基于监测数据的钢箱梁U肋细节疲劳可靠性分析

FATIGUE RELIABILITY ANALYSIS OF U-RIB DETAIL OF STEEL BOX GIRDER BASED ON MONITORING DATA

针对某悬索桥钢箱梁疲劳开裂严重,基于WIM动态称重系统采集的数据,对该桥通行车辆的车型、轴距、轴重、总重、是否超载进行了统计,明确了该桥交通荷载特征及各车道随机车流差异性,依据实桥动应变监测数据,运用雨流计数法及Palmgren-Miner线性损伤累积理论,获得了运营状态下各车道的疲劳应力谱,基于均匀设计-径向基神经网络-重要蒙特卡罗法(UD-RBF-IMC)相结合的算法,运用线弹性断裂力学对U肋对接焊缝疲劳可靠性进行了评估,研究了交通量及轴重增长对疲劳可靠度的影响规律。研究结果表明:该桥疲劳车型可简化为V2~V10共9类,左、右幅V2车型的总重均为单峰偏态分布,超载率不到4%,V3~V10车型的总重均为多峰分布,超载率大于30%,最高达69%;重车道V2~V10车型的比例明显高于其他车道;温度日变化对疲劳应力谱的影响较小,采样频率对应力谱的影响较为显著,不宜小于50 Hz;结合UD、RBF、IMC算法各自的优点,有效提高了基于监测数据的钢箱梁细节疲劳可靠度指标的求解精度和效率;轴重增长系数对疲劳可靠度的影响明显大于交通量增长系数,在运营期间除控制交通量外,还需重点控制重车比例和超载率;当交通量增长系数为3%,轴重增长系数为0.6%时,1#测点疲劳寿命仅为74年;超车道重载卡车数量较少,高水平应力循环较少,疲劳寿命较长,而快车道和重车道重载卡车较多,高水平应力循环较多,存在疲劳开裂风险,需重点关注。

Aimed at the problem that there is serious fatigue cracking in the steel box girder of a suspension bridge,the vehicle type,wheelbase,axle load,total weight and overload of the bridge are statistically analyzed,and the traffic load characteristics of the bridge and the difference of random traffic flow in each lane are clarified by the base of the data collected by a WIM dynamic weighing system.According to the dynamic strain monitoring data of a real bridge,the fatigue stress spectrum of each lane under operating condition was obtained by using the rain-flow counting method and the Palmgren-Miner linear damage accumulation theory.Based on the UD-RBF-IMC algorithm,the fatigue reliability of U-rib butt weld was evaluated by linear elasticfracture mechanics.The influence of traffic volume and the shaft weight on fatigue reliability were studied.Theresult show that:the type of a fatigue vehicle can be simplified to V2-V10,a total of 9 categories,the total weightsof V2 vehicles are a unimodal skewed distribution,overload rate of less than 4%,the total weights of V3-V10vehicles are multi-peak distribution,overload rate greater than 30%,up to 69%.The proportion of V2-V10vehicles of a heavy lane is obviously higher than that of other lanes.The daily variation of temperature has littleeffect on the fatigue stress spectrum,and the influence of sampling frequency on the stress spectrum is significant,which should not be less than 50 Hz.Combining the respective advantages of UD,RBF and IMC,the accuracyand efficiency of the fatigue reliability index of steel box girders based on monitoring data are effectivelyimproved.The effect of axle weight growth coefficients on fatigue reliability is obviously greater than that oftraffic volume growth.In addition to controlling the traffic volume during operation,it is also necessary to focuson controlling the proportion of heavy vehicles and overloading rate.When the growth coefficient of trafficvolume is 3%and the growth coefficient of axle load is 0.6%,the fatigue life of measuring point 1#is only 74years.The number of overloaded heavy-duty trucks of passing lane is less,the high-level stress cycles are less,and the fatigue life is longer,while the number of heavy-haul trucks of a fast lane and a heavy lane is more,thehigh-level stress cycles are more,there is a risk of fatigue cracking,which should be paid more attention to.