钢桁-混凝土组合结构桥梁耐火性能研究

Fire resistance of steel truss-concrete composite bridge girder

为研究钢桁-混凝土组合结构桥梁的耐火性能,选取公路交通简支下承式钢桁-混凝土组合结构桥梁为研究对象,建立了经试验验证的钢桁-混凝土组合结构桥梁三维实体非线性分析模型,研究其在桥下(下部)和桥面(上部)遭遇碳氢火灾时的温度空间分布特征,计算得到桥梁在不同受火长度和受火时间(下部受火)、不同受火位置(上部受火)影响下的挠度、承载能力的变化规律,给出不同火灾场景下的耐火极限。研究结果表明:受火长度和受火位置显著影响钢桁-混凝土组合结构桥梁的耐火性能;当桥下受火时,受火长度从L/20(L为计算跨径)增至L/4,钢桁-混凝土组合结构桥梁的耐火时间从大于60 min缩短至27 min,且挠度变形更为显著;当桥下20 m范围内受火45 min后,其承载力和结构刚度分别降低至常温下的72%和32%;桥面全车道和边车道受火均会使钢桁-混凝土组合结构桥梁先上挠后下挠,其耐火时间分别为25 min和31 min;边车道受火会使桥梁出现高温扭转变形;当全车道受火23 min后,其承载力和结构刚度分别降低至常温下的25%和10%;增大主桁高度可有效提高钢桁-混凝土组合结构桥梁的耐火性能,用箱形截面斜杆替换工字形截面斜杆则可使其耐火时间增加8.7%。

In order to investigate the fire resistance of steel truss-concrete composite bridge girders,a steel truss-concrete composite bridge girder with simple support conditions was chosen as the study subject.A 3D solid-structure nonlinear analysis model with fire-test validation was developed to study the spatial distribution properties of temperature when hydrocarbon fires are encountered on the lower and upper parts of the bridge.The fire resistance limits for different fire scenarios were determined by calculating the variation rules of structural deflection and bearing capacity of the bridge girder under different fire lengths,fire exposure times and fire locations.The results show that fire length and location significantly affect the fire resistance of steel truss-concrete composite bridge girder.When fire occurs under the bridge,the fire resistance time of steel truss-concrete composite bridge girder can be shortened from more than 60 minutes to 27 minutes as the fire exposure length increases from L/20(L is the calculated span)to L/4,and the deflection deformation is more significant.The bearing capacity and structural stiffness of steel truss-concrete composite bridge girder were reduced to 72%and 32%of normal temperature,respectively,after 45 minutes of fire in the lower 20 meters of bridge.When the fire occurs in entire lanes or side lane,the composite bridge girder presents a hogging and then drop,with fire resistance time of 25 minutes and 31 minutes,respectively.When there is a fire in a side lane,the bridge presents a high-temperature torsional deformation.After 23 minutes of entire lanes fire,the bearing capacity and structural stiffness were reduced to 25%and 10%of normal temperature,respectively.The fire resistance of steel truss-concrete composite bridge girder can be improved by increasing the height of main truss,and the fire resistance time can be increased by 8.7%by replacing the I-shaped diagonal web members with box diagonal web members.