沌口长江公路大桥加劲梁选型与设计

Stiffening Girder Type Selection and Design for Zhuankou Changjiang River Highway Bridge

沌口长江公路大桥主桥为(100+275+760+275+100)m双塔双索面半飘浮体系斜拉桥。针对该桥车道数较多、通行重载货车比例高的特点,提出整幅式P-K断面钢箱梁、双层钢桁梁以及分幅式钢箱梁3种加劲梁方案,采用有限元软件分析各方案静动力性能,综合考虑各方案静动力性能、景观效果、造价等,确定该桥选用整幅式P-K断面钢箱梁方案。该方案钢箱梁由2个流线型扁平边箱、箱间顶板及横隔板组成,宽46.0m,中心线处梁高4.0m,横隔板采用整体式(标准间距3.0m);剪力滞和横向偏载效应导致的截面应力不均匀及局部应力增大,通过分段调整钢箱梁板厚以及加强局部构造,使钢箱梁应力在容许范围内;针对大跨重载的特点,采用了疲劳细节等级较高的构造细节,加强了桥面板与加劲肋的焊缝设计,提高了钢箱梁正交异性钢桥面板的疲劳强度。

The main bridge of the Zhuankou Changjiang River Highway Bridge is a two-pylon cable-stayed bridge of half-floating system.The bridge has span arrangement of（100＋275＋760＋275＋100）m and the stay cables are fanned out in double cable planes.To meet the special demands of the bridge,like accommodating multiple traffic lanes and carrying large ratio of heavilyloaded vehicles,three stiffening girder schemes were proposed,including the monolithic steel box girder with P-K（Pasco-Kennewick）section,double-deck steel truss girder and separated twin steel box girders.The finite element software was used to analyze the static and dynamic properties of each scheme.The monolithic steel box girder with P-K section was finally chosen,based on the comparison of the three schemes from the aspects of static and dynamic performance,landscape effects and costs.The girder type determined consists of two stream-lined flat edge boxes and the in-between connecting top plates and diaphragms,and is 46.0mwide and 4.0mdeep at the bridge central line.The diaphragms are integral,installed at 3.0 mintervals.The shear lag effect and transverse eccentric load will cause non-uniform stress distribution in the sections and local stress increase in some locations,but the stresses in the steel box girder can be controlled within the allowable range by adjusting the plate thickness of the steel box girder segment by segment and strengthening the local structural components.Because the bridge has long spans and has to carry heavy loads,the structural components with higher fatigue resistant grade are chosen,the welding joints between the bridge deck and stiffening ribs are strengthened,with the intention of improving the fatigue strength of the orthotropic steel deck of the steel box girder.