火灾下大跨度钢桁架拱桥结构性能分析

Analysis of structural performance of long-span steel trussed arch bridge exposed to fire

摘要:

为研究汽车火灾对大跨度钢桁架拱桥结构受力性能的影响,以主跨为240 m的某下承式钢桁架拱桥为研究对象进行受火分析计算. 首先利用火灾模拟软件FDS对两种典型火灾场景进行数值模拟获得火灾温度场分布,然后通过有限元瞬态热分析确定火灾区域构件的温度分布,再通过ABAQUS热-结构耦合分析桥梁在不同火灾场景下结构性能的变化. 结果表明:钢桁架拱肋在油罐车火灾作用下受火构件的最高温度达540 ℃；主要传力构件在温度为430 ℃时屈服,达到承载能力极限状态,热膨胀效应与内力重分布导致附近构件的应力增幅达60~180 MPa；桥面竖向位移变化最大为115 mm,最大横向高差为108 mm. 油罐车火灾主要对火源附近3根吊索的温度场产生影响,受火吊索索力减小使得桥面下挠33 mm,主梁应力增大35 MPa.

Abstract:

To study the effect of vehicle fire on the structural performance of long-span steel trussed arch bridge, a down-supported steel trussed arch bridge with main span of 240 m was taken as the research object for analysis and calculation. First, fire dynamic simulation (FDS) was utilized to simulate the fire temperature field distribution of two typical fire scenarios. Then, the temperature distribution inside the steel member was obtained by finite element instantaneous heat analysis. Finally, the ABAQUS thermal-structural coupling was used to analyze the structural performance variation of the bridge in different fire scenarios. Results show that the highest temperature of the steel arch rib members under the effect of tanker fire was up to 540 ℃. The main load transmitting member yielded at the temperature of 430 ℃, which reached the ultimate limit state, and thermal expansion and internal force redistribution led to the stress increase of the member in the fire area up to 60-180 MPa. The maximum variation of the vertical displacement of the bridge deck was 115 mm, and the maximum lateral height difference of the deck was 108 mm. The oil tanker fire mainly affected the temperature field of the three hanger rods near the fire area. Due to the reduction of the hanger rod force in the fire, the down deflection of the bridge deck was 33 mm and the stress of the main girder increased by 35 MPa.