钢-混凝土组合连续弯箱梁抗火性能与设计方法

为研究提高钢-混凝土组合连续弯箱梁抗火性能的策略，选取某三跨钢-混凝土组合连续弯箱梁为研究对象，利用通用有限元软件ANSYS建立了其在火灾下的三维非线性两阶段分析模型；基于已有热-结构耦合分析方法，模型考虑了钢箱梁内空腔辐射传热过程和其上翼缘与混凝土板的接触边界条件；将模型得到的预测结果与试验数据进行了比较，验证了模型的可靠性；采用建立的模型在不同纵向受火位置、火灾强度和荷载水平作用下对钢-混凝土组合连续弯箱梁跨中挠度进行了参数敏感性分析，研究了其极限承载能力和刚度衰变规律；以火灾下跨中挠度为评估指标，提出了针对钢-混凝土组合连续弯箱梁的抗火设计方法。研究结果表明:在对称火和结构荷载作用下，钢-混凝土组合连续弯箱梁外边缘挠度大于内边缘挠度，且荷载越大，火灾越严重，这一效应越显著；在油罐车等过火面积较大的火灾作用下，刚度较极限承载能力衰退更快，与常温下的钢-混凝土组合连续弯箱梁极限承载能力和刚度相比，边跨受火16 min时极限承载能力和刚度分别降低至29%和14%，中跨受火28 min时极限承载能力和刚度分别降低至31%和22%；在钢-混凝土组合连续弯箱梁抗火设计中，应首先提高外侧钢箱梁在火灾下的刚度，增多和加宽外侧钢箱梁底板纵向加劲肋可使边跨受火20 min后内外侧钢箱梁跨中挠度差分别减小23%和30%，中跨受火32 min后内外侧钢箱梁跨中挠度差分别减小22%和27%。 

Fire resistance performance and design method of steel-concrete composite continuous curved box girders

As a strategy to improve the fire resistant performance of steel-concrete composite continuous curved box girders, a three-span steel-concrete composite continuous curved box girder was selected as a research object to establish a two-stage three-dimensional nonlinear analytical model under fire by employing the commonly used finite element software ANSYS. Based on the existing thermal-structural coupled analytical method, the developed model considered the radiation heat transfer in the cavity of steel box girder and the contact boundary conditions at the interface between the top flange of steel box girder and the concrete slab. The prediction results obtained by the model were compared with the experimental data to verify the model's reliability. The established model was used to conduct a parameter sensitivity of mid-span deflection of the steel-concrete composite continuous curved box girder under different longitudinal fire exposure positions, fire intensities, and load levels. The decay laws of ultimate bearing capacity and stiffness of the steel-concrete composite continuous curved box girder was studied. With the mid-span deflection under fire used as the evaluation indicator, a fire resistant design method of steel-concrete composite continuous curved box girders was proposed. Research results show that the deflection of the outer edge of steel-concrete composite continuous curved box girder is greater than that of the inner edge under the symmetrical fire and structural load, and this effect is more significant with greater loads and more severe fire. The stiffness decreases faster than the ultimate bearing capacity under a large burned area such as that resulting from a fuel tanker fire. Compared with the ultimate bearing capacity and stiffness of steel-concrete composite continuous curved box girder under normal temperature, the ultimate bearing capacity and stiffness reduce to 29% and 14%, respectively, when the side span is exposed to fire for 16 min, and they further reduce to 31% and 22%, respectively, when the middle-span is exposed to fire for 28 min. In the fire resistant design of steel-concrete composite continuous curved box girders, improving the stiffness of outer steel box girder under fire is necessary. Increasing and widening the longitudinal stiffeners of the bottom plate of outer steel box girder can reduce the mid-span deflection difference between the inner and outer steel box girders by 23% and 30%, respectively, when the side span is exposed to fire for 20 min, and by 22% and 27%, respectively, when the middle-span is exposed to fire for 32 min. 1 tab, 15 figs, 31 refs.