一种混凝土箱梁桥的可靠性评估方法

A reliability assessment method for concrete box-girder bridges

为评估混凝土箱梁桥正常运营期间的安全状态,基于桥梁健康监测数据与可靠度理论,以混凝土抗拉强度标准值为抗力,车辆荷载响应和竖向温度梯度荷载响应为荷载效应,建立正常使用极限状态方程.对于实桥监测的综合荷载应变响应,利用经验模态分解方法提取箱梁顶底板应变响应的温度趋势项,并对车辆荷载响应和竖向温度梯度响应进行概率密度函数拟合;对非正态分布的荷载效应当量正态化,计算最不利组合下箱梁跨中截面顶底板的失效概率.结果表明:监测的车辆荷载响应和竖向温度梯度荷载响应的概率密度函数均不满足正态分布,采用广义极值分布具有较好的拟合效果;箱梁顶底板的失效概率均小于1%,并在车辆荷载和竖向温度梯度的共同作用下,底板的失效概率显著升高.

In order to assess the working condition of concrete box-girder bridges during operation period,an assessment method was proposed combined the structural health monitoring data and the reliability theory. The normal use limit state equation was established by considering the resistance and load effects. In this equation,the concrete tensile strength standard value was taken as the resistance while and the vehicle load response and the vertical temperature gradient load response were taken as the load effects. For comprehensive strain responses acquiring from the bridge health monitoring system,a trend term extraction method based on empirical mode decomposition was proposed. Probability density distribution fitting of the vehicle load responses and the vertical temperature gradient load responses was conducted. Then,the equivalent normalization method was used for the load effect unsatisfying the normal distribution to calculating failure probability under the most unfavorable load combinations. Results show that the monitored vehicle load responses and the vertical temperature gradient load responses are not satisfy normal distribution,and the generalized extreme value distribution could get better fitting result. Moreover,the failure probabilities of the top plate and the bottom plate of the mid-span were less than 1%,and the risk of cracking of bottom plates significantly increases under the coupling of vehicle load and vertical temperature gradient load.