某严寒地区连续梁桥腹板冻胀裂缝加固设计

Strengthening Design for Treating Frost Heave Induced Cracks in Webs of Continuous Girder Bridge in Cold and Harsh Climate

某严寒地区连续梁桥为(70+2×120+70)m预应力混凝土变截面连续箱梁桥,主梁悬臂施工4个节段后桥梁进入冬歇期,复工时在腹板悬臂前端面和侧面均出现了混凝土开裂现象,部分裂缝与竖向预应力孔道交叉,梁体还存在混凝土破损、空洞、钢筋外露锈蚀等质量缺陷。经分析,裂缝产生的主要原因是混凝土局部质量缺陷、竖向预应力体系密封性差,养生水、雨雪天气补水的冻胀及冻融循环作用。采用空压机向裂缝中灌注48 h(或以上)干燥空气以消除裂缝内残留水渍,对腹板粘贴内置式钢板,并在钢板外侧浇筑高性能混凝土进行加固。桥梁成桥荷载试验及运营监测结果表明加固达到了预期效果。

A continuous girder bridge in the area of cold and harsh climate is a prestressed concrete continuous box girder bridge with span arrangement of 70,2×120 and 70 m.After the cantilever installation of four segments of the main girder,the construction had to take a winter break.However,when the bridge construction was resumed,cracks were observed on the front-end and side surfaces of the concrete cantilever webs,some cracks even intersected with the ducts of vertical prestressing tendons,and various quality defects were found on the girder,such as concrete damage,voids and reinforcement exposure and corrosion.The cracks occurred due to the uneven quality of concrete,poor sealing property of the vertical prestressing system,and frost heave caused by moisture from concrete curing and rains and snows,and the effects of freezing-and-thawing cycles as well.Air compressors were employed to inject dry air into the cracks for 48 hours(or more)to remove the residual moisture in the cracks.The webs were strengthened by sticking inner steel plates,and high performance concrete was cast on the outer face of the steel plates to realize the remediation of the webs.The load tests for the completed bridge and the monitoring data in the operation period demonstrate that the strengthening achieves the expected effects.