钢筋混凝土T形梁及梁—板组合体的耐火性能研究

发布时间：2018-09-16 20:03

【摘要】：钢筋混凝土结构的耐火研究和耐火设计以往大多都是针对独立构件进行的，忽略了结构中相邻构件之间的相互约束效应，这与结构的真实火灾行为存在明显差异。近年来，，国内外学者开展了具有端部约束的钢筋混凝土梁、柱的耐火性能研究，相比以往独立构件无疑是明显进步。除端部约束外，杆系构件沿其长度方向还可能受到其它相邻构件的约束，进而对其火灾行为产生不同程度的影响（例如，梁侧楼板不可避免地会对梁的火灾行为产生影响），但国内外对此还鲜见研究报道。作为初步探讨，本文以钢筋混凝土梁及其相邻楼板作为研究对象，从明火试验、数值模拟、参数分析和实用计算方法等方面，初步考察了钢筋混凝土T形梁及梁-板组合体的耐火性能。本文的主要工作和结论如下： 1.开展了6根足尺钢筋混凝土简支T形梁和2根对比矩形梁的明火试验，考察了荷载比、板宽等参数对简支T形梁高温破坏特征、高温变形及耐火极限的影响趋势。试验表明：荷载比较大时随着板宽增加，简支T形梁的耐火极限总体上随之增大；板宽相同时随着荷载比增加，简支T形梁的耐火极限减小。 2.利用经过前人和试验数据验证过的SAFIR软件，开展了钢筋混凝土简支T形梁的耐火极限增大系数分析，考察了荷载比、梁跨高比、梁受拉纵筋配筋率、梁保护层厚度、板保护层厚度、板宽、板厚、板受拉纵筋配筋率等参数对该增大系数的影响规律；基于1296种工况的计算结果，建议给出了简支T形梁的耐火极限增大系数的实用计算方法。研究表明：随着荷载比和梁跨高比增加，简支T形梁的耐火极限增大系数总体呈现出逐渐增大的趋势；随着梁受拉纵筋配筋率和梁保护层厚度增加，该增大系数逐渐降低；随着板宽增加，该增大系数呈现出开始增长较快随后基本保持不变的变化趋势；随着板保护层厚度增加，该增大系数迅速增大；但在常用取值范围内，板厚和板受拉纵筋配筋率对该增大系数影响较小。 3.在合理假设基础上，分别推导给出了从空间框架中抽取出的梁-板组合体的板边侧向约束刚度和板边转动约束刚度的简化计算公式；通过算例对比，验证了上述简化公式具有较好精度。 4.开展了9根具有梁端约束的足尺钢筋混凝土T形梁的明火试验，考察了升降温作用下梁端轴向和转动约束、荷载比、板宽等参数对约束T形梁高温破坏特征、变形及内力的影响趋势。试验表明：升降温结束后约束T形梁存在较明显的残余轴压力和一定的残余轴向变形；随着梁端轴向和转动约束刚度比同时增加，约束T形梁的竖向挠度峰值总体差别不大；荷载比为0.3时，约束T形梁的轴压力峰值随板宽增加略有增大，但荷载比为0.5时，板宽增加对轴压力峰值影响不明显；板宽改变对约束T形梁的梁端弯矩和最大弯矩比影响有限。 5.利用SAFIR软件，开展了同时具有梁端约束和板边约束的钢筋混凝土梁-板组合体的耐火性能分析，考察了梁端轴向约束刚度、梁端转动约束刚度、板边侧向约束刚度、板边转动约束刚度、板宽等参数对具有边界约束的梁-板组合体的高温变形和内力的影响规律。研究表明：随着梁端轴向和转动约束刚度以及板边侧向和转动约束刚度的增加，梁轴力均有所增大；对梁端弯矩、梁跨中挠度和板中心点挠度而言，梁端转动约束刚度的影响较大，而梁端轴向约束刚度、板边侧向约束刚度和板边转动约束刚度的影响有限；随着板宽增加，梁轴力减小，但梁端弯矩、梁跨中挠度和板中心点挠度却随之增大。 6.由于钢筋混凝土构件的非线性行为，实际火灾中相邻构件之间的约束作用往往是时变的。由于时间和篇幅有限，作为考虑时变约束的第一步，本文对具有端部时变约束的矩形梁的耐火性能进行了计算分析，以期为后续具有时变约束的T形梁及梁-板组合体的耐火研究奠定基础。首先考察了梁端时变轴向约束刚度和时变转动约束刚度的变化趋势，在此基础上探讨了时变约束对矩形梁升降温全过程轴力和梁端弯矩的影响规律。研究表明：高温下时变轴向约束梁的最大轴力比小于定常轴向约束梁的相应值，轴向约束刚度比初值越小二者相差越大；高温下时变轴向约束梁的最大梁端弯矩与定常轴向约束梁几乎相同；时变转动约束下梁轴力比和梁端弯矩随升降温时间的变化曲线都与定常转动约束下的相应曲线一致。
[Abstract]:Fire resistance research and fire resistance design of reinforced concrete structures are mostly carried out for independent members in the past, ignoring the mutual restraint effect between adjacent members in the structure, which is obviously different from the real fire behavior of the structure. In recent years, scholars at home and abroad have carried out the fire resistance of reinforced concrete beams and columns with end restraint. In addition to the end restraint, the member may also be restrained by other adjacent members along its length direction, which will have different degrees of influence on its fire behavior (for example, the beam side floor will inevitably have an impact on the beam fire behavior), but there is little research on this at home and abroad. As a preliminary study, this paper takes reinforced concrete beams and their adjacent floors as research objects, and preliminarily investigates the fire resistance of reinforced concrete T-shaped beams and beam-slab composites from the aspects of open fire test, numerical simulation, parameter analysis and practical calculation methods.
1. Six full-scale reinforced concrete simply supported T-shaped beams and two comparative rectangular beams were tested under open fire. The influence of load ratio, slab width and other parameters on high temperature failure characteristics, high temperature deformation and fire resistance limit of simply supported T-shaped beams were investigated. When the plate width is the same, the fire resistance of simply supported T beams decreases with the increase of load ratio.
2. By using the SAFIR software verified by predecessors and test data, the fire resistance limit increase coefficient of reinforced concrete simply supported T-shaped beam is analyzed. The influence of load ratio, beam Span-to-height ratio, ratio of longitudinal reinforcement, thickness of protective layer, thickness of protective layer, width, thickness and ratio of longitudinal reinforcement on the increase coefficient is investigated. Based on the calculation results of 1296 kinds of working conditions, a practical calculation method for the fire resistance limit increase coefficient of simply supported T-shaped beam is proposed. With the increase of thickness, the coefficient of increase decreases gradually; with the increase of slab width, the coefficient of increase presents a trend of rapid initial increase and then basically remains unchanged; with the increase of the thickness of the protective layer, the coefficient of increase increases rapidly; but within the range of commonly used values, the thickness of the slab and the ratio of longitudinal ribs have little influence on the coefficient of increase.
3. On the basis of reasonable assumptions, the simplified formulas for calculating the lateral restraint stiffness and the rotational restraint stiffness of the plate edge of the beam-plate composite extracted from the space frame are derived and given respectively.
4. Experiments on 9 full-scale reinforced concrete T-shaped beams with beam-end restraints were carried out under open fire. The effects of axial and rotational restraints, load ratio and plate width on the high-temperature failure characteristics, deformation and internal forces of the restrained T-shaped beams were investigated. The results show that the restrained T-shaped beams have obvious residual axes after heating and cooling. The peak value of the vertical deflection of the restrained T-shaped beam varies little with the increase of the ratio of axial and rotational restrained stiffness at the end of the beam. When the load ratio is 0.3, the peak value of the axial pressure of the restrained T-shaped beam increases slightly with the increase of the plate width, but when the load ratio is 0.5, the increase of the plate width has no obvious effect on the peak value of the axial pressure. The change of slab width has limited influence on the bending moment and maximum bending moment ratio of restrained T beam.
5. The fire resistance of RC beam-slab composite with both beam-end constraint and plate-edge constraint is analyzed by using SAFIR software. The axial restraint stiffness, beam-end rotational restraint stiffness, lateral restraint stiffness, plate-edge rotational restraint stiffness, plate width and other parameters of beam-slab composite with boundary constraint are investigated. The results show that the axial force increases with the increase of the axial and rotational restraint stiffness at the end of the beam, the lateral and rotational restraint stiffness at the edge of the plate, and the rotational restraint stiffness at the end of the beam has a greater influence on the bending moment at the end of the beam, the midspan deflection and the central point deflection of the plate, while the axial restraint stiffness at the end of the beam and the lateral and rotational restraint stiffness at the The influence of restraint stiffness in direction and rotational restraint stiffness at the edge of the plate is limited; with the increase of the width of the plate, the axial force of the beam decreases, but the bending moment at the end of the beam, the midspan deflection and the center deflection of the plate increase.
6. Because of the nonlinear behavior of reinforced concrete members, the constraints between adjacent members are often time-varying in actual fires. As the first step to consider time-varying constraints, the fire resistance of rectangular beams with end-varying constraints is calculated and analyzed in this paper, with a view to providing time-varying constraints for subsequent T-beams. Firstly, the variation trend of time-varying axial restraint stiffness and time-varying rotational restraint stiffness at the end of the beam is investigated, and then the influence of time-varying restraint on the axial force and bending moment at the end of the rectangular beam in the whole process of heating and cooling is discussed. The axial force ratio is smaller than the corresponding value of the stationary axial restrained beam, and the axial restrained stiffness ratio is smaller than the initial value. The maximum bending moment of the time-varying axial restrained beam at high temperature is almost the same as that of the stationary axial restrained beam. The corresponding curves are consistent.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU375

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