基于疲劳寿命的钢筋混凝土桥梁限载取值分析方法

Vehicle Weight Limit Analysis Method for Reinforced Concrete Bridges Based on Fatigue Life

为了确定钢筋混凝土桥梁限载的合理取值,针对钢筋混凝土桥梁的疲劳性能,考虑随机车流参数、超限车违规率等因素的影响,进行了基于疲劳寿命的桥梁限载取值分析方法研究,提出了一种基于S-N曲线和Palmgren-Miner线性累积损伤理论的桥梁限载取值分析方法。首先基于交通荷载资料和蒙特卡罗法进行随机车流模拟,根据桥梁限载试算值和超限车违规率剔除超限车得到修正的模拟随机车流;然后通过雨流计数法得到应力幅谱,根据S-N曲线和疲劳损伤准则计算桥梁疲劳寿命;最后取能使桥梁疲劳寿命达到期望值的限载试算值作为桥梁限载值。以某地区的交通荷载资料及跨径为20m的简支T梁桥为例,确定了在不同日均交通量和超限车违规率下能使桥梁疲劳寿命达到期望使用年限的桥梁限载值。研究结果表明:日均交通量和超限车违规率均显著影响桥梁的疲劳寿命及桥梁限载取值,日均交通量越大,桥梁的疲劳寿命越短;当日均交通量小于6 000veh时,在不同的桥梁限载值下桥梁的疲劳寿命均大于期望使用年限,当日均交通量大于8 000veh时,桥梁的疲劳寿命仅在特定桥梁限载值下才能达到期望使用年限;超限车违规率越大,通过调整桥梁限载值来提高桥梁疲劳寿命的效果越不明显,当超限车违规率较小时,桥梁的疲劳寿命随限载试算值的减小而大幅增长,当超限车违规率较大时,桥梁的疲劳寿命随桥梁限载试算值的减小,增幅并不明显。

To determine the reasonable weight limit for reinforced concrete bridges, a vehicle weight limit analysis method based on fatigue life was conducted with the consideration of the effects of the random traffic flow parameters and overload violation rate, in view of fatigue performance of reinforced concrete bridges. The vehicle weight limit analysis method for reinforced concrete bridges based on the S-N curve and Palmgren-Miner linear cumulative damage rule was proposed. The random traffic flow was firstly simulated according to the collected traffic data and Monte Carlo method, and then calibrated using the initial value of weight limit and overload violation rates to exclude overweight trucks. The traffic-induced stress spectrum of the bridge was obtained by rain flow counting algorithm and fatigue life was calculated based on the S-N curve and Palmgren-Miner rule. The procedure was iterated until the value of weight limit was able to achieve the desired fatigue life of the bridge and thus deemed it as the final reasonable value. Taken the traffic data of a specific area and a typical simply-supported T-beam bridge with span length of 20 m as examples, reasonable weight limits with fatigue life of bridges reaching expected working life were determined for different average daily traffic volumes （ADTVs） and different violation rates. The results show that both the ADTV and the overload violation rate can significantly affect the fatigue life of the bridge components and the vehicle weight limit on bridge. The higher the ADTV is, the shorter the bridge fatigue life can be. Specifically, the desired bridge fatigue life is much longer than expected working life under different weight limits when the ADTV is less than 6 000. However, the expected working life can only be achieved under certain weight limits when the ADTV is larger than 8 000. The higher the violation rate is, the less effective the method of setting vehicle weight limit is to prolong the bridge fatigue life. With small violation rate, the bridge fatigue life increases rapidly with the decrease of the initial weight limit value. However, with large violation rate, limited increment of bridge fatigue life can be achieved with the decrease of the initial weight limit value.