基于改进损伤算法及MCMC车流模拟的 混凝土桥梁疲劳寿命预测

基于改进损伤算法及多车道精细车流模拟,提出一种新的混凝土桥梁疲劳寿命的预测方法.改进损伤算法将每一次循环造成的损伤计入S-N曲线,对疲劳荷载作用下材料的S-N曲线进行了修正,使得材料疲劳寿命预测结果更贴近真实状况.采用马氏链蒙特卡洛模拟法(Markov Chain Monte-Carlo,MCMC),考虑车流中相邻车型及车道的相关性,生成多车道精细车流.分别通过一组钢筋混凝土梁及一组预应力混凝土梁多级变幅疲劳试验对改进损伤算法的准确性进行了验证.介绍MCMC多车道随机车流模拟的具体流程,并提出基于改进损伤算法及多车道随机车流模拟的混凝土桥梁疲劳寿命预测方法.最后,以某高速公路实测交通流数据与一座跨径为20 m的简支T梁桥为例进行分析.结果表明:5组试件预测误差较常规损伤算法均有明显降低,除两根预应力混凝土梁预测误差较大(53％～56％)外,其余3组试件误差较小(小于8％),表明改进损伤算法可用来预测混凝土桥梁的疲劳寿命;实例分析中,简支T梁桥各主梁应力幅谱呈现多峰分布的特征,与车辆荷载分布特征相似,验证了模拟的合理性;根据改进损伤算法预测,当年交通量增长率(Average Annual Growth Rate,AAGR)为0时,该T梁桥的疲劳寿命为77.50年,不满足设计使用年限要求.AAGR为3％时,疲劳寿命为52.49年,较AAGR为0时下降32.27％.

Fatigue Life Prediction of Concrete Bridges Based on Improved Damage Algorithm and MCMC Traffic Flow Simulation

Based on the improved damage algorithm and multi-lane refined traffic flow simulation, a new method for predicting the fatigue life of concrete bridges was proposed, where the damage under each cyclic loading was introduced into the S-N curve in the improved damage algorithm. The S-N curve of materials under fatigue was modified in order that the predicted fatigue life of materials was closer to the real situation. The Markov chain Monte-Carlo simulation method (MCMC) was used to generate multi-lane fine traffic flow considering the correlation between adjacent models and traffic lanes. First, the accuracy of the improved damage algorithm was verified by the multistage variational fatigue tests of a group of reinforced concrete beams and a group of prestressed concrete beams. Then, the refined process of multi-lane random traffic flow simulation was introduced, and the fatigue life prediction process of concrete bridge based on improved damage algorithm and multi-lane stochastic traffic flow simulation was proposed. Finally, the traffic flow data measured on a highway and a simple supported T beam bridge with a span of 20m were used for example analysis. The results show that the prediction error of the five groups of specimens is significantly lower than that of the conventional damage algorithm. Except that the prediction error of two prestressed concrete beams is bigger (53%~56%), the prediction error of the other three groups of specimens is smaller (less than 8%), indicating that the improved damage algorithm can be used to predict the fatigue life of concrete bridges. In case of analysis, the stress spectrums appear the characteristic of multi-peak distribution, which is similar to the vehicle load distribution, illustrating the rationality of the simulation. According to the improved damage algorithm, when the average annual traffic rate (AAGR) is 0, the fatigue life of the bridge is 77.50 years, which didn''t meet the requirements of design service life. When AAGR is 3%, the fatigue life of the bridge is 52.49 years, which decreased by 32.27% compared with that when AAGR is 0.