火灾爆炸耦合作用下悬索桥动力响应分析

Dynamic Response Analysis of Suspension Bridge Under Coupled Effects of Fire and Explosion

摘要

为研究悬索桥在火灾爆炸耦合作用下的破坏倒塌机理,利用显式动力分析软件ANSYS/LS-DYNA平台,建立了包含钢桥塔等主要构件的悬索桥精细化三维有限元模型．首先,利用火灾分析软件FDS建立悬索桥上油罐车火灾热分析模型,得到温度随空间的变化特征．其次,利用LS-DYNA有限元软件进行热-结构耦合分析,研究悬索桥桥塔附近在火灾单独作用下的温度分布特征和结构响应．再次,采用对材料属性进行相应折减的方式来模拟高温对材料强度的折减,探究了悬索桥桥塔附近火灾爆炸耦合作用下关键构件的损伤及其倒塌过程．最后,对悬索桥跨中火灾作用下的倒塌过程展开研究．结果表明：桥塔受火面的温度受火灾影响最大,桥塔温度沿高度方向存在明显的温度梯度,钢箱梁因桥面铺装的作用,温度升高不明显；桥塔及钢箱梁因热膨胀效应引起的应力增长较大,不可忽略；桥塔因受火面热膨胀效应影响产生偏离受火面的位移；随着火灾持续时间延长或爆炸冲击强度增大,桥塔结构的损伤程度呈现显著加剧,在火灾初期损伤大小主要由爆炸当量控制；桥塔附近损伤是高温及爆炸共同作用的结果,单一作用对其影响较小；跨中仅在火灾作用的工况下发生倒塌．

Abstract

To investigate the failure and collapse mechanisms of suspension bridges under the coupled effects of fire and explosion, a detailed three-dimensional finite element model of a suspension bridge including key components such as steel pylons was developed using the explicit dynamic analysis software ANSYS/LS-DYNA. First, the fire analysis software FDS was employed to establish a thermal analysis model of a tanker truck fire on the suspension bridge, thus obtaining the spatial variation characteristics of temperature. Second, the LS-DYNA finite element software was used to conduct a thermal-structural coupling analysis, so as to study the temperature distribution and structural response near the pylon under fire alone. Third, the reduction in material strength due to high temperatures was simulated by appropriately degrading material properties, and the damage to key components and the collapse process near the pylon under the combined effects of fire and explosion were explored. Finally, the collapse process of the suspension bridge under fire at the mid-span was analyzed. Results indicate that the temperature on the fire-exposed surface of the pylon is most significantly affected by fire, with a notable temperature gradient along the height of the pylon. Due to the influence of the bridge deck pavement, the temperature rise in the steel box girder is not significant. The stress increase in the pylon and steel box girder caused by thermal expansion effects is considerable and cannot be ignored. The pylon exhibits displacement away from the fire-exposed surface due to thermal expansion effects. As the duration of fire or the intensity of the explosion impact increases, the damage to the pylon structure significantly worsens. At the early stage of fire, the extent of damage is primarily controlled by the explosion equivalent. The damage near the pylon results from the combined effects of high temperature and explosion, with each factor alone having a minor impact. The collapse at the mid-span only occurs under the scenario of fire alone.

关键词

火灾 / 爆炸 / 悬索桥 / 有限元分析 / 连续倒塌

Key words

fire / explosion / suspension bridge / finite element analysis / progressive collapse

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基金资助

国家自然科学基金资助项目(51238007)

国家自然科学基金资助项目(51178310)