大跨度连续刚构桥腹板开裂原因分析

Analysis of Web Cracking of Long-span Continuous Rigid Frame Bridge

建立预应力混凝土连续刚构桥有限元模型,分析箱梁横向框架效应、竖向预应力效应、腹板下弯束作用、主拉应力限值、车辆超载、温度梯度等因素对腹板裂缝的影响。结果表明,箱梁横向框架效应对腹板主拉应力影响较大,其单项引起的腹板主拉应力超过0.5 MPa,该值可使腹板某些区域的压应力减弱甚至完全被抵消,进而引起腹板出现斜裂缝;竖向预应力钢束提供的箱梁腹板混凝土压应力储备在2~4 MPa,且随着竖向预应力损失增大,所引起的主拉应力持续显著增大,导致腹板开裂;腹板下弯束在主梁根部附近对主梁的压应力储备贡献最大,从主梁根部至两边跨中标准节段,主梁的压应力储备随着腹板钢束下弯角度的快速减小而逐渐减小;成桥阶段锚固点尽量下移可以显著提高桥梁的压应力储备,达到充分发挥下弯钢束抗剪,抑制腹板斜裂缝发展的作用;主拉应力与车辆超载量基本呈线性关系,超载会导致箱梁结构处于高应力状态,产生开裂等病害;不同温度梯度模式计算出的应力差异较大。

The finite element model of prestressed concrete continuous rigid frame bridge was established to analyze the influence of transverse frame effect of box girder,vertical prestressed effect,bent-down tendons of web,principal tensile stress limit,vehicle overload,temperature gradient and other factors on web cracks.The results show that the transverse frame effect of the box girder has a great influence on the principal tensile stress of the web.The principal tensile stress of the web caused by a single item is more than 0.5 MPa,which can weaken or even completely offset the compressive stress in some areas of the web,and then cause diagonal cracks in the web.The compressive stress of the box girder web concrete provided by the vertical prestressed steel tendon is stored in 2~4 MPa,and the principal tensile stress caused by the loss of vertical prestress continues to increase significantly,eventually leading to web cracking.The bent-down tendons of the web contributes the most to the compressive stress reserve of the main girder near the root of the main girder.From the root of the main girder to the standard midspan section on both side spans,the compressive stress reserve of the main girder decreases gradually with the rapid reduction of the bent-down angle of web tendons.At the completion stage,the anchorage point should be moved down as far as possible to significantly improve the compressive stress reserve of the bridge,so as to give full play to the shear resistance of bent-down tendons and inhibit the development of diagonal cracks in the web.The principal tensile stress is basically linear with the vehicle overload.Overload will cause the box girder structure to be in a high stress state,causing cracks and other diseases.The stress calculated by different temperature gradient models is quite different.