钢桁腹-混凝土组合箱梁局部外接节点静载试验及极限承载力计算研究

Static Load Tests and Ultimate Load Bearing Capacity Calculation of Local External Joints of Concrete Box Girders with Steel Truss Webs

为了解钢桁腹-混凝土组合箱梁(顶、底板为混凝土结构,腹杆为钢结构)外接节点在水平荷载作用下的受力性能,以某钢桁腹-混凝土组合箱梁桥方案为背景,选取钢腹杆轴力最大节点设计、制作缩尺比为1∶3的钢桁腹-混凝土组合箱梁局部外接节点试件(由混凝土弦杆、方形钢腹杆、节点板组成,原混凝土板简化为混凝土弦杆)并开展静载试验,分析外接节点试件静载试验现象及破坏模式、荷载~位移曲线,以及混凝土弦杆、节点板和钢腹杆的应力分布规律,并基于有效宽度法及撕裂面法与最大强度准则提出外接节点极限承载力计算方法。结果表明:外接节点试件的破坏模式为节点板拉剪断裂失效,极限承载力为设计荷载的5.71倍,承载能力满足要求;混凝土弦杆压应力沿加载方向逐渐减小,沿竖直方向从上往下逐渐增大;节点板应力沿加载方向总体上先增后减,外露节点板是节点受力的关键构件;外接节点极限承载力由节点板和钢腹杆中较弱者控制,采用所提出的计算方法得到的外接节点极限承载力计算值与试验结果相差小于6%。

This study investigates the load bearing behaviors of the external joints of concrete box girders with steel truss webs(concrete top and bottom slabs and steel webs)under horizontal loads.Based on a design alternative of a double-track railway bridge,a 1∶3 scale model of the external joints with maximum axle forces was designed and prepared for static tests,which consisted of the concrete chords,square steel webs and gusset plates,and the original concrete slabs were simplified to be concrete chords.Multiple issues were analyzed,including the phenomena in the static test,failure mode,load-displacement curve as well as the stress distribution in the concrete chords,gusset plates and steel webs.Based on the effective width method,tearing surface method and the maximum strength criterion,the method to calculate the ultimate load bearing capacity of the external joint was proposed.It is shown that the fracture of gusset plates is the failure mode of the external joint specimen,the ultimate load bearing capacity is 5.71 times of the design loads,indicating that the load bearing capacity met the requirements.The stresses in the concrete chord gradually decreased along the loading direction,but increased downwards along the vertical direction.The stresses in the gusset plates changed from increase to decrease along the loading direction,and the exposed gusset plates are the key load bearing components.The weaker one,no matter it is the gusset plate or the steel web,dominates the ultimate load bearing capacity of the node.There is a 6% difference between the ultimate load bearing capacities calculated by the presented method and the test results.