油罐车火灾下大跨径双层钢桁梁悬索桥高温力学性能

为了确定大跨径双层钢桁梁公路悬索桥油罐车燃烧下的损伤破坏情况,以武汉杨泗港长江大桥为背景,利用火灾动力学软件FDS模拟桥梁上7种不同火灾燃烧场景,以此确定出桥梁最不利油罐车火灾热释放率函数增长模型及规模。建立双层公路悬索桥三维空间热分析模型,通过热分析确定油罐车在桥梁不同部位发生火灾时其三维空间瞬态温度场分布规律。通过热-结构耦合分析,掌握双层钢桁梁悬索桥吊索、加劲梁、桁架杆高温力学性能时变特征。结果表明:恒载+活载工况作用下,一辆油罐车在桥梁主跨跨中上层最外车道发生火灾36 min时,吊索温度达到900 ℃以上,吊索应力增大到362.4 MPa,达到高温下抗拉强度,此时吊索发生断裂破坏,吊索的破坏主要是由于高温下的抗拉强度退化造成,此场景下抗火救援的最佳时间在16 min内; 一辆油罐车在桥梁主跨跨中下层非机动车道发生火灾43 min时,上层钢桁梁横梁腹板的临界屈曲应力系数降低到了1以下,上层钢桁梁火灾下率先会发生局部屈曲失稳而不是强度或位移破坏,此时抗火救援的最佳时间在20 min内。

High Temperature Mechanical Properties of Long-span Double-deck Steel Truss Beam Suspension Bridge Under Tanker Fire

In order to acquire the failure characteristics of long-span double-deck steel truss girder suspension bridge under tanker fire, Yangsigang Yangtze River Bridge in Wuhan was taken as an example, and the fire dynamics software FDS was used to simulate seven different fire burning scenarios on the bridge, so as to determine the most unfavorable growth model and scale of the bridge tanker fire heat release rate function. A three-dimensional spatial thermal analysis model of double-deck highway suspension bridge was established. The three-dimensional transient temperature field distribution laws when tanker fire occurred in different parts of bridge were confirmed though thermal analysis. Through thermal-structure coupling analysis, the time-varying characteristics of high temperature mechanical properties of suspension cables, stiffening beams and truss bars of double-deck steel truss suspension bridge were mastered. The results show that when a tanker fire happens in the upper outer lane of midspan of the main span under dead load and live load with 36 min, the temperature of sling reaches 900 ℃, and sling stress increases to 362.4 MPa which is equal to sling tensile strength at high temperature. At this time, the sling breaks, and the damage of the sling is mainly due to the degradation of tensile strength at high temperature. The best time for fire rescue in this scenario is within 16 min. When a tanker fire happens in the lower non-motorized lane of midspan of the main span with 43 min, the critical buckling stress coefficient of the upper beam web was reduces below 1, and the failure characteristics of the bridge was local buckling instability rather than strength or displacement failure. The best fire rescue time should be within 20 min under this scenario.