大跨度板桁组合梁温差效应分析

为避免环境温度特别是日照变化对板桁组合梁的不利影响,以九江长江大桥第三联(180+216+180)m三跨刚性梁柔性拱结构为例,对其钢结构表面温度及联端活动支座位移进行现场实测,并采用MIDAS Civil软件建立有限元模型对板桁组合梁的温差效应进行分析。结果表明:板桁组合体系在太阳辐射影响下温差效应明显,特别是在受到不同角度辐射时板桁间温差及上、下游温差明显,这也是导致板桁温差效应的直接原因;由于正交异性钢桥面板与桁架体系的刚度差异,在结构温差影响下板桁间纵、横向相对位移及局部应力较大。基于此提出改变支座体系、改变连接方式、设置伸缩缝3种处理板桁效应的方案,各方案需要根据不同情况适当选择,九江长江大桥采用改变支座体系的方案有效解决了该桥的板桁温差效应。

Analysis of Temperature Difference Effect of Long-Span Plate-Truss Composite Girder

In order to avoid unfavourable influences of ambient temperature, especially sunshine, on the plate-truss composite girder, taking the third continuous unit of Jiujiang Changjiang River Bridge which consists of (180+216+180) m three-span rigid girder flexible arch structure as an example, we performed the field measurement for the surface temperature of steel structures and for the displacements of movable supports of continuous unit ends, and analyzed the temperature difference effect of plate-truss composite girder by establishing a finite element model using the MIDAS Civil software. The results show that the temperature difference effect of plate-truss composite system is obvious under the influence of solar radiation, especially when radiated from different angles, the temperature differences between plate and truss and between upstream and downstream are obvious, which is also the direct reason for the temperature difference effect of plate-truss. Due to the stiffness difference between the orthotropic steel bridge deck and the truss system, the longitudinal and transverse relative displacements and local stresses of the plate-truss are remarkable under the influence of the structural temperature difference. Thereby, we propose three schemes, including changing the support system, changing the connection mode, and setting expansion joints, to deal with the plate-truss effect. Each scheme should be properly selected according to different situations. The temperature difference effect of plate-truss can be effectively solved by changing the support system for Jiujiang Changjiang River Bridge.