火灾环境下钢结构力学响应行为研究回溯与前瞻

Research progress and new problems on the mechanical response of steelmade structures in the fire environment

火灾环境下高温对结构钢材的力学性能具有显著的不利影响。通常钢材在200~400℃的温度下力学性能开始下降,在800℃以上几乎丧失所有的强度。火灾环境下的钢结构力学响应行为是钢结构抗火设计的前提。为了展示火灾环境下钢结构的力学响应研究的清晰脉络,首先综述了火灾环境工况加载、钢结构升温规律的研究文献,然后从钢的耐火性能分析开始,评述了钢结构形式对耐火性能的影响和热作用下的结构变形研究。研究表明:若采用ISO 834标准升温曲线作为热加载方式,钢结构的升温规律和力学响应行为与真实火灾场景下相比差异显著,在标准火下钢的抗火时间更长;钢结构在火灾环境下的热应变随温度升高而增大,最终导致屈曲和过度挠度;当温度超过400℃时,高温蠕变会加速结构的失效;试验和数值模拟方法能很好地预测钢结构在真实火灾环境下的温升规律;较为真实地表征钢结构的不均匀力学响应行为,首先需要加载真实的火灾工况,同时要充分考虑钢结构形式,并耦合运用工程热物理、力学相关工具和方法;钢附着可燃材料燃烧的热反馈及相应的力学响应行为是钢结构抗火研究的新问题,针对该问题需要建立科学的热-力耦合工程定量测试方法。

The paper is inclined to clarify and determine the clear context of the mechanical response of steel structures in the fire condition through primary revision of the literatures on fire load,heating and mechanical behaviors of steels.The high temperature of the fires has a significant adverse effect on the mechanical properties of the structural steel with mechanical response behaviors under the fire conditions being the prerequisite for the fire resistance design.However,steels usually begin to deteriorate at the temperature between 200-400℃and almost all of its strength would be getting lost above 800℃.And,then,beginning with the analysis of the fire resistance of steels,we have made a careful revision of the effects of the steel structure forms on the fire resistance and its structural deformation under high temperatures.Thus,the research results we have gained show that the heating regularity and its mechanical response behavior turn out to be significantly different from those in the authentic fire scenarios if the ISO 834 standard heating curve can be used for such high standard temperature heating load due to the longer fire resistance.The thermal strains of the steel structures under the fire conditions may increase with the temperature,eventually leading to buckling and excessive deflection.On the contrary,the failure of the steel structures can also be accelerated due to the high-temperature creep when and if the temperature exceeds 400℃.And,thus,the experimental and numerical simulation methods can well be used to forecast that the temperature rise of the steel structures should be arrived at as in the real fire scenarios.To accurately characterize the non-uniform mechanical behavior of the steel structures,it is also necessary to take into full account the influential effects of the steel structure forms under the authentic fire conditions to couple with the engineering thermophysics and mechanics tools.For,in so doing,the heat feedback of the combustible materials attached to the structural steels and corresponding mechanical response behavior of the steels should be the new issues in the study of fire resistance of steel structures,and research into such issues ought to demand the establishment of a scientific thermo-mechanical quantitative testing method.