火灾下及火灾后约束混凝土双向板承载性能研究

发布时间：2018-09-17 16:01

【摘要】：由于火灾试验费用高昂,目前关于楼板的抗火性能研究尚不够充分,约束作用下钢筋混凝土双向板的火灾试验少之又少。此外,多数火灾在局部蔓延时即被扑灭,加之混凝土热惰性对建筑结构、构件的保护作用,火灾后建筑物修复加固的可能性较大。为更加深入地理解约束钢筋混凝土双向板的抗火性能,了解火灾后该构件的力学性能,开展了火灾下(后)约束钢筋混凝土双向板的承载性能试验研究和理论分析。主要工作如下:(1)基于已有模型或相关文献试验数据,不考虑混凝土骨料类型、钢筋强度和钢筋等级等因素,归纳和总结了高温下和高温后混凝土和钢筋的材料力学性能,提出了混凝土和钢筋在高温下和高温冷却后的力学性能模型。(2)对1块面内约束和角部约束钢筋混凝土双向板进行了抗火性能试验,对混凝土截面温度、钢筋温度、平面内外位移、板角反力和裂缝开展及破坏模式进行了试验研究。研究表明,面内约束会降低双向板的抗火性能,主要表现在变形速率和面外位移增大;配筋率对楼板的抗火性能有积极作用。研发设计了一套无线测温系统,在电炉试验和火灾试验中与有线测量方式进行了对比试验,试验表明该系统具有可行性。(3)对角部约束火灾后板和未受火板进行了承载性能对比试验,对极限承载力、平面内外位移、钢筋应变、板角反力和裂缝开展及破坏模式进行了试验观察和对比分析。结果表明,火灾后板的极限承载力较未受火板降低较少,但抗变形能力减弱,混凝土脱落现象较为严重。(4)基于经典塑性铰线理论,在李国强模型基础上,提出了常温时不同配筋率下的钢筋破坏和混凝土压碎破坏两种计算模型。钢筋破坏模型中,对板中间椭圆钢筋网简化成矩形钢筋网,并提出钢筋极限应变差破坏准则,通过与试验结果和其他模型比较验证合理,且极大地简化了计算过程。混凝土压碎模型对截面内混凝土强度和受压区域进行了假定,计算结果较好,可以为钢筋混凝土双向板的承载能力评估提供参考。(5)对常温下双向板计算模型进行了高温下和高温后修正,并考虑面内约束作用,建立了约束双向板计算模型。结果表明:面内约束力越大,双向板极限承载力降低越大;双向面内约束力较单向面内约束力对板的极限承载力降低幅度大,且降低幅度大于单向约束力的2倍。
[Abstract]:Due to the high cost of fire test, the research on fire resistance of floor slab is not enough, and the fire test of reinforced concrete two-way slab under restraint is rare. In addition, most of the fires are extinguished when they are spread locally, and the thermal inertia of concrete can protect the building structure and components, so it is possible to repair and reinforce the building after the fire. In order to better understand the fire resistance of confined reinforced concrete two-way slabs and understand the mechanical properties of the members after fire, the experimental study and theoretical analysis of the bearing capacity of reinforced concrete bidirectional slabs under fire were carried out. The main work is as follows: (1) based on the existing model or related literature test data, the mechanical properties of concrete and steel bar under high temperature and after high temperature are summarized and summarized without considering the type of concrete aggregate, the strength of steel bar and the grade of steel bar, etc. The mechanical performance model of concrete and steel bar under high temperature and high temperature cooling is put forward. (2) the fire resistance test of a reinforced concrete bidirectional slab with in-plane and corner restraint is carried out, and the temperature of the section of concrete and the temperature of steel bar are tested. The internal and external displacement, plate angle reaction force, crack development and failure mode are studied experimentally. The results show that the in-plane constraint can reduce the fire resistance of the bidirectional slab, which is mainly reflected in the increase of the deformation rate and the out-of-plane displacement, and the reinforcement ratio has a positive effect on the fire resistance of the floor. A wireless temperature measuring system has been developed and designed, which is compared with wired measurement in electric furnace test and fire test. The test results show that the system is feasible. (3) the load-bearing capacity of the plate after the corner restrained fire is compared with that of the plate without fire, and the ultimate bearing capacity, the displacement inside and outside the plane, the strain of steel bar are tested. The experimental observation and comparative analysis of plate angle reaction force and crack development and failure mode were carried out. The results show that the ultimate bearing capacity of the plate after fire is less than that of the unburned slab, but the deformation resistance is weakened, and the phenomenon of concrete shedding is more serious. (4) based on the classical plastic hinge theory and Li Guoqiang's model, Two calculating models of steel bar failure and concrete crushing failure under different reinforcement ratio at room temperature are proposed. In the failure model of steel bar, the elliptical steel mesh in the middle of the slab is simplified into a rectangular steel mesh, and the failure criterion of ultimate strain difference of steel bar is proposed. The results are compared with the experimental results and other models, and the calculation process is greatly simplified. The concrete crushing model assumes the strength and compressive region of concrete in the section, and the calculated results are good. It can provide a reference for the evaluation of the bearing capacity of reinforced concrete bidirectional slabs. (5) the calculation model of bidirectional slabs under normal temperature is modified at high temperature and after high temperature, and the calculation model of constrained bidirectional slabs is established considering the in-plane constraint. The results show that the greater the in-plane binding force, the greater the ultimate bearing capacity of bidirectional plate, and the greater the reduction range of bidirectional in-plane binding force is compared with that of unidirectional in-plane binding force, and the decrease range is more than two times that of unidirectional binding force.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU37

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