分级车辆火灾下吊索系统的抗火性能计算方法  

Calculation Method for Fire Resistance of Hanger Systems Under Vehicle Fires

作　　者：刘志 李国强[1,2] LIU Zhi;LI Guo-qiang(School of Civil Engineering,Tongji University,Shanghai 200092,China;State Key Laboratory for Disaster Reduction in Civil Engineering,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学土木工程学院,上海200092 [2]同济大学土木工程防灾减灾全国重点实验室,上海200092

出　　处：《中国公路学报》2024年第9期1-16,共16页China Journal of Highway and Transport

基　　金：国家自然科学基金项目(52308521)。

摘　　要：为计算车辆火灾下悬索桥吊索系统的抗火性能,将桥梁车辆火灾分为五级:第一、二级为乘用车火灾,第三、四级为货车火灾,第五级为油罐车火灾,采用不同的最大热释放速率和最大燃烧时长对其进行表征。根据已有的车辆火灾试验,验证该分级方法的合理性,并结合车辆火灾事故,建立第三、四、五级车辆火灾火源的几何特征。采用圆柱火焰辐射体模型,计算乘用车火灾的空间辐射热流密度,并得到3例足尺汽车火灾试验的验证;采用棱柱火焰辐射体模型,计算货车火灾的空间辐射热流密度;采用经液化天然气池火试验验证的计算流体动力学方法,计算有横风时油罐车火灾下吊索表面的空间热流密度包络;推导了吊索截面在辐射热流密度边界条件下的增量法升温计算公式,并得到了有限元模型的验证。根据已有的高强钢丝高温力学性能试验,基于吊索在火灾下的承载能力极限状态,提出了吊索临界温度与吊索设计安全系数的函数关系。最后,整合上述研究结果,提出了分级车辆火灾下吊索系统抗火性能的五步计算方法,可为悬索桥吊索系统的抗火安全评定与设计提供参考。To evaluate the fire resistance of hanger systems in suspension bridges,vehicle fires are classified into five levels.Levels 1 and 2 represent passenger vehicle fires,levels 3 and 4 correspond to truck fires,and level 5 represents tanker fires.These vehicle fires are characterized by distinct maximum heat release rates and burning durations.The proposed hierarchy was validated using existing vehicle fire experiments.Geometric features of flames are established for Levels 3,4,and 5 vehicle fires based on previous vehicle fire incidents.For passenger vehicle fires,a cylindrical flame radiation model was employed to compute spatial radiative heat flux,validated through three full-scale car fire tests.In the case of truck fires,a prismatic flame radiation model was used to calculate spatial radiative heat flux.For tanker fires with crosswinds,a computational fluid dynamics method validated by a liquefied natural gas trench fire test was employed to calculate the heat flux envelope on the hanger surface.An incremental temperature calculation formula for hanger cross-sections with radiative heat flux boundary conditions was derived,and validation was performed using finite element models.Using mechanical property tests of high-strength steel wires at high temperatures,a quantitative relationship between critical temperature and design safety factor of hangers is developed based on the ultimate load-carrying capacity at high temperatures.Finally,integrating the above outcomes,a five-step theoretical framework is proposed to evaluate the fire resistance of hanger systems under graded vehicle fires.This algorithm can serve as a reference for the assessment and fire-resistance design of hanger systems in suspension bridges.

关 键 词：桥梁工程 车辆火灾 理论分析 吊索系统 抗火性能 悬索桥 

分 类 号：U442.5[建筑科学—桥梁与隧道工程]