【作者】 朱崇绩；

【导师】 董毓利；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2012， 博士

【摘要】 火灾时钢筋混凝土双向板起着重要作用，除自身受到高温作用外，还要防止火势蔓延和结构倒塌，而火灾下钢筋混凝土双向板受力复杂，且影响因素多，目前相关的试验及理论研究不完善。本文在国家自然科学基金面上项目“结构中钢筋混凝土双向板火灾行为研究”(批准号：51178143)和“结构构件火灾时声发射和振动特性的试验研究”(批准号：50878069)的资助下，开展了对足尺邻边简支邻边固支双向板、仅在柱上有梁的双向板楼盖和平板无梁楼盖的抗火性能研究，既可为钢筋混凝土双向板的抗火设计提供数据支持和理论指导，又可为消防工作提供参考。主要开展了以下几方面的研究工作：（1）试验研究足尺抗火试验可以准确反映钢筋混凝土双向板的抗火行为，本文对足尺邻边简支邻边固支双向板、仅在柱上有梁的双向板楼盖和平板无梁楼盖进行了恒载升温的试验研究。三种形式的板各制作了2个试件，试验测量了火灾作用下板的平面内位移和竖向位移等，考察了板的约束反力变化，分析了沿板厚度混凝土温度场的分布以及钢筋的温度变化。试验结果表明：火灾后邻边简支邻边固支双向板的顶部裂缝形成半椭圆形的破坏形式，仅在柱上有梁的双向板楼盖最终呈凹口向上的“球冠”形破坏，平板无梁楼盖的板顶裂缝最终为对角呈双曲线形的破坏形式。单面受火的钢筋混凝土板沿截面厚度方向混凝土温度场呈非线性分布，温度梯度随时间的增长而快速增大，并且水分的影响使混凝土在100℃时产生了一个升温水平段；水分不仅影响了混凝土的升温，还使受火混凝土产生爆裂，含水率太高时板将因混凝土的爆裂而导致破坏。（2）极限承载力计算传统塑性铰线理论对板的极限承载力计算时不能考虑薄膜效应，计算值偏保守，为了正确计算钢筋混凝土板的极限承载力，本文在传统塑性铰线理论的基础上，根据板块的受力平衡，提出了考虑张拉薄膜效应的板块平衡法计算火灾下邻边简支邻边固支双向板的极限承载力；根据板的内力和外力做功平衡，提出了考虑张拉薄膜效应的能量法计算火灾下平板无梁楼盖和邻边简支邻边固支双向板的极限承载力。火灾下板的受拉薄膜效应在塑性铰线形成后才出现，在板块平衡法中，认为板的张拉薄膜力是由塑性铰线上钢筋的竖向分力提供的，而在能量法中，认为板的张拉薄膜效应是由塑性铰线上钢筋的伸长所做塑性功引起。本文所提出方法的计算结果与试验结果吻合很好。在混凝土受压薄膜效应的作用下，仅在柱上有梁的双向板楼盖的板内形成“拱”作用，板的竖向位移在“拱”作用下向上发展，其破坏最终为梁内侧提供受压薄膜力截面上混凝土的压碎破坏。（3）板的声发射特性为了监测火灾作用下板的破坏特征，本文提出了将声发射技术用于火灾下邻边简支邻边固支双向板、仅在柱上有梁的双向板楼盖和平板无梁楼盖的破坏监测研究。考察了火灾作用下板的声发射事件率、能量率和b值的变化，分析了各参数与板的裂缝开展、炉温及竖向位移等的关系。研究结果表明，利用事件率、能量率、b值等参数可以对火灾下钢筋混凝土双向板和双向板无梁楼盖的第一和第二条裂缝的出现做出准确的判断，由于新出现的裂缝与已有裂缝的扩展相重叠，所以并不能区分所有裂缝，但可以准确区分板的裂缝开裂前阶段、裂缝集中出现阶段以及裂缝缓慢扩展阶段。（4）板的振动特性火灾下板的振动特性是其本身的特性，所以本文对火灾下邻边简支邻边固支双向板、仅在柱上有梁的双向板楼盖和平板无梁楼盖的振动特性进行了研究。通过快速Fourier转换，结合数值计算，分析了火灾作用下板的频率变化。结果表明，火灾下邻边简支邻边固支双向板、双向板楼盖和双向板无梁楼盖在火灾作用下频率大幅降低，到停火时这三种形式板的频率下降幅度分别为39.7%、52.7%和42.5%。通过回归分析，本文给出了火灾下三种形式板的频率与板中心竖向位移的关系式。更多还原

【Abstract】 Two-way reinforced concrete slabs are of great importance in the prevention of fireaccidents. Other than bearing the high temperature effect, they also need to prevent firespread and collapse of the building structure. The force interactions in two-wayreinforcement concrete slabs under fire conditions are complicated, and there are manyaffecting factors. The relevant experiment and theory are imperfect. Supported by theNational Natural Science Foundation Projects “Fire Behavior of Two-way ReinforcedConcrete Slabs in Whole Structure”(Grant Number:51178143) and “Study on AcousticEmission and Vibration Characteristics of Structural Members in Fire”(Grant Number:50878069), this dissertation studies the fire-resistance properties of full-scale two-wayreinforced concrete slabs, which include slabs with two edges being clamped and twoedges being simply supported, two-way RC slabs and flate-plate floors slabs. It canprovide data support and theoretical guidance for the design of two-way reinforcementconcrete slabs with fire resistance, and offers reference for fire fighting. My workincludes:(1) Experiment study. The fire resistance of two-way reinforced concrete slabscould be reflected accurately by full-scale experiment. In this dissertation, We testfull-scale slabs, slabs with two edges being clamped and two edges being simplysupported, two-way RC slabs and flate-plate floor slabs which are exposed to elevatingtemperature with constant load. Two samples were made for the three different slabs. Theedge horizontal deflection and vertical deflection of slabs under fire are measured, thevariation of constrained force is recorded, the temperature distribution of concrete andtemperature variation of rebars are analyzed. The experiment study indicates that afterfire test, the slabs with two edges being clamped and two edges being simply supportedform cracks on the top surface in a semi-elliptic pattern，A spherical crown shape withnotch upward failure mode is formed of the two-way RC slabs, and the top surface cracksformed in a hyperbolic pattern between every diagonal columns of the flate-plate floor.The temperature field distribution along vertical direction of the slab with single surfacebeing exposed to fire is nonlinear and the temperature variation increases quickly by time.There is a plateau in the temperature rise at100℃level attributed to the existence ofmoisture. Not only this, moisture also leads to spallings of concrete, which will furtherlead to slab destruction if its rate is too high.(2) Calculation of limit load carrying capacity of slabs. The classical yield linetheory does not consider the membrane effect in calculating the limit load carryingcapacity of slabs, and the result was conservated. We take into account the membraneeffect and present several new ways for different slabs in this dissertation: Based on theclassical yield line theory and the force equilibrium, we give a segment equilibrium method when dealing with two-way slabs with two edges being clamped and two edgesbeing simply supported, and based on work equilibrium of internal and external force, wealso give an energy method to flate-plate floor and two-way slabs with two edges beingclamped and two edges being simply supported. The membrane effect shows only afterthe formation of mechanism of plastic hinge lines of slabs in fire. The segmentequilibrium method thinks the tensile membrane to be caused by the vertical componentof tensile force of reinforcements at the yield line section, and the energy method thinksthe tensile membrane to be caused by the plastic work of reinforcements at the yield linesection. The results calculated from our methods agree with experiments very well. Archaction was formed under the effect of compressive membrane force, which leads thevertical displacement upwords. And the damage of the two-way RC slab is the crushingof concrete at the compressive membrane force sections next to the inner side of thebeam.(3) Research on acoustic emission properties of slabs. In order to monitor the failureproperties of slabs under fire conditions, we propose to use Acoustic Emission techniqueto monitor the failure of these three types of slabs at elevated temperature. The changesof parameters of event rate, energy rate and b value, are investigated. And the relationbetween these parameters and the crack of slabs, temperature of the furnace and thevertical deflection are analyzed. The results indicate that，using these parameters, we caneasily tell the occurrence of the first and the second crack of the three different two-wayreinforced concrete slabs. Because of the overlapping of the occurrence of new cracksand the extension of old cracks, it is not easy to distinguish every crack，but theseparameters can accurately tell the three stages of the cracks：the stage before cracks occur,the stage when extensive cracks occur and the stage of when cracks extend slowly.(4) Research on vibration properties of slabs. The vibration properties areself-characteristics of slabs in fire. So in this dissertation the vibration properties of thesethree types of slabs at elevated temperature are studied. By means of the Fast FourierTransform (FFT) technique and numerical calculation, the frequency of the reinforcedconcrete slabs in fire is analyzed. The results indicate that, there is a large decrease infrequency under fire conditions. The decrease amplitude after fire is39.7%,52.7%and42.5%for each type respectively. We analyze relations between frequency and thecentral vertical deflection of the three different slabs by regression method in thisdissertation.更多还原