连续钢箱梁抗火性能试验与演变机理

Experimental and Evolution Mechanism for Fire Resistance of Continuous Steel Box Girders

为研究火灾下具有板式橡胶支座支承条件的连续体系多室钢箱结构桥梁的高温响应,设计并制作了两榀两跨连续双室钢箱结构模型试验梁,对其开展了跨中区域与负弯矩区域的耐火试验。采用横向偏位加载实现弯扭耦合作用效应,制作了板式橡胶支座以研究火灾过程中支座性能的退化。通过试验获取了双室钢箱梁的截面温度分布特征、高温变形规律、钢梁屈曲模式以及裂缝开展过程,探析了火灾后钢材与橡胶支座的性能;然后建立了数值分析模型进行验证,结合模型计算剖析了其内力重分布规律与破坏过程,分析了负弯矩区功能失效路径,并开展了参数对比分析,揭示了连续钢箱梁抗火性能演变机理。研究结果表明:火灾下双室钢箱梁中腹板与边腹板的最大温差超过160℃,截面温度梯度分布受火灾强度的影响较大;单跨受火时受火跨持续下挠,而非受火跨先上拱后下挠,中支点受火时仅在末期出现位移激增,弯扭-高温耦合作用下双室钢箱梁出现随受火时间明显增长的横向扭转变形,破坏时截面两侧的挠度差值达到94 mm;连续钢箱梁在受火前期会发生剧烈的内力重分布,负弯矩区急剧扩大,中支座反力骤增至常温时的2倍以上;单跨受火时钢箱梁破坏状态表现出随着中支点附近的塑性扩展最终发展至受火跨的垮塌,而中支点受火时钢箱梁破坏状态则呈现出支点处钢梁的突然压溃,同一升温条件下中支点受火的钢箱梁破坏要远早于单跨受火,耐火极限缩短约40%;试验梁经历最高温933℃和825℃后,底板取样钢材的剩余强度分别约为67%和78%,钢梁的强度损失取决于其所经历的最高温度;橡胶支座具有良好的高温隔热性能,但外层橡胶在火灾下达到燃点后会导致橡胶燃烧碳化,进而使支座丧失承压能力,造成塌陷和支承功能失效,应对橡胶支座外部予以防火保护。该研究可为钢桥的抗火性能理论分析与结构性能提升方法提供指导依据。

To study the high-temperature response of continuous multichamber steel box bridge girders under rubber plate support conditions,two double-span continuous steel box bridge girders with twin chambers were designed and manufactured,and fire experiments were conducted under single-span fire and middle fulcrum fire conditions.The bending-torsion coupling effect was realized via transverse eccentric loading,and the plate rubber support was customized to determine the degradation of the bearing performance during fire exposure.The sectional temperature distribution,high-temperature deformation,buckling mode,and crack development of the bridge girders were obtained through the fire experiments,and the postfire properties of the steel and rubber supports were tested.Finally,a numerical model was established to verify the measured data,the internal force redistribution and failure processes were analyzed using model calculations,the failure process was analyzed as a function of the negative moment zone,and a parametric comparison analysis was conducted to determine the evolution mechanism of the fire resistance of continuous steel box girders.The results show that the temperature between the mid-web and side-web of steel box bridge girders exposed to fire exceeds 160℃,and the sectional temperature gradient distribution is significantly affected by the fire intensity.For single-span fire,the fire-exposed span deflects downwards,and the non-fire-exposed span first arches up before deflecting downwards;and for middle fulcrum fire,a sudden increase in the displacement is observed at the end of fire exposure.Moreover,the steel box bridge girder under the bending-torsion coupling effect exhibits evident transverse torsional deformation at high temperatures,where the difference in the deflection between the two sides of the section is 94 mm at the end.In the early stages of fire exposure,the internal force of the continuous steel box bridge girders is violently redistributed,and the region of negative bending moment expands sharply.Additionally,the reaction force of the middle support suddenly increases to more than twice that at room temperature.For single-span fire,plastic area expansion first occurs near the middle fulcrum followed by the eventual collapse of the fire-exposed span.In middle fulcrum fire,the compression buckling of the steel girder at the fulcrum leads to failure.Under the same heating mode,the failure of middle fulcrum fire occurs earlier than that of single-span fire,and the fire resistance limit reduces by approximately 40%.Moreover,the residual strength of steel on the bottom flange is approximately 67%and 78%at the maximum temperatures of 933℃and 825℃,respectively.Although the rubber supports have a good thermal insulation performance,fire protection should be provided outside the rubber supports because the outer rubber reaching the ignition point can cause burning and the carbonization of the rubber,which leads to a loss in the bearing capacity and depression of the support.Therefore,this study provides guidance for the theoretical analysis of fire resistance and structural performance improvement in steel bridges.