【作者】 王勇；

【导师】 董毓利；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2013， 博士

【摘要】 由于钢筋混凝土材料的众多优点，其被广泛应用于各类建筑结构工程中。然而，火灾易造成材料性能恶化，严重时结构出现倒塌，所以近年来结构或构件的抗火性能研究受到国内外学者的广泛关注。最近，为了增强对整体结构中构件火灾行为的理解，本课题组开展了钢框架结构中单一区格受火工况的抗火试验研究。然而，在实际结构火灾中，楼板和钢梁多同时受火，单一受火的工况并不多见。因此，自制火灾试验炉，开展了钢框架结构中四区格（2×2）和钢梁同时受火的试验研究，其中梁柱节点、钢柱以及炉墙外围边梁均未受火。此外，鉴于火灾试验费用高、周期长，深入开展受火钢筋混凝土楼板理论分析及数值模拟研究具有重要的现实意义。本文主要完成以下几个方面的工作：（1）基于Borland C++6.0软件平台，采用面向对象设计方法和非线性温度场有限元理论，开发了考虑水分影响的温度场分析程序，采用若干试验结果验证了程序的有效性。（2）参照工业炉设计准则，自制火灾试验炉，对整体结构中楼板和钢梁的火灾行为进行了试验研究；简要介绍了试验炉设计情况、温度及变形测量方案，描述了试验现象、楼板裂缝以及节点、填充墙等破坏特征，主要分析了不同结构单元（楼板、钢梁和钢柱）的温度和变形规律，与相关试验结果进行了对比分析。结果表明，受火板格的开裂模式取决于其自身边界条件，非受火板格开裂模式取决于受火板格的数量和位置；相比单一受火钢梁构件，由于受到周围结构单元的约束作用，结构中钢梁具有较强的抗火承载能力；对比高强度螺栓连接节点，混合连接节点有效防止受火钢梁发生局部屈曲。最后，采用温度场非线性程序对楼板温度场进行了数值分析，计算结果和试验结果吻合较好。（3）基于塑性铰线理论，考虑塑性铰线处钢筋合力的竖向分量，结合板的配筋率，提出常温下钢筋混凝土板达到极限状态的应力和变形判断准则，利用改进板块平衡法对钢筋混凝土简支板的极限状态进行对比分析。结果表明，极限承载力计算值与试验结果吻合较好；与试验极限位移相比，极限位移计算值相对保守。此外，通过力学分析，解释了在相同挠度下方板极限承载力小于矩形板的破坏机理。考虑温度对材料特性的影响，将常温改进模型推广到高温状态，建立改进的受火钢筋混凝土板极限承载力计算模型，建议变形破坏准则取为l/30，使得计算结果偏于保守。（4）基于大挠度板单元、三维退化壳单元以及弹塑性理论，建立了常温和高温下钢筋混凝土板有限元分析方法，编制钢筋混凝土双向简支板非线性分析程序。对常温下钢筋混凝土双向板数值分析，考察了板底裂缝模式及拉压薄膜力分布图，探讨了钢筋混凝土板的受拉薄膜作用机理；分析轴向约束混凝土试件的应力—温度曲线变化规律，指出了瞬态热应变作用机理及其重要性；基于瞬态热应变单轴模型，提出瞬态模量的概念，建立瞬态热应变双轴计算模型，结合热弹塑性本构理论，对钢筋混凝土双向板的火灾行为进行了数值分析，揭示钢筋混凝土双向板的三阶段变形模式及每一阶段的力学机理；对火灾下钢筋混凝土板变形行为进行参数分析，结果表明自由膨胀应变和材料性能退化是影响钢筋混凝土板火灾行为的主要因素；混凝土瞬态热应变、钢筋蠕变及其破坏应变对钢筋混凝土板后期火灾行为有重要影响。研究表明，本文数值模型能够较好地模拟钢筋混凝土双向板火灾行为，这为进一步研究整体结构中楼板抗火性能提供了良好的分析平台。更多还原

【Abstract】 Reinforced concrete structures are often used in the buildings due to a numeberof advantages over other construction materials. However, the material properties ofconcrete have been singificantly affected by the high temperature, sometimes thestructure collapse will occur. In recent years, many researchers have paid wideattention to the fire-resistant performance of the concrete structures or members.Recently, to further understand the fire behavior of structural members, ourteam has conducted several fire tests on one panel in a full-scale steel-framedbuilding. However, this case does not represent a real fire situation in a buildingbecause the steel beams are awalys subjected to fire. Therefore, a fire test furnacewas built to heat the four panels (two by two) and steel beams, and all of thebeam-to-column connections and columns were protected from direct fire exposureand the supporting members at the perimeters of the furnace wall were placed toavert fire. Additionally, the cost of fire tests is very high as well as long period. It isvery important to have analytical and numerical methods that can predict thebehavior of reinforced concrete slabs in fire.The main contents are listed as follows:(1) Based on Borland C++6.0and the object-oriented method, the nonlinearfinite element model, in which the moisture was taken into account, has beendeveloped with a computer program, and several comparisons were carried out todemonstrate the efficiency of this program.(2) According to the industrial furnace principle, a special furnace wasdesigned to study the fire behavior of floor slab and steel beams in a buidling. Thispaper briefly presents the furnace, temperature measurement, deflectionmeasurement. The experimental phenomena were discussed in detail as well as thefloor crack characteristic, joint fracture and filled wall crack. The temperaturedistribution of structural elements (floor, steel beams and columns) were mainlyanalyzed, together with their displacements, the present results were also comparedwith the other testing results. The test indicates that the cracking patterns in theheated panels depend on the restraint conditions, the number and locations of theheated panels in the floor have a considerable influence on the cracking patterns ofunheated panels. Also, the steel beams show better fire-resistant performance thanthat indicated in standard fire tests depending on their structural integrity and theinteraction between structural members. Unlike the high-strength bolt connections,the welded-bolted connections did not cause local buckling of the steel beams in fire.Finally, the floor temperature was simulated by the nonlinear temperature program, and the predictions agreed well with the testing results.(3) According to the yield-hinge line theory, the vertical component of steelforce was considered in the developed model. Based on the reinforcement ratio ofreinforced concrete slabs, two failure criteria (deflection and stress) were proposedto determine the load and displacement of the slabs. The effectiveness of thedeveloped model was validated through satisfactory comparison with testing results.The results show that the calculated carrying capacity of the slab was agreementwith the tests, and the calculated limit displacement was relatively conservative.Addtionally, according to the mechanical analysis, the model also explained thefailure mechanism that the limit carrying capacity of the square slab was lower thanthat of the rectangular slab under the same deflection.The above method can easily be adapted for analyzing the ultimate loads of theconcrete slabs in fire, through incorporating the thermal effects on the materialproperties. To obtain the conservative results, it is suggested that the deflectionfailure criterion can be considered to be l/30.(4) Based on the shell elements (flat and three-demensional degenerated) andthe elasto-plastic theory, the nonlinear finite element model was developed tosimulate the structural behaviour of the reinforced concrete slabs at ambient andelevated temperatures.The proposed model has been used to predict the structural behavior ofreinforced concrete slabs at ambient temperature, the predicted bottom layer crackpatterns were discussed and distributions of the membrane tractions were presentedto illustrate the tensile membrane action. The paper discussed the stress-temperaturebehavior of restrainted concrete specimens, and this was used to demonstrate theimportance of the transient strain as well as its mechanism. According to the unaxialtransient strain, this paper proposed transient strain model of concrete with transientmodulus under the biaxial stress state. The propsed model was used to simulate thefire behavior of the slab, and the three-stage response mode was revealed as well asthe mechanism of each stage. The free thermal strain and the material degerationhave significant influence on the fire behavior of reinforced concrete slabs. Theconcrete tranisent strain, the steel creep strain and its crush strain have played animportant part in the later fire behaviour of the slabs.In all, the results show that the propsoed model can be used to analyze the firebehavior of the slabs and the simulation system offers an efficient platform toinvestigate the fire behavior of floor in the building.更多还原