大跨度钢桁拱桥关键节点受力特性及优化研究
Mechanical characteristic and optimization study on key joint of long span steel truss arch bridge

横琴二桥是国内跨度最大、桥面最宽的公路钢桁架拱桥，孔跨布置为：100+400+100=600 m。桥下拱肋与下弦杆交汇处的节点(E9节点)采用焊接整体节点，节点板将主桁相关杆件和桥面纵、横梁连成一体，各构件内部加劲肋众多，形式、尺寸多样，节点的结构构造和受力状态复杂。在全桥空间有限元分析的基础上，选取具有代表性的E9节点和2个最不利的主力组合工况，完成局部精细有限元分析。研究结果表明：2个工况下E9节点各相关杆件绝大部分区域应力水平较低，Mises 等效应力小于200 MPa，局部区域应力集中程度较严重，应力水平超出了弹性范围。针对拱内下弦杆变截面处出现的高应力区域的情况提出改善措施，建议在该位置增设一道环形横隔板，该方案可不影响下弦杆内的柔性系杆通过。增设横隔板后，变截面处的应力集中现象得到明显改善，应力水平在弹性范围以内。
Hengqin second bridge is a highway steel truss arch bridge with the largest span and the widest deck in China. The span of the bridge is 100+400+100=600 m. The welded integral joint E9 was located at the junction of the lower arch rib and the lower chord. By using two connecting plates, the relevant truss bars and cross beam of the floor beam are welded as a whole. The internal structure construction of the joint is very complex. Many stiffening ribs of various kinds and scale are arranged inside every components. Refined finite element analysis is completed for the representative E9 joint and the two worst load cases of main loads combination based on 3D finite element analysis of the whole bridge. The results show that the stress level of most areas of the relevant components of E9 joint are not high, and their Mises equivalent stress is less than 200 MPa. However, 5 small regions exist where bear severe stress concentration are beyond yield stress. A circinate diaphragm is proposed to reduce the stress level of the varying section of the lower chord. This measure does not affect the work of flexible tied bars. The results of local refined finite element analysis show that stress concentration is solved and the material remains in the elastic state with diaphragm added