斜拉扣挂悬臂浇筑拱桥扣索力与锚索力确定方法研究

Research on Methods to Calculate Forces of Forestay and Backstay Cables of Cable-Stayed Cantilever Casting System in Arch Bridge Construction

为解决钢筋混凝土拱桥拱圈悬臂浇筑施工过程中,由悬浇节段自重和挂篮重引起的部分拱圈截面拉应力与塔架偏位过大的问题,提出扣索力与锚索力确定方法。该方法基于应力叠加原理和影响矩阵确定扣索力,给出当拱圈截面拉应力不满足要求时的扣索拆除判定方法;提出通过锚索力修正系数主动调控扣索力与锚索力,使塔架产生与拱圈悬浇阶段数值接近、方向相反的偏位,给出能同时满足拱圈应力、塔架偏位和成拱线形要求的扣索力与锚索力的计算流程。以净跨径180 m的混凝土拱桥——毕节白甫河管桥为背景,开展扣索力、锚索力以及锚索力修正系数的计算,对扣索力、锚索力、拱圈应力、成拱线形和两岸塔架偏位的计算值和实测值进行对比验证。结果表明:利用所提方法得到的扣索力、锚索力与实际张拉力最大相差6.02%,该桥施工时,依次拆除5组扣索,使拱圈截面拉应力均满足设计要求;塔架偏位实测最大值为3.3 cm,满足小于最大容许偏位4.0 cm的要求;拱圈截面实测最大拉应力为1.74 MPa,满足小于1.8 MPa的拉应力设计要求,成拱线形与裸拱线形最大偏差为0.5 cm,拱圈线形良好,验证了所提方法的可行性。

In the construction of the arch of the reinforced concrete arch bridge,the self-weight of the cantilever-cast segments and weight of form travelers induce oversized tensile stresses in partial arch cross-section and offsets of the tie-up towers.This paper presents the methods to determine the forces of forestay and backstay cables,which is developed from the stress superimposition principle and influential matrix to determine forestay cable forces,and derive the method to judge the timing to dismantle forestay cables when the stresses in the arch cross-section do not meet the requirements.It is suggested to utilize the correction coefficients of backstay cable forces to actively adjust the forces of the forestay and backstay cable forces,to allow the tie-up tower to generate the backstay cable forces that approximate the data in the cantilever casting of the arch,but in the opposite direction.And a calculation procedure for the forestay and backstay cable forces that could simultaneously meet the requirements of arch stresses,tie-up tower offset and alignment of the completed arch is proposed.The presented methods have been applied to an aqueduct crossing Baifuhe River,a concrete arch bridge spanning 180 m.The calculated and measured values of the forestay cable forces,backstay cable forces,stresses in arch,completed arch alignment and the offsets of the two tie-up towers were compared.It is shown that the maximum tension difference between the forces of forestay and backstay cables calculated by the presented methods and the actual tensioning forces is 6.02%.During construction,five pairs of forestay cables can be dismantled in sequence to make the tensile stresses in the arch cross-section meet the design requirements.The measured maximum offset of the tie-up tower is 3.3 cm,smaller than the maximum allowable limit offset of 4.0 cm.The measured maximum tensile stress in the arch cross-section is 1.74 MPa,below the design value of 1.8 MPa.The bias between the alignment of the completed arch and bare arch alignment is 0.5 cm,indicating a sound arch alignment and proving that the presented methods are applicable.