预应力钢结构抗火研究现状

预应力技术与现代钢结构的完美结合,形成了全新的现代预应力空间钢结构体系,这种体系完美地解决了大跨空间建筑对结构体系的要求,在世界各地的体育场馆、展览馆等建筑物中得到广泛应用。但该类建筑功能复杂,火灾隐患大,火灾时更易引起人员伤亡,且火灾作用下钢材力学性能退化、预应力筋松弛,造成正常使用荷载下建筑结构的损伤、破坏甚至倒塌,因此对预应力钢结构进行抗火性能的研究尤为重要。为此系统论述了预应力钢结构抗火研究的重要性和研究现状,同时指出了其中存在的某些未完善的问题和进一步的研究方向。     

型钢混凝土框架结构耐火性能有限元分析

为了研究型钢混凝土框架整体结构的耐火性能,为其抗火设计提供参考,采用受火楼层建立精细化有限元计算模型、非受火楼层建立梁单元计算模型的方法,建立了型钢混凝土框架整体结构的耐火性能计算模型。考虑火灾位置、荷载分布形式、柱轴压比等参数的影响,对火灾下型钢混凝土框架整体结构的变形规律、承载机制、破坏形态以及耐火极限进行参数分析。分析结果表明：火灾下框架结构出现了整体破坏和局部破坏两种典型的破坏形态,受火构件受到的约束作用对其耐火性能有较大的影响;在局部破坏形态中,由于受热膨胀,火灾下框架梁首先出现了较大的轴压力,受火框架梁处于压弯受力状态;之后,框架梁出现了悬链线效应,轴力对框架梁的受力状态有较大影响;在整体破坏形态中,根据轴压比及荷载分布形式的不同,框架出现了中柱破坏和边柱破坏两种典型破坏形态,同时,随楼层受火位置的升高,柱的轴压比减小,框架结构的耐火极限增加。     

火灾作用下空间桁架结构响应分析

针对钢结构建筑耐火性能差的弱点,建立了空间桁架屋顶结构有限元计算模型和空间桁架结构随时间的变化模型,分析了受火区域构件的温度场,以及火灾荷载下空间桁架结构的响应,并提出改进措施。     

Response of steel beam–columns exposed to fire

Steel beams when exposed to fire develop significant restraint forces and often behave as beam–columns. The response of such restrained steel beams under fire depends on many factors including fire scenario, load level, degree of restraint at the supports, and high-temperature properties of steel. A set of numerical studies, using finite element computer program ANSYS, is carried out to study the fire response of steel beam–columns under realistic fire, load and restraint scenarios. The finite element model is validated against experimental data, and the importance of high-temperature creep on the fire response of steel beam–columns is illustrated. The validated model is used to carry out a set of parametric studies. Results from the parametric studies indicate that fire scenario, load level, degree of end-restraint and high-temperature creep have significant influence on the behavior of beams under fire conditions. The type of fire scenario plays a critical role in determining the fire response of the laterally-unrestrained steel beam within a space subframe. Increased load level leads to higher catenary forces resulting in lower fire resistance. Rotational restraint enhances the fire resistance of a laterally-unrestrained steel beam, while the axial restraint has detrimental effect on fire resistance.     

Nonlinear behaviour of unprotected composite slim floor steel beams exposed to different fire conditions

An efficient nonlinear 3D finite element model has been developed to investigate the structural performance of composite slim floor steel beams with deep profiled steel decking under fire conditions. The composite steel beams were unprotected simply supported with different cross-sectional dimensions, structural steel sections, load ratios during fire and were subjected to different fire scenarios. The nonlinear material properties of steel, composite slim concrete floor and reinforcement bars were incorporated in the model at ambient and elevated temperatures. The interface between the structural steel section and composite slim concrete floor was also considered, allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the composite beam. Furthermore the thermal properties of the interface were included in the finite element analysis. The finite element model has been validated against published fire tests on unprotected composite slim floor steel beams. The time–temperature relationships, deformed shapes at failure, time–vertical displacement relationships, failure modes and fire resistances of the composite steel beams were evaluated by the finite element model. Comparisons between predicted behaviour and that recorded in fire tests have shown that the finite element model can accurately predict the behaviour of the composite steel beams under fire conditions. Furthermore, the variables that influence the fire resistance and behaviour of the unprotected composite slim floor steel beams, comprising different load ratios during fire, cross-section geometries, beam length and fire scenarios, were investigated in parametric studies. It is shown that the failure of the composite beams under fire conditions occurred for the standard fire curve, but did not occur for the natural fires. The use of high strength structural steel considerably limited the vertical displacements after fire exposure. It is also shown that presence of additional top reinforcement mesh is necessary for composite beams exposed to short hot natural fires. The fire resistances of the composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 predictions are generally conservative for the design of composite slim floor steel beams heated using different fire scenarios.     

基于整体的大空间钢结构性能化防火设计方法研究

大尺度空间钢结构建筑的飞速发展为结构抗火设计带来了新的挑战。在分析现有规范和性能化结构抗火设计不足的基础上,基于性能化设计的思想,综合多学科知识和研究成果,采用火灾模拟计算和结构分析耦合集成的技术方法,建立基于整体的大空间钢结构性能化抗火设计方法,给出具体流程,最后通过工程实例说明该方法的实际应用。研究表明,对于大空间结构而言,传统抗火分析方法与真实火灾下的结构特性存在较大的差异,且火灾温度场的非均匀性对结构体系的抗火性能有着重要的影响。本课题的研究在理论分析的基础上为大型钢结构建筑性能化结构抗火设计和分析提出了系统化技术流程,可为我国大空间结构的抗火设计提供有益参考,具有广阔应用前景。     

大跨度空间结构抗火研究进展

对国内外近年来关于大跨度空间结构的抗火研究进行了系统的综述与分析.论述了大空间建筑火灾模型和温度场的研究内容,介绍了大空间建筑火灾中钢构件升温的计算方法,说明了大跨度空间结构所用材料的抗火性能,详细阐述了火灾高温作用下一些大跨度空间结构体系的抗火性能,并对目前性能化的抗火设计方法及其在工程中的应用做了介绍与总结,最后指出了尚存在的问题及需要进一步研究的工作.     

Finite element analysis of concrete-filled circular steel tubular columns subjected to post-earthquake fire

为研究圆钢管混凝土柱经历地震损伤后的耐火性能,选取了合理的地震损伤指数及材料本构模型,采用有限元分析软件ABAQUS,对钢管混凝土柱在往复荷载和火灾等不同工况下的试验进行了数值模拟验证。在验证模型可靠性的基础上,利用ABAQUS中的数据传递功能,建立了震损后圆钢管混凝土柱耐火极限有限元计算模型。以圆钢管混凝土典型轴心受压柱为分析对象,对其先后经历地震和火灾作用下的破坏形态、损伤机理进行了分析,研究了损伤指数对圆钢管混凝土柱震后耐火极限的影响。结果表明：震损后圆钢管混凝土柱在高温下的破坏形态是在前期地震损伤基础上的发展和蔓延;地震损伤指数是影响圆钢管混凝土柱震后耐火极限的重要参数,随着地震损伤指数增大,圆钢管混凝土柱的耐火极限有所减小。     

钢框架结构抗火性能的试验研究

本文介绍四次不同水平荷载作用下,单层单跨钢框架结构的抗火试验,试件由特制的煤气炉进行加热升温,试验结果和理论分析结果吻合良好,文章最后提出了几点结论,供钢结构抗火设计参考.     

预测火灾下钢构件温度的简单方法

为评价钢结构构件的抗火性能,需要了解构件横截面的温度。给出了一种预测火灾下有外保护层的钢构件截面温度的简单方法。利用标准火灾条件下的简化假设得到该方法,并推广到设计火灾情况。该方法适用于有保护层和没有保护层的型钢构件。将预测温度与ANSYS有限元分析结果进行比较,验证了该方法的有效性。此外,该方法的预测结果也与"最佳拟合"法的预测温度进行了比较。与试验结果、有限元计算结果和"最佳拟合"法预测结果的比较表明,所提出的简化方法能够较好地预测各种火灾下型钢构件的热梯度和温度历史。该方法简单明了,适合设计时使用。     

钢结构的抗火研究概述

由于钢结构的耐火性差,其抗火研究一直是建筑安全领域的研究重点。参考国内外资料,论述了钢结构抗火研究的意义,介绍了建筑室内火灾的发展和温度的变化,以及火灾中钢结构的温度响应和结构响应,概述了钢结构抗火研究的主要方法,同时指出目前研究中尚存在的不足和进一步研究的方向。     

钢结构抗火安全研究现状与发展趋势

火灾引起的高温严重降低建筑钢材的强度和刚度,从而造成钢结构损伤、严重破坏甚至倒塌。20世纪90年代人们开始重视钢结构抗火理论研究,2001年美国“9·11”事件引起了世界各国对钢结构抗火问题的高度关注。结构抗火学科经过几十年的发展,已形成系统的抗火理论和设计方法,文章介绍火灾引起钢结构破坏的原因,论述结构抗火设计原则的发展过程,归纳近年来钢结构抗火研究的重大进展,指出钢结构抗火的重要发展趋势,供有关研究者参考。     

1截面形式对高温下钢管混凝土柱轴向加载性能的影响

钢管混凝土柱能够最大限度地发挥材料特性,现广泛用于建筑结构中。钢管混凝土柱承载能力高,能量吸收能力强,结构的抗火性能好。描述了含4种截面形式的一系列钢管混凝土柱在标准火下的抗火性能。按照以下方式将钢管混凝土柱分为三组:室温下截面强度相等、钢管截面面积相等、混凝土截面面积相等。采用ABAQUS软件分析组合柱的温度分布、临界温度和过火时间等情况。基于典型参数的分析和对比,讨论了不同截面形式钢管混凝土柱的温度分布和抗火性能。结果显示,圆截面钢管混凝土柱抗火性能最佳,接下来是椭圆截面、正方形截面和矩形截面。在该研究的基础上,给出了高温下钢管混凝土柱的简化设计方程。     

Degradation of Out-of-plane Initial Stiffness of Steel-concrete Walls Exposed to Fire

Steel-concrete (SC) walls, as a main lateral resisting system in nuclear power plants, have serious fire resistance problem because of their exposed steel faceplates. The out-of-plane stiffness of SC walls will degrade when exposed to fire, which has significant influence on the mechanical performance of the composite walls and even the whole structure. In this paper, a finiteelement (FE) model was developed to simulate thermo-mechanical coupling behavior of SC walls exposed to fire. One conducted ISO-834 standard fire test and two reported thermal and mechanical loading tests were assembled to verify the developed FE model. Based on the validated FE model, numerical experiments of 15 SC walls in fire exposure durations of 0~3 h were conducted to investigate the effect of steel arrangement and geometrical size on the out-of-plane initial stiffness of SC walls under elevated temperatures. Numerical results indicate that the out-of-plane initial stiffness of SC walls under ambient temperature is mainly influenced by steel faceplate thickness and section depth, while the initial stiffness degradation under elevated temperature is mainly influenced by fire exposure duration or surface temperature of exposed steel faceplate. Then, two equations were proposed to predict the out-of-plane initial stiffness of SC walls exposed to fire. The predicted results agree well with the test and numerical results, which demonstrates that the proposed equations can be used to estimate the damage of SC walls in fire.     

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。     

大跨度钢桁架吊装过程分析

随着我国社会经济的高速发展,大跨度空间结构得到了迅速发展,广泛应用于机场、展览馆、体育馆等大型公共建筑中。但是大跨度空间钢结构的施工安装技术,仍然是建筑技术研究的重要课题之一。结合中航上海民用大场基地205号技术综合楼钢桁架整体吊装工程,对吊装过程中涉及的吊点布置以及钢桁架强度、刚度和稳定性等问题进行了综合分析,确定了合理的吊点数量与布置方式,选择了合理的吊装机械性能参数,提出了合理的绑扎宽度,为吊装过程提供理论依据,也为相关钢结构安装提供参考资料。     

高层塔式钢结构性能化防火安全分析

由于采用大空间的建筑布局以及可燃物的特殊性,现有规范方法难以满足河南省新广播电视塔防火设计安全性与经济性要求。基于性能化设计思想对该工程全景画馆钢结构体系的抗火安全性进行了评估。确定结构抗火性能目标,对结构整体在可能最不利火灾场景下的力学性能进行分析,根据结构的受火性能是否满足抗火性能目标来评估结构的抗火安全性及需要采取的防火保护措施。在此基础上对整个塔体结构的安全性进行了分析,其成果可为国内外高层钢结构的整体抗火分析提供借鉴和参考。     

Influence of steel ratio on fire resistance of concrete-filled square steel tubular columns with internal profiled steel

采用ABAQUS有限元软件,建立了火灾作用下内配型钢方钢管混凝土轴压柱耐火性能的有限元模型,验证了有限元模型的可靠性。在保证钢材总含钢率不变的前提下,对钢管和内配型钢进行分配,对比分析了两种截面形式柱常温承载力和耐火极限。对钢管含钢率、型钢含钢率以及钢材材料强度进行了分析,并对不同截面总含钢率下钢管含钢率分配比例对耐火极限的影响进行了计算和分析。结果表明：保持总含钢率不变,将钢管中部分钢材以型钢的形式置于混凝土中,常温下承载力略有降低,但火灾下耐火极限提高甚为显著;当钢管含钢率占截面总含钢率的50%~60%时,常温下承载力和火灾下耐火极限均能得到充分的发挥。     

Shape effect on the behaviour of axially loaded concrete filled steel tubular stub columns at elevated temperature

Concrete filled steel tubular columns have been extensively used in modern construction owing to that they utilise the most favourable properties of both constituent materials. It has been recognized that concrete filled tubular columns provide excellent structural properties such as high load bearing capacity, ductility, large energy-absorption capacity and good structural fire behaviour. This paper presents the structural fire behaviour of a series of concrete filled steel tubular stub columns with four typical column sectional shapes in standard fire. The selected concrete filled steel tube stub columns are divided into three groups by equal section strength at ambient temperature, equal steel cross sectional areas and equal concrete core cross sectional areas. The temperature distribution, critical temperature and fire exposing time etc. of selected composite columns are extracted by numerical simulations using commercial FE package ABAQUS. Based on the analysis and comparison of typical parameters, the effect of column sectional shapes on member temperature distribution and structural fire behaviour are discussed. It shows concrete steel tubular column with circular section possesses the best structural fire behaviour, followed by columns with elliptical, square and rectangular sections. Based on this research study, a simplified equation for the design of concrete filled columns at elevated temperature is proposed.     

Finite element modelling of steel fin plate connections in fire

Recent structural collapses caused by fire have focused attention on research concerning fire safety in building design. Steel connections are an important component of any structural steel building, as they provide links between the principal structural members. The evaluation of the performance of steel connections at elevated temperatures has been a topic of several research programmes in the last few years. Determining the behaviour, available strength and stiffness of moment connections in fire conditions has been a dominant theme in these research works; however very little information on the behaviour of simple shear connections in fire conditions has been disseminated. Fin plate shear connections are easy to fabricate and install; as a result, they have gained popularity with fabricators because of their economy. In this research, the robustness of simple fin plate beam-to-column connections is being investigated under catenary tension from highly deflected beams in fire. A highly detailed three-dimensional (3-D) finite element (FE) model has been created using the ABAQUS software. This is a complex model accounting for material and geometric non-linearity, large deformation and contact behaviour. Contact is critical to model the shear behaviour of the joint, and contact elements have been used both at the bolt–hole interface and also at the surface between the web of the beam and the fin plate, taking into consideration friction between the surfaces. The connection model has been analysed through the elastic and plastic ranges up to failure. Bolt shear and bending, and plate and web bearing have been observed as failure modes. A comparison between available experimental data at ambient and elevated temperatures and other analytical results shows that the model has a high level of accuracy. When the connection model was extended to include an attached beam, it was found that it eventually experiences large tensile force when exposed to fire.