大跨度钢桁拱桥拱桁交叉节点疲劳试验研究

Fatigue Tests of Arch Truss Cross Joints of Long-span Rail-cum-road Bridge

大跨度公轨两用桥拱桁交叉节点处汇交杆件多、形状复杂、规模大、受力集中,处于典型的复杂空间受力状态。本文介绍根据疲劳损伤累计理论确定疲劳试验荷载的过程,得出疲劳荷载主要取决于下层汽车荷载和地铁荷载的结论。设计并制作1∶4缩尺模型,对该模型进行200万次疲劳加载试验。试验结果表明:结构应力水平较低,最大主拉应力为28.5 MPa,最大Von.Mises应力为45.1 MPa。在完成循环加载200万次后,试验模型未发现裂纹,逐步提高荷载幅,循环加载276万次,试验模型未发现裂纹,可得出重庆朝天门大桥的拱桁交叉节点连接结构在正常养护维修情况下,设计寿命期内不会发生疲劳开裂,疲劳强度满足要求。

The arch truss cross joints of a long-span rail-cum-road bridge are in the complex spatial-stressing situation where interaction rods are of a great number,of complex configuration and in high stressing concentration.Loading in fatigue tests is decided on the basis of the cumulative fatigue damage theory,and the result of the fatigue load is mainly controlled by the subway load and the low-deck truck load.The 1∶4 scale model was designed and manufactured.The fatigue test model was applied with cyclic loads by two million times.The test results show that the stress level is low,the maximum principal tension stress is 28.5 MPa and the maximum Von.Mises stress is 45.1 MPa.No cracks are found in the test model until 2.76 million times of cyclic loading.So it can be seen that for the arch truss cross joint structure of the Chaotianmen Yangtze River Bridge in Chongqing,the requirements for the fatigue strength are satisfied and fatigue cracking will not happen in the designed life under normal maintenance.