武汉青山长江公路大桥主桥荷载试验有限元分析

Finite Element Calculation Analysis of Load Tests on Main Bridge of Qingshan Changjiang River Highway Bridge in Wuhan

武汉青山长江公路大桥主桥为主跨938 m的双塔双索面全飘浮体系斜拉桥。为确定该桥静载试验控制截面及自振特性试验测点布置,采用MIDAS Civil软件建立全桥有限元模型,分析桥梁在8车道汽车活载作用下的结构内力及自振特性。结果表明:主梁主跨最大弯矩截面位于跨中偏北塔约44.5 m处、应力最大截面对应最大正弯矩截面、最大竖向位移截面位于跨中处,南塔最大弯矩截面位于桥塔根部;桥梁模态振型以主梁纵飘、一阶面内纵弯与横弯、桥塔横弯为主。根据静、动力分析结果,按照结构最不利受力及代表性原则,静载试验共确定8个主梁测试截面和2个桥塔测试截面;按照计算振型特征并结合现场实际情况,自振特性试验共确定44个主梁自振特性测点及8个南塔测点。

The main bridge of Qingshan Changjiang River Highway Bridge in Wuhan is a two-pylon cable-stayed bridge of a full-floating system.The bridge has a main span of 938 m,with stay cables fanned out in double cable planes.To determine the control cross-section for the static load test and lay out the testing points to examine the natural vibration characteristics of the bridge,the software MIDAS Civil was used to build the finite element model of the full bridge,to analyze the internal forces and the natural vibration characteristics of the structure under 8 lanes of vehicle live loads.The results demonstrate that the cross-section with maximum bending moment in the main span girder occurs at the location about 44.5 m from the midspan to the north pylon,the cross section with maximum stress corresponds to the cross-section with the maximum positive bending moment and the cross-section with maximum vertical displacement appears in the midspan.For the north pylon,the cross-section with maximum bending moment is located at the root of the pylon.The predominant vibration modes include longitudinal floating,the first-mode in-plane longitudinal and transverse bending of the main girder as well as the transverse bending of the pylons.Based on the results of dynamic analysis,a number of 8 testing cross-sections for the main girder and 2 testing cross-sections for the pylons were determined by the static load test,conforming to principle of selecting the unfavorable loading and representative loading conditions of the structure.And based on the vibration characteristics gained from calculation and together with the actual condition at the bridge site,a number of 44 testing points to examine the natural vibration characteristics of the main girder and 8 testing points to observe the natural vibration of the south pylon were determined.