A simplified approach for predicting temperature in reinforced concrete members exposed to standard fire

For evaluating fire resistance of a reinforced concrete member, temperature profile in the cross section of the member is required. Current simplified approaches and design graphs do not yield reliable temperature predictions in rebar and concrete. In this paper, a simplified approach is proposed for evaluating cross-sectional temperatures in fire-exposed reinforced concrete members. The approach is derived through statistical nonlinear regression analysis, utilizing data generated from finite element analysis. The parameters that were varied in the finite element analysis include sectional geometry, concrete characteristics and fire exposure conditions. The validity of the approach for different types of concrete is established by comparing predictions from the proposed equation with data from fire tests and finite element analysis. Through these comparisons it is shown that the proposed equation gives better predictions of temperatures in reinforced concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design standards.     

GFRP筋混凝土梁耐火性能计算方法

通过GFRP筋混凝土梁耐火性能的理论分析与有限元计算,提出GFRP筋混凝土结构耐火性能的计算方法。在合理选择GFRP和混凝土材料的热工参数、高温力学参数的基础上,采用有限元分析软件ABAQUS建立三面受火的GFRP筋混凝土梁的高温热力学模型。经与GFRP筋混凝土梁火灾试验结果的对比验证,该高温力学模型具有较高的精确性。对影响GFRP筋混凝土梁高温力学性能的各参数进行有限元分析,结果表明,影响梁耐火性能的主要因素为梁上作用的荷载比、GFRP筋在混凝土截面的位置和受火时间。参考欧洲规范钢筋混凝土抗火性能的设计方法,提出GFRP筋混凝土构件基于力学性能的耐火设计公式。通过混凝土500℃等温线简化受火面积和GFRP筋高温强度等效换算的方式,将火灾下截面的非均匀材料力学性质转变为随受火时间变化的均匀材料,提出了不同受火时刻GFRP筋混凝土受弯构件的承载力计算式。经与有限元分析结果的对比,该计算方法精度较高,可应用于评估不同受火时刻下GFRP筋混凝土的高温承载力。     

CFRP布加固火灾后钢筋混凝土柱的试验研究

通过3根碳纤维增强复合材料(CFRP)布加固ISO 834标准火灾作用后钢筋混凝土柱的性能试验以及3根ISO 834标准火灾作用后未加固的钢筋混凝土柱和3根常温下钢筋混凝土柱的对比试验,研究了CFRP布加固火灾后钢筋混凝土柱的有效性.试验结果表明:CFRP布加固对火灾后钢筋混凝土柱的刚度修复有一定作用,但刚度提高程度有限,从开始加载到荷载达到80％极限荷载的不同加载水平下,加固后轴压试件的轴压刚度与常温下试件刚度的比值在0.25～0.39之间,偏压试件的抗弯刚度与常温下试件刚度的比值在0.14～0.31之间.CFRP布加固对火灾后试件的承载力提高作用较为显著,能将试件的承载力提高至受火后承载力的1.67～2.37倍,但与常温下试件的承载力相比,依然有一定差距,加固后试件的承载力水平为常温下试件的0.54～0.67倍.     

A quality evaluation method for existing carbonated reinforced concrete members

Objective evaluation of the current quality of existing carbonated reinforced concrete members is important as time may degrade their bearing capacity and rigidity. In this paper, a method in which the weight coefficients of every evaluation factor are determined from the coefficients of variation (COVs) or coefficients of dispersion (CODs) of the standard values of every evaluation factor is proposed in order to evaluate the quality of existing carbonated reinforced concrete members. Because it is unnecessary to gather many experts for evaluating every structure, the method should be more practical and applicable in engineering. Finally, an engineering example shows that this method is feasible to solve the problem of quality evaluation of existing carbonated reinforced concrete members.     

Experimental research on post-fire behaviour of reinforced concrete columns

This paper reports an experimental research into the effect of fire exposure time on the post-fire behaviour of reinforced concrete columns. Nine full-size reinforced concrete columns (45×30×300 cm) with two longitudinal reinforcement ratios (1.4% and 2.3%) were unexposed and exposed to the ISO 834 standard fire for 2 and 4 h with a constant preload. One month after cooling, the specimens were tested in axial load combined with uniaxial or biaxial bending. The test results show that the residual load-bearing capacity decreases with increase in fire exposure time. This deterioration in strength following an increase in fire exposure time can be slowed down by the strength recovery of hot rolled reinforcing bars after cooling. In addition, the reduction in residual stiffness is higher than that in ultimate load; consequently, much attention should be given to the deformation and stress redistribution of the reinforced concrete building subject to earthquakes after a fire.     

A simplified approach for predicting temperatures in insulated RC members exposed to standard fire

Fire resistance of concrete structural members can be enhanced through the application of external fire insulation on the surfaces of concrete member. For evaluating fire resistance of such insulated RC members, temperatures in concrete and steel reinforcement are to be known. This paper develops a simplified approach for predicting cross-sectional temperatures in an insulated RC structural member exposed to standard fire. The approach is derived by replacing the insulation layer into an equivalent concrete thickness layer and then undertaking statistical regression analysis on temperature data of modified concrete section. The effect of critical parameters, including geometry of concrete member and insulation, thermal properties of concrete and fire insulation, and duration of fire exposure is accounted for in temperature equations. The validity of the approach is established by comparing predictions from the proposed equation with data generated from fire tests and finite element analysis. These comparisons show the proposed equation gives reasonable prediction of temperatures, within a range of ±10%, in insulated concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design manuals.     

某钢筋混凝土剪力墙结构火灾后检测鉴定

对火灾后钢筋混凝土构件的科学检测、鉴定,是灾后钢筋混凝土构件能否被合理加固修复的重要前提,结合工程实例,对火灾后建筑结构的检测鉴定进行了全过程分析.     

保护层厚度对高温作用下钢筋混凝土构件极限承载力的影响及分析

在钢筋混凝土构件火灾高温作用下极限承载力计算分析的基础上,着重进行保护层厚度对钢筋混凝土构件(梁)高温作用下承载力的影响及定量分析的讨论,由此得出:由于钢筋混凝土构件高温侧钢筋的保护层能在火灾高温作用下显著延缓钢筋温度的升高,所以适当增加保护层的厚度,可以显著提高钢筋混凝土梁在高温下的极限承载力,可用于指导工程耐火设计。     

增大截面法加固高温损伤钢筋混凝土压弯构件承载力和变形的计算

对增大截面法加固的钢筋混凝土压弯构件的受力性能进行了全过程分析,并与试验结果相比较。计算结果表明该计算方法合理、程序可行、计算结果稳定。计算程序可作为火灾后增大截面法加固的混凝土压弯结构的分析或计算的手段。     

FRP加强R/C梁防火性能调查研究

对纤维加强聚合物(FRP)材料加强钢筋混凝土梁在火灾中的防火性能进行了研究。试验结果显示,防火材料能够帮助构件达到标准防火性能,同时对不断增长的FRP应用也很重要。介绍了不同文献对FRP在高温下的性能所做的研究以及目前标准对建筑构件的耐火极限要求。对两个大型试验进行了介绍。试验材料为混凝土梁构件,外部用FRP板加强,并且三分之二用专利耐火隔热材料保护。给出了试验结果,并重点强调了曝火状态下所测得的构件温度。试验数据验证了热传导数值模型,该模型可用于预测加强并绝缘钢筋混凝土梁构件内的温度。试验结果和模型数据显示,正确设计和进行绝缘保护的FRP加强梁构件耐火极限能够达到4h或者以上。     

均匀受火钢筋混凝土框架极限承载力分析

对火灾高温作用下钢筋混凝土梁、柱可能破坏截面的应力、应变及内力进引分析。在此基础上,编制了钢筋混凝土梁、柱在高温作用下截面极限承载力的计算程序。运用该程序对同时受到荷载和均匀受火条件下的简单框架梁、柱可能破坏截面的极限承载力的变化及其相互影响进行计算、分析和讨论,据此提出钢筋混凝土框架在均匀受火时也要像抗震设计一样尽量满足"强柱弱梁"的要求,即"耐火强柱弱梁"的延性设计原则,为火灾抗倒塌设计提供参考。     

钢筋混凝土楼板隔火能力的耐火当量时间

我国现行规范在规定钢筋混凝土楼板耐火极限时,并未考虑火灾荷载和通风条件.从隔热性方面研究了钢筋混凝土楼板的耐火极限,以室内火灾轰燃后的房间热平衡和热传导理论为基础,以钢筋混凝土楼板火灾中背火面的最高温度相等为原则,利用计算机数值分析方法计算出楼板的隔火当量时间,并用最小二乘法回归出当量时间关于火灾荷载密度和开口因子的计算公式,可使设计方法得到简化,为性能化防火设计提供参考.     

钢筋混凝土构件几何尺寸的调查和统计分析

本文根据大量实测数据,依据统计数学提供的方法进行分析,提出了钢筋混凝土结构构件几何尺寸变量的主要统计参数,研究了其概率分布形式,为研究钢筋混凝土结构构件的可靠度提供了分析依据,本文还根据统计分析的结果,对我国现行的国家标准(TJ 321-76)中有关构件几何尺寸允许偏差值的规定进行了对比分析,并对我国当前钢筋混凝土结构构件几何尺寸的实际质量水平作出了评价。     

混凝土骨料种类和边界条件对截面温度场的影响

为了正确分析钢筋混凝土构件截面温度场,以矩形柱为对象,以标准火作用为受火条件,采用数值计算方法,研究混凝土骨料种类和边界条件对截面温度场的影响。研究结果表明:因热参数差别较大,硅骨料构件截面温度明显高于碳骨料,而法国规范推荐混凝土的温度接近硅骨料混凝土的温度,温度值越高其间差别越小;是否考虑边界单元格热储存对温度场影响不大。     

钢筋砼结构抗火性能研究现状与展望

本文作者在大量调研和阅读中外文献的基础上，总结了目前国内外钢筋砼结构抗火性能研究的现状，包括国内外抗火试验研究现状，温度场的计算，构件承载务的计算以及火灾后钢筋砼的检测，加固方法等，介绍了作者的研究成果并展望了今后研究方向。     

某地铁车库火灾后受损板检测鉴定与加固维修研究

以某地铁车库火灾后受损板为例,通过显微结构分析、结构物理力学性能检测、现场原位荷载试验等方法,对火灾后受损板进行了检测鉴定与加固维修研究。研究火灾后受损混凝土结构的检测鉴定内容与方法,为灾后结构的损伤评价及后续的维修与加固提供技术依据。提出了一种火灾后受损结构鉴定评级层次划分与评级标准,可补充火灾后混凝土结构损伤程度的评级问题。根据检测鉴定结果评定火灾受损结构构件的损伤等级,对不同程度受损的结构构件进行了加固与维修设计。通过加固与维修,消除了火灾后结构的安全隐患,提高了结构的承载力与耐久性。     

火灾中混凝土与钢筋之间粘结力的模拟

采用非线性程序,模拟火灾中钢筋混凝土结构中混凝土与钢筋之间的粘结机理。通过1个梁的拉拔力试验、1个特定温度下的梁试验和在两种标准火灾中的4个足尺梁试验,证明数值模型的准确可靠性。该模型对火灾中钢筋混凝土构件和结构响应的预测满足精度要求,粘结连接单元也能满足火灾中钢筋混凝土结构3维分析的计算精度和计算效率的要求。结果表明:混凝土与钢筋之间的粘结条件对钢筋混凝土结构的耐火性能有重要影响,尤其当钢筋的温度较高(大于500°C)时。目前使用的火灾中钢筋混凝土结构粘结条件的假设是偏不安全的。     

火灾后型钢混凝土柱受力性能试验研究

通过6个火灾后型钢混凝土柱的静力加载试验以及2个常温下型钢混凝土柱的对比试验,研究了火灾后型钢混凝土柱的破坏形态、变形特性、剩余承载力、刚度等。试验结果表明：火灾后型钢混凝土柱的破坏形态与常温下基本相同,但柱的轴压刚度、抗弯刚度、承载力均有不同程度降低;从加载到荷载达到80%极限荷载的不同阶段,火灾后型钢混凝土柱轴压刚度影响系数kz约为0.33~0.44,抗弯刚度影响系数kw约为0.30~0.59。利用规程JGJ 138-2001的计算方法,对所有试件常温下的承载力进行了计算,并将试验结果与计算结果进行了对比,经历火灾作用后轴压柱的剩余承载力约为常温下承载力的51%~81%,偏压柱的剩余承载力约为常温下承载力的69%~81%,火灾后型钢混凝土柱承载能力退化显著。     

SRC和RC柱耐火性能和抗火设计的若干问题探讨

扼要介绍了影响型钢混凝土SRC和RC钢筋混凝土柱耐火极限的可能因素主要有截面尺寸、构件长细比、火灾荷载比、截面配筋率、截面含钢率、荷载偏心率、截面高宽比、钢材和混凝土强度等的几何参数、物理参数和荷载参数等对SRC和RC构件.构件耐火极限的影响规律,探讨了SRC和RC柱耐火性能和抗火设计中的若干问题。