油罐车火灾下的钢桥高温屈曲失稳特性研究

Study on High-temperature Buckling Instability Characteristics of Steel Bridge under Oil Tanker Fire

为了探明钢桥火灾下的腹板和底板的临界屈曲应力变化规律,文章利用火灾动力学软件FDS建立钢桥热分析模型,将多项式拟合所确定的钢材热工参数函数赋予钢材板件,通过确定油罐车热释放率增长模型计算得到桥梁随时间变化的温度场。同时根据钢材板件屈曲理论计算得到火灾下桥梁腹板和底板随时间变化的临界屈曲应力,并采用有限元算法进行验证。结果表明:当油罐车燃烧17min时,腹板的临界屈曲应力将大幅度降低,小于此时由恒载、活载引起的腹板应力值,此时桥梁的跨中竖向位移小于规范设定的桥梁的容许位移值,桥梁火灾下将率先发生弯剪屈曲破坏而不是强度或位移破坏;钢结构桥梁桥下发生油罐车火灾后最佳抗火救援时间为火灾发生的15min内。

In order to find out the variation law of critical buckling stress of steel bridge web and bottom plate under the fire,this article uses the fire dynamics software FDS to establish the steel bridge thermal analysis model,assigns the steel thermal parameter function determined by polynomial fitting to the steel plate,and obtains the temperature field of the bridge changes with the time by determining the heat release rate model of the tanker.At the same time,according to the buckling theory of steel plate,it calculates and obtains the critical buckling stress of bridge web and bottom plate under the fire,which is then verified by finite element method.The results show that:when the tanker burns for17 min,the critical buckling stress of the web will be greatly reduced,which is less than the web stress value caused by dead load and live load.At this time,the mid-span vertical displacement of the bridge is smaller than the allowable displacement value of the bridge set by the specification,and,under the bridge fire,the shearing and buckling failure will occur firstly instead of the strength or displacement failure;the best fire rescue time for the steel-structure bridge after the oil tanker fire occurs is within15 min after the fire.