文档介绍：预应力连续梁底板混凝土开裂事故原因分析及处理
摘要:通过对某桥主桥125m跨连续箱梁跨中底板混凝土开裂的经过、原因分析,以及修复加固方案设计和实施的资料搜集,总结质量缺陷原因,用以指导后续类似桥梁在图纸审核、现场施工。该桥竣工后经静载试验表明:实测应变值和挠度值均小于计算值,结构受力状态良好,说明梁体的修复加固满足使用要求。
关键词:连续梁;开裂;分析;加固
Abstract: through the analysis of the causes of, on a bridge of 125m span continuous box girder mid-span bottom slab crack of concrete, and the repair and reinforcement design and implementation of data collection, summary of the causes of quality defects, to guide the subsequent similar bridges in the drawing review, construction. After pletion of the bridge by static load tests show that: the measured strain and deflection values were less than the calculated value, force structure is in good condition, the instructions to repair the beam reinforcement to meet the use : continuous beam; crack; analysis; reinforcement中图分类号::A 文章编号:2095-2104(2013)
1工程概况
新建环城高速公路一座特大型桥梁,跨越Ⅲ级通航水道主河槽。主桥上部结构设计为(75+125+75)m变截面预应力混凝土连续箱梁,左右幅分离,按双向四车道标准设计,采用挂篮悬浇施工。,设计荷载:汽车超-20,挂车-120。
2事故经过
该大桥合龙顺序为先边跨后中跨,中跨合龙段施工后,混凝土龄期达到11d,(设计混凝土标号C50),开始张拉中跨底板预应力钢束,张拉顺序为先长后短,对称张拉。原设计跨中合龙段纵向底板钢束共37束,(标准强度Rb=1860MPa)和OVM大吨位群锚,每束锚下控制张拉力2340KN,见图1:

图1主桥中跨底板预应力束布置图
当张拉到第31束时,听到梁体有异常响声,经检查后,发现用于浇筑合龙段的吊架底模纵梁和横梁变形,合龙段(20#块)及两侧的19#、18#块箱梁底板呈弧面下挠,底板混凝土沿纵向严重开裂,底板钢束以下的钢筋混凝土剥离,,裂缝间距20~40cm不等,裂缝影响到18#断面,总长度约18m。当时张拉工作立即停止,考虑安全和减少跨中