连续刚构桥施工过程中腹板裂缝检测与研究

Detection and Analysis of Web Cracks in Construction of Continuous Rigid Frame Bridge

研究目的:针对某大跨预应力混凝土连续刚构桥在施工过程中腹板开裂的问题,对该桥主桥腹板所有裂缝进行全面检查,完成可查裂缝宽度、深度的检测。通过归纳总结裂缝的分布特征,利用有限元分析软件ANSYS建立开裂混凝土节段的空间模型,结合腹板开裂相关理论,分析腹板开裂的原因,探究裂缝分布规律。研究结论:(1)腹板两侧的裂缝基本对称于箱梁纵轴线,较多出现在腹板内侧,与腹板下弯束的布置位置、方向符合程度较高;(2)有限元分析结果表明,腹板下弯束及其锚固点周围的部分区域主拉应力超过混凝土抗拉强度设计值,且该区域基本沿预应力束分布;(3)该腹板裂缝属于主拉应力裂缝,过大拉应力主要来源于预应力束径向力、箱梁空间效应产生的次拉力以及锚固应力扰动区的横向拉应力;(4)设计者应重视箱梁横向应力和空间效应,必要时对复杂受力区域进行精细的局部分析,以保证主拉应力不超过限值;(5)本研究成果可为预应力混凝土连续刚构桥的相关设计及施工提供参考借鉴。

Research purposes: Due to the problem of web cracking during the construction of a large span prestressed concrete continuous rigid frame bridge,all the cracks on the webs of the main bridge were completely inspected and the detection of the width and depth of the conditional cracks was accomplished. The distribution characteristics of cracks was summarized,a spatial model of the cracked concrete segment was established by the finite element software ANSYS and the theory of web cracking was referred to for the purpose of analyzing the causes of web cracking,exploring the distribution law of cracks.Research conclusions:( 1) The cracks on both sides of the web are basically symmetrical to the longitudinal axis of the box girder,and more appear on the inner side of the web,which is more consistent with the arrangement position and direction of the bent-down prestressed tendon in the web;( 2) The result of finite element analysis shows that the principal tensile stress of the zone near the bent-down tendon and its anchorage exceeds the design value of concrete tensile strength,and the zone is basically distributed along the prestressed tendon;( 3) It is determined that the crack is caused by the excessive principal tensile stress which is composited with radial force from prestressed tendon,secondary tension generated by box girder space effect and transverse tensile stress of anchorage stress disturbance region;( 4) The designer should pay attention to the lateral stress and space effect of the box girder,and perform detailed local analysis on the complex force area if necessary to ensure that the principal tensile stress does not exceed the limit;( 5) The research results can provide reference for the design and construction of prestressed concrete continuous rigid frame bridges.