Local Detailed Analysis On The Key Parts Of Long Span Combined Road And Railway Plate-truss Composite Cable-stayed Bridge

The main bridge of Fenfangwan Yangtze River Bridge is a combined road and railway plate-truss composite cable-stayed bridge with span arrangement (60.5+156+464+156+60.5)m which uses orthotropic steel deck combined with the truss. It has the structural characteristics of both orthotropic steel deck and plate-truss composite structure which make its stress to be complex. In the finite element analysis of the whole bridge, details are difficult to be simulated, so we can’t get the accurate stress level of the key parts. Therefore local detailed analysis of the important parts is necessary. The main work and research achievement as follows:1、According to the results of analyzing the whole bridge, four key parts were choosed as the objects of local detailed analysis. Then this paper determine calculation method includes interception range, modeling method and boundary conditions. Considering all details of structure,four accurate finite element models were made by using finite element analysis software ANSYS.2、Local detailed analysis of highway steel deck segment which contains cable anchorage joints SJ1and SJ2has been done. In this segment, the cable force and axial force of deck system are the largest. According to analysis, in the most area of the segment the Mises equivalent stress and principal tension stress level are low. But stress concentration happened in small area near U-shape reinforcing ribs hole chiseled on the web of Lateral beam which connected with cable anchorage joints. The maximum Mises equivalent stress and principal tension stress is366MPa and116MPa exceeding the yield strength of Q345steel and fatigue allowed stress amplitude of the Ⅷ type of structure required by design codes.3、Local detailed analysis of railway steel deck segment which contains bottom chord joints XJ1and XJ2has been done. In this segment, the axial tension force of diagonal tie and axial force of deck system are the largest.According to analysis, in the most area of the segment the Mises equivalent stress and principal tension stress level are low. But stress concentration happened at the connection of bottom chord and bottom flange of lateral beam. The maximum Mises equivalent stress and principal tension stress is355MPa and96.3MPa exceeding the yield strength of Q345steel and fatigue allowed stress amplitude of the Ⅷ type of structure required by design codes. 4、Local detailed analysis of cable anchorage joints SJ1in which cable force is the largest has been done.In the most area of the joint, the Mises equivalent stress and principal tension stress level are low. But stress concentration happened at the cross connection of diagonal tie web and web of lateral beam which belongs to the top layer deck. The maximum Mises equivalent stress reached to361-720MPa and principal tension stress is216MPa far exceeding the yield strength of Q345steel and fatigue allowed stress amplitude of the Ⅷ type of structure required by design codes.5、Local detailed analysis of bottom chord joints XJ1has been done. In this joint, axial tension force of diagonal tie and axial compression of bottom chord are the largest. In the most area of the joint, the Mises equivalent stress and principal tension stress level are low. But stress concentration happened at the connection of diagonal tie and outside web of bottom chord. The maximum Mises equivalent stress and principal tension stress is231MPa and110MPa exceeding the fatigue allowed stress amplitude of the Ⅶ type of structure required by design codes.6、According to calculation results advice has been sent to designing institute. The research result of this paper also has reference value for the bridge of similar type.