矩形钢管混凝土柱的防火保护

简要介绍了关于火灾下矩形钢管混凝土柱力学性能的研究成果。对构件耐火性能的实验情况、影响耐火极限的重要因素和确定厚涂型方钢管混凝土保护层厚度的实用计算方法作了详细说明 ,并结合工程中矩形钢管混凝土柱的抗火设计实例 ,说明规程课题组提出的抗火设计方法的有效性。研究成果可为有关矩形钢管混凝土工程进行抗火设计时提供参考     

混凝土及预应力混凝土结构抗火设计建议

本设计建议包含耐火极限、材料选择、结构构件形式、混凝土抗火保护层厚度、预应力筋及非预应力筋配置、爆裂验算及防爆裂措施、火灾下两类极限状态的验算及相关配筋构造等方面,对混凝土及预应力混凝土结构提出了抗火设计与验算建议.     

闭口型压型钢板-再生混凝土组合楼板抗火性能研究

闭口型再生混凝土组合楼板兼具组合结构的优点与固废利用的特点，但高温下再生混凝土热工和力学性能与普通混凝土有明显差别，进一步造成了相应结构构件火灾下抗火性能的差异。为此，对闭口型再生混凝土组合楼板基于承载能力的耐火极限进行了试验与有限元研究，主要参数为再生粗骨料取代率、板型与荷载水平，分析挠度与不同位置处的温度发展，并建立了适用于该类楼板耐火极限简化计算方法。结果表明：受火90 min后，压型钢板与混凝土未发生分离，组合楼板保持了较好整体性；压型钢板闭口位置温度明显低于受火面底钢板，相同位置处再生混凝土组合板温度低于普通混凝土板；耐火极限受取代率的影响较小，再生混凝土组合板相对普通混凝土板耐火极限提高幅度在1.2%～9.2%,且远超过一级耐火极限90 min的要求；考虑钢板闭口部分受弯承载力贡献提出了耐火极限简化计算式，其可较好地预测组合板耐火极限。     

钢筋混凝土连续梁火灾下抗剪性能的试验研究

对8根足尺钢筋混凝土两跨连续梁和4根足尺钢筋混凝土简支梁进行了标准火灾试验,研究了钢筋混凝土连续梁高温下的抗剪性能,并与简支梁进行了对比,得到了连续梁混凝土及钢筋的温度变化、竖向挠度、轴向变形及最终破坏形态,分析了不同荷载比、剪跨比、混凝土保护层厚度、配箍率及受火工况对连续梁耐火极限的影响。结果表明:火灾下荷载比和混凝土保护层厚度对钢筋混凝土连续梁的抗剪性能影响显著。随着剪跨比和箍筋间距的减小,连续梁发生受剪破坏的耐火极限显著提高。与单跨受火工况相比,两跨同时受火的连续梁耐火极限降低。高温下连续梁由于发生了内力重分布,其抗剪性能优于简支梁。     

GFRP筋增强混凝土结构的抗火设计

通过火灾环境中混凝土内的温度场试验,以及火灾高温中玻璃纤维聚合物筋(GFRP筋)的力学性能和黏结性能试验,根据不同抗火等级对不同混凝土构件所要求的耐火极限时间,给出了GFRP筋增强混凝土结构的抗火设计方法.当抗火等级要求较高时,不宜采用GFRP筋增强混凝土结构.     

核安全相关钢板-混凝土组合剪力墙耐火性能试验研究

基于实际应用,对核安全相关钢板-混凝土组合剪力墙("SC剪力墙")结构耐火性能进行研究。通过8个试件的整体受火试验,分析墙体厚度、钢板厚度、栓钉间距、高厚比等因素对试件耐火极限的影响,得到"SC剪力墙"在两面受火时的温度场特点、高温下的失效机理,以及高温作用下"SC剪力墙"承载力、延性及耐火性能指标。试验结果表明:"SC剪力墙"具有良好耐火性能。     

钢框架结构整体抗火性能的数值分析

钢结构耐火性能差,其强度及弹性模量等基本力学指标在高温下急剧下降,一旦发生火灾往往导致结构倒塌。目前国内的钢结构设计主要采用试验的抗火设计方法,很难模拟荷载分布、大小等情况的影响,而通过数值计算进行抗火性能研究则可以合理的确定钢结构抗火极限及防火保护措施。本文考虑静力荷载和温度应力的影响,对钢框架进行整体抗火极限状态数值分析。     

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。     

三面受火的矩形钢管混凝土柱受力机理与耐火极限

受火边界作为研究结构构件抗火性能的基本前提条件之一,对结构构件抗火性能有着显著影响。已有钢管混凝土柱相关研究多假设其四面均匀受火,则针对实际结构中可能出现的三面受火这一情况,对矩形钢管混凝土柱进行抗火性能理论研究。分析了三面受火的矩形钢管混凝土柱温度场和耐火极限,以及高温全过程的构件受力机理,且与四面受火的矩形钢管混凝土柱进行了对比分析。研究表明:三面受火时构件截面的整体温度比四面受火时有显著降低,且三面受火时耐火极限高于四面受火;三面受火构件在高温全过程中轴向变形趋势与四面受火类似,而侧向变形可能会发生反转。     

不同受火方式下混凝土柱耐火性能的试验研究

通过5根高强混凝土柱和2根普通混凝土柱的足尺明火试验,考察了不同受火方式对混凝土柱破坏形态、轴向变形和耐火极限的影响。结果表明:(1)非四面受火柱的耐火极限较四面受火柱有很大提高,同时三面受火柱的耐火极限小于两面受火柱;(2)相同受火方式和相同轴压比下高强混凝土柱的耐火极限远低于普通混凝土柱;(3)相同受火方式下大轴压比普通混凝土柱的耐火极限可能小于中等轴压比的高强混凝土柱。在实际结构的抗火设计中,合理考虑受火方式、混凝土强度等级和轴压比的影响是十分必要的。     

火灾均匀温度场中正放四角锥网架结构临界温度研究

随着温度的升高,钢材的力学性能将会发生较大的变化。钢结构在均匀温度场达到承载能力极限状态时的临界温度是钢结构抗火性能的重要特征,而网架结构的临界温度主要受网架的几何特征、荷载比、构件稳定应力的影响。本文通过对不同参数条件下正放四角锥网架结构在均匀温度场中结构反应全过程分析,得到不同参数条件下正放四角锥网架结构的临界温度,为大空间建筑网架结构抗火设计实用方法提供理论依据。     

钢筋砼结构抗火性能研究现状与展望

火灾产生的高温可使建筑结构严重破坏甚至倒塌,为了保证建筑结构具有足够的抗火能力,必须进行建筑结构的抗火分析和设计。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、温度场计算、构件承载力计算以及建筑结构抗火性能应用软件研究等,并对今后的研究方向进行了展望。     

结构抗火分析中几个问题的评述

结构抗火分析是涉及到建筑结构和消防安全等方面的重点难点问题,火灾高温对结构有显著影响,火灾极易造成结构损伤、破坏甚至倒塌。随着我国基本建设的发展,结构抗火问题凸显其重要性。由于建筑物的规模和尺度都在不断加大,大幅度增加了火灾扑救的难度,这使得在加强结构抗火方面面临很多问题亟需解决。本文简要论述了近年来结构抗火研究的现状,指出了目前抗火研究尚需解决的关键技术难题,特别是基于实际火灾发展模型的结构抗火分析以及消防实践中高性能混凝土淬火效应导致的爆裂两个突出的问题。     

On the fire resistance of structural steel elements derived from standard fire tests or by calculation

Due to high costs, a fire resistance test of a load-bearing structural element is usually limited to one test specimen — in a few countries, to two test specimens. Accordingly, there are no possibilities of evaluating the test results statistically.For a single test specimen, the actual quality of the structural material represents a random sample from a wide variety. This applies also to the initial imperfections of the structural elements. In consequence of this, a standard fire resistance test is generally carried out on a test specimen with a load-bearing capacity which is greater — most often significantly greater — than the load-bearing capacity related to the characteristic values of the mechanical material strength and of the imperfections of the structural member. In current practice, no corrections of the test results with respect to this are made.In a conventional analytical design, a determination of the load-bearing capacity of a structure at room temperature conditions is based on the characteristics values of the strength and imperfections. Extended to a structural fire engineering design, this procedure will give an analytically determined fire resistance of a load-bearing structural element which is lower — normally essentially lower — than the corresponding value derived from a standard fire resistance test.Available methods for a simplified calculation of the temperature of fire exposed steel structures are, as a rule, based on the assumption of a uniformly distributed temperature structure at each time of fire exposure. The ECCS Recommendations for an analytical design of steel structures exposed to a standard fire follow this kind of approach. For certain types of steel structures, for example, beams with a slab on the upper flange, a considerable temperature variation arises over the cross section as well as in the longitudinal direction during a fire resistance test. A simplified, analytical method, which neglects this influence, gives a further underestimation of the fire resistance in relation to the corresponding result obtained in a standard fire resistance test.The described discrepancies between an analytical and an experimental determination of the fire resistance are further discussed and analysed in Sections 2 and 3, with particular reference to different types of steel structures. The discussion is focussed on the loading and restraint conditions, the scatter of material properties and geometrical imperfections, and the temperature variation over the structure or structural element. The discussion is summarized in Section 4 and alternative methods of correction are outlined briefly for obtaining an improved consistency between the analytical and the experimental approaches.In Section 5, one of these methods is further developed to a design basis which can be applied easily in practice. Principally, the method is characterized by a correction of the analytically determined load-bearing capacity, based on the characteristic value of the structural material properties, the characteristic value of the imperfections of the structure, and a uniformly distributed steel temperature across and along the structure. Two different sequences of the design procedure are dealt with, defined according to Figs. 10 and 11. The resultant correction factors, ? and κ, belonging to the respective sequences, are given by Figs. 8 and 12 for columns, isostatic beams, and hyperstatic beams. The straight line curves in Figs. 9 and 13 show corresponding, simplified relationships for the ? and κ factors.The derived method of correction must be characterized as an approximate approach. This is in consequence of the present state of knowledge, which does not allow a solution of high accuracy. The task to develop a correction procedure which leads to improved consistency between an analytically and an experimentally determined fire resistance, should also be seen in the context of the inadequate reproducibility of the standard fire resistance test.     

A practical approach for fire resistance design of extended end-plate joints

Although beam-to-column joints are known to have a very significant effect on the behaviour of steel frames in the event of fire, no specific approach for evaluating the behaviour of extended end-plate joints in fire has been proposed. In this paper, on the basis of the current Chinese Code for Design of Steel Structures [Chinese code for design of steel structures. 2002] and Technical Code on Fire Safety of Steel Building Structures [Chinese Technical code on fire safety of steel building structure. CECS, 2006], analysis is presented on the load-bearing capacity of extended end-plate joints in fire, by taking the mechanical properties of steel at elevated temperature into account. A practical approach for fire-resistance calculation and assessment of the joints is proposed, based on the load-bearing capacity of the components of joints at elevated temperatures including the bolt, extended end-plate, column flange and panel zone. Employing the practical approach, the critical temperatures of two extended end-plate joints are predicted. By comparison with the results measured from the tests, the effectiveness of this practical approach is verified.     

Rational design methodology for fire exposed load bearing structures

The state-of-art of reliability studies in the area of fire-exposed structures or structural members is illustrated, taking examples from published papers concerning load-bearing building structures of steel, reinforced concrete, and wood. In parallel, trends are described in the present development of rational structural fire design methods, principally adapted to modern loading and safety philosophy for the non-fire state. Statistically derived results are presented for fire-exposed, insulated steel structures in office buildings, giving the breakdown of the total variance in maximum steel temperature and load-bearing capacity into component variances as a function of the insulation characteristics. The safety index and probability of failure are compared numerically for different fire design procedures. The data presented are examples of the information which is required as input in a qualified systems analysis of fire exposed load-bearing structures.     

四边简支现浇混凝土空心楼盖二次抗火性能试验研究

为探究火灾后采用聚合物砂浆加固修复混凝土空心楼盖二次火灾下的抗火性能,对四边简支混凝土组合塑料模盒空心楼盖进行两次火灾试验。介绍了试验空心楼盖第一次受火试验及火灾后构件修复情况,重点介绍了加固修复后空心楼盖第二次火灾试验,描述了试验空心楼盖在两次受火下的破坏特征、变形和温度场分布规律,并进行分析和对比。研究结果表明:采用聚合物砂浆修复的空心楼盖在二次火灾作用下,第一次火灾受损较为严重的部位易产生爆裂脱落,从而降低了耐火极限;二次受火下楼盖内混凝土的温度峰值高于一次受火,且距离板底越近,两次火灾作用中温度峰值差值越大;试件在两次火灾作用下跨中处最大竖向位移基本相同,第二次受火作用后的残余位移小于第一次;采用聚合物砂浆对火灾后的空心楼盖进行修复,修复后的楼盖仍具有一定的抗火性能。     

单面受火的方钢管约束钢筋再生混凝土柱耐火极限

为研究单面受火的方钢管约束钢筋再生混凝土柱的耐火极限,采用有限元软件ABAQUS建立了ISO-834标准火灾作用下单面受火的方钢管约束钢筋再生混凝土柱有限元模型,相关试验验证之后、分析了截面温度场和应力场的变化规律。在此基础上分析取代率、混凝土强度、荷载比、含钢率、荷载偏心率、荷载角、配筋率、截面尺寸和钢材强度等参数对构件耐火极限的影响规律。结果表明：荷载偏心率和荷载角对构件耐火极限影响较为复杂,当荷载角为180°时,荷载偏心率由0.2增加到0.4,构件耐火极限增加11.2%;当荷载偏心率为0.8时,荷载角由0°增到90°,构件耐火极限降低32.2%;荷载比和截面尺寸对构件耐火极限影响明显,当含钢率为5.33%时,荷载比由0.4增到0.5,其耐火极限降低37.1％;当钢材强度为Q345时,截面尺寸由200mm增到300mm时,构件耐火极限增加66.73%。基于上述规律并结合计算结果给出了单面受火的方钢管约束钢筋再生混凝土柱的耐火极限简化计算式,可为该类柱抗火设计提供参考。