非对称预应力混凝土箱梁水化热温度及应变监测与分析

Monitoring and Analysis of Hydration Heat Temperature and Strain of Asymmetric Prestressed Concrete Box Girder

为探讨通过预应力钢束分阶段张拉抑制连续箱梁早期裂缝的可行性,对余姚—慈溪高速公路一联四跨非对称预应力混凝土连续箱梁二次浇筑过程中混凝土早期水化热和应变进行了连续监测,分析顶腹板温度和应变的变化及其分布规律。结果表明:顶腹板交界处与箱室顶板中心的最大温差出现时间滞后于顶腹板交界处与腹板顶部,虽两者最大温差相差不大,但后者温差达到峰值时二次浇筑混凝土已终凝约20 h;在首次浇筑的腹板混凝土和模板的约束下,由顶腹板交界处与箱室顶板中心温差产生的温度应力容易造成二次浇筑混凝土早期开裂;对连续现浇箱梁预应力钢束分阶段张拉,可减小二次浇筑后顶腹板交界处混凝土早期拉应变,有效降低箱梁顶板开裂的风险。

In order to explore the feasibility of restraining the early cracks of continuous box girder by tensioning the prestressed steel tendons in stages,the early hydration heat and strain during the secondary concreting of a four spans asymmetrical prestressed concrete continuous box girder on Yuyao-Cixi expressway was continuous monitored,and the changes and distribution of the temperature and strain of the roof and web were analyzed.The results show that the maximum temperature difference between the junction of roof and web and the center of box girder roof lags behind that the junction of roof and web and the top of web.Although there is little difference between the two,when the temperature difference of the latter reaches its peak,the secondary concreting has finally setting for about 20 h.Under the constraints of the first concreting web concrete and formwork,the temperature stress caused by the temperature difference between the junction of roof and web and the center of the box girder roof is easy to cause early cracking of the second concreting concrete.The early tensile strain of the concrete at the junction of roof and web can be reduced by tensioning the prestressed steel tendons of the continuous cast-in-place box girder in stages.It can effectively reduce the cracking risk of box girder roof.