【作者】 杨志年；

【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】 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尚不完善。单个构件抗火试验可以为结构抗火设计提供初步的数据支持和理论指导，但是单个构件与真实整体结构中构件的受力情况、边界条件并不相同，整体结构中相邻构件间的相互作用以及其它部分对构件的约束作用可以对构件的火灾行为产生不同的影响。基于上述原因，本文开展了对足尺四边简支双向板、四边固支双向板以及足尺钢框架整体结构中钢筋混凝土双向板的抗火性能研究，主要研究内容如下：（1）开展了足尺四边简支双向板和足尺四边固支双向板在恒载升温条件下的抗火性能试验。试验测量了火灾作用下板的竖向挠度和平面内位移、沿板厚度混凝土温度场的分布及钢筋温度的变化、考察了固支板板边处约束反力的变化，分析了火灾下板的裂缝开展规律以及破坏特征。结果表明：火灾下四边简支双向板分别在板顶的长跨跨中和1/4跨度处出现三条与短跨方向平行的主裂缝，四边固支双向板在板顶沿板边形成椭圆型塑性铰线；四边固支双向板的抗火性能优于四边简支双向板。（2）利用传统塑性铰线理论对板的极限承载力计算时无法考虑受拉薄膜效应的影响，计算值偏保守。本文在传统塑性铰线理论的基础上，根据板块平衡法和能量法的计算原理，认为受拉薄膜效应是由塑性铰线截面处钢筋合力的竖向分量或钢筋伸长做功所引起，提出了考虑受拉薄膜效应的火灾下钢筋混凝土双向板极限承载力计算方法；基于试验结果，利用改进的板块平衡法和能量法对无水平约束的四边简支双向板和四边固支双向板在火灾下的极限承载力进行了计算，结果表明：本文所提出方法的计算结果与试验结果吻合很好。（3）利用自行研制的火灾试验炉，开展了1栋3层3×3跨足尺钢框架整体结构中的角区格板和中区格板的火灾试验，并对其火灾行为进行了研究。结果表明：火灾下整体结构中相邻构件间的相互作用以及周边相邻构件的约束对板的火灾行为影响显著；角区格板在板顶靠近内板边的1/4跨度处（板顶负弯矩钢筋截断处）出现对板的力学行为有较大影响的主裂缝，中区格板在板顶沿板边形成圆型塑性铰线；由于结构连续性及相邻构件间的互相约束，与受火板相邻的未受火板顶也出现了规则裂缝；整体结构中钢筋混凝土双向板具有较好的抗火性能。（4）开展了将声发射技术用于火灾下整体结构中钢筋混凝土双向板的破坏监测研究。考察了火灾作用下板的声发射事件数、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。结果表明：利用事件数、能量率、b值等参数可以准确区分火灾下钢筋混凝土双向板的裂缝早期开展阶段、裂缝集中出现阶段以及裂缝缓慢扩展阶段；火灾下板的声发射参数产生突变时，如能量率突然升高、b值突然下降等，表征结构可能出现破坏，应给予足够关注。（5）开展了火灾下整体结构中钢筋混凝土双向板的振动特性研究。通过快速Fourier转换，分析了火灾作用下板的频率变化。结果表明：火灾下整体结构中相邻构件对受火板的约束作用对板频率的影响较为显著；火灾下整体结构中中区格板的频率明显高于角区格板；火灾中角区格板和中区格板的频率均有不同程度下降，角区格板的频率下降幅度高于中区格板。更多还原

【Abstract】 Two-way reinforced concrete (RC) slabs bear complicated forces under fireconditons, and there are many affecting factors. For now, however, the relevantexperimental and theoretical researches are imperfect and insufficient. Fire testsperformed on single isolated structural members are the necessary first step tosupport the structural fire resistance design. However, such tests do not reflect thereal behaviour of the elements in the whole structure under fire conditions.Interactions between different structural elements in a whole structure can alter theloading and support conditions of any structural element. This alteration can lead tocompletely different structural behaviour from that based on the initial set ofloading and boundary conditions. Based on the above consideration, thisdissertation studies the fire-resistance properties of full-scale two-way simplysupported RC slab, two-way RC slab with edges clamped and two-way RC slabs ina complete building. The main contents are summarized as follows:(1) Two fire tests were conducted on full-scale two-way simply supported RCslab and full-scale two-way RC slab with edges clamped respectively. The verticaldeflections and horizontal displacements of the slabs, temperature distributionalong the slab depth and temperature variation of the steel reinforcement weremeasured during the tests. The variation of constrained force at the edges of theslab with edges clamped is investigated. The cracking and failure characteristic ofthe slabs are analyzed. The test results indicate that three main cracks parallel to theshort span direction occurred on the top surface of the two-way simply supportedslab, and they were located at approximately the mid-span and1/4span of the longspan of slab. Plastic hinge lines of ellipse shape formed on the top of the slab withedges clamped. The fire resistance of the two-way RC slab with edges clamped wasbetter than that of the two-way simply supported RC slab.(2) The influence of tensile membrane action on the load-carrying capacity ofRC slabs is not incorporated in the conventional yield line theory, and thecalculated result of the load-carrying capacity of RC slab is conservative. In thisdissertation, based on the conventional yield line theory, the tensile membraneaction is assumed to be provided by the vertical component of the steel forces at the section of yield lines or the plastic energy dissipation due to the extension ofreinforcements along yield lines. Then, a new model is proposed to estimate theload-carrying capacity considering the influence of tensile membrane action underfire conditions. Based on the test results, the load-carrying capacity of the two-waysimply supported RC slab and two-way RC slab with edges clamped is estimated byimproved segment equilibrium and energy method. Comparison between thedeveloped model and test results shows good correlation.(3) The specially designed furnaces were used, and two full-scale fire testswere conducted on a corner and an interior panel in a three-storey steel-framedbuilding. The structural fire behaviour is studied. It is shown that interactionsbetween different structural elements and the restraint provided by the adjacentstructural members had significant effect on the structural fire behavior of the slabin a whole structure. For the corner panel, main cracks which had significantinfluence on the structural behaviour occurred on the top of the slab, and they werelocated at approximately the1/4span near the interior edges of the slab (theposition where the top reinforcing bars were broken). For the interior panel, plastichinge lines of circular shape appeared on the top surface of the slab. Because of thesstructural continuity and interaction between structural members, regular cracksalso occurred on the top of the adjacent unheated panels. The two-way concrete slabin a whole structure had good fire performance.(4) Acoustic emission technique was used for monitoring the failure of two-way RC slabs in a whole structure under fire conditions. The changes of parametersof event, energy rate and b value are investigated. The relationship between theseparameters and the cracking of slabs, furnace temperatures and the verticaldeflections are analyzed. The results indicate that the early stage of cracking, thestage of extensive cracks occurring and the stage of cracks propagating slowlycould be distinguished accurately by analyzing these parameters. When theseparameters change abruptly, such as the sudden rise of energy rate and suddendecrease of b value, some structural failure may occur, and these moments shoud behighly concerned in fire.(5) The vibration properties of two-way RC slabs in a whole structure underfire conditions are studied. By means of the fast Fourier transform (FFT) technique,the frequency of the RC slabs in fire is analyzed. The results indicate that therestraint provided by the adjacent structural members had significant effect on the frequency of the two-way RC slab in a whole structure. The frequency of theinterior panel was higher than that of the corner panel. The frequency of the slabsdecreased to various degrees under fire conditions, and the frequency decreaseamplitude of the corner panel was higher than that of the interior panel.更多还原