三塔超大跨公铁两用斜拉桥活载加载标准研究

为探究公路铁路活载对三塔超大跨公铁两用斜拉桥结构的影响,以某公铁长江大桥为研究背景,建立有限元全桥模型。利用影响线确定活载最不利加载位置,分析铁路活载和公路活载对主梁、主塔、斜拉索的影响。研究结果表明:随着铁路和公路活载加载长度的改变,桥梁结构响应在主梁竖向位移、主梁压应力、主塔顺桥向位移、主塔顺桥向弯矩、斜拉索索力增幅等方面表现出一定的规律性,铁路活载引起的桥梁结构响应是公路活载的3.2~4.2倍;对于主梁和主塔,当铁路活载加载长度分别增加5.4%、22.2%、18.2%,结构响应对应增大35.90%~36.90%,8.27%~13.07%,4.40%~8.38%;对于斜拉索,活载作用下索力最大增幅位于跨中附近;按照偏安全的到发线长度加载比按照列车可能最大长度加载,在桥梁设计上更具有安全冗余度。研究成果可为超大跨度铁路桥、公铁两用桥的设计提供参考。

Research on Standard of Live Load Applying to Three-pylon Very-long-span Road-rail Cable-stayed Bridges

In order to understand the impact of the live loads of roads and railways on the structure of three-pylon very-long-span road-rail cable-stayed bridges,this paper builds a finite element bridge model based on the case of a Yangtze River road-rail bridge.It determines the most unfavorable applying position of live loads using the impact line,and analyzes the impact of live loads of the railway and the road on the main girder,main pylons,and stay cables.The results are as follows:With changes in the length along which live loads of the railway and the road are applied,the response of the bridge structure shows a certain regularity in terms of the vertical displacement of the main girder,the compressive stress of the main girder,the displacement of the main pylons along the bridge,the bending moment of the main pylons along the bridge,the increase of stay cable force,and the response of the bridge structure caused by railway live load is 3.2-4.2 times that caused by road live load;As for the main girder and main pylons,when the applying length of railway live load increases by 5.4%,22.2%and 18.2%,the response of the structure increases by 35.90%-36.90%,8.27%-13.07%and 4.40%-8.38%accordingly;As for the stay cables,the maximum increase of cable force under the live load is near the mid-span;If the load is applied based on the safe arrival&departure track length ratio and the maximum possible length of train,the safety margin of the bridge design is about 40%.Research achievements may provide reference for the design of very-long-span railway bridges and road-rail bridges.