离主塔及支座越远,所受影响越大;与完好结构索力最大差值出现在失效拉索的相邻索。提出的方法进一步验证了在PTI中根据拟静力法求得的单索破坏造成的最大动力放大系数2.0是合理的,但如果考虑2根以上斜拉索同时失效,则根据2.0的动力放大系数进行安全储备设计是不足的。

For the problem that failure of decline in bearing capacity of cable-stayed to simulate the effect of cable breakage. incentive to the whole bridge with differen cables in the process of using may lead to a serious bridges, this paper proposed a reverse loading method Through simulating the time of cable damage and t loading time, the dynamic response characteristics of cable-stayed bridges caused by different breakage time were analyzed. According to the relevant regulations on cable breakage in recommendations of stay cable design, testing and installation of PTI （Post-Tensioning Institute） in American, a calculation method of the effect of single cable breakage on the loaded cable-stayed bridge was put forward, that is, the amplification of structural weight and the live load of automobile. The results show that the method of reverse loading is more accurate to simulate the breakage of cables and the impact to the whole structure. The dynamic response of the whole structure varies with the change of shock time Td. When Ta is larger than the natural vibration period of the whole stricture, the most obvious dynamic response of the structure will occur during the shock period, when Td is smaller than the natural vibration period of the whole stricture, the most obvious dynamic response of the structure will occur during the free vibration after the shock. On the other hand, the maximum value of the action is also analyzed more realistically according to the amplification of the full-bridge load caused by the cable breakage in PTI recommendation. Under the load combination of reverse amplification load, dead load and the driveway distribution in cable failure of cable-stayed bridge, the maximum displacement of main girder appears in the area of the span center of mid-span. Under the same vehicle load distribution, the maximum difference of vertical displacement appears near the span center of mid-span, compared to the intact structure. The farther the distance from tower and supporter, the greater the impact is. The maximum difference between the intact structural cable force appears in the adjacent cable of the failure cable. And it further verifies that the maximum dynamic amplification coefficient 2.0 due to the single cable damage obtained by the quasi-static method in PTI recommendation is reasonable. However, if the failure of more than two cables are considered at the same time, it is insufficient to design the safety reserve according to the dynamic amplification coefficient 2.0. 2 tabs, 7 figs, 25 refs.