大跨钢结构抗火设计方法

介绍大跨钢结构构件及整体结构的抗火设计方法。依据工程实例,设定火灾场景,采用数值模拟的方法确定火灾温度场,通过考虑对流和辐射传热确定结构构件的温度。考虑火灾和荷载的组合效应对构件承载能力进行验算,分析整体钢结构的应力、位移变化,得出耐火时间,指导大跨钢结构构件和整体结构的抗火设计。     

钢-混凝土组合结构抗火性能研究与应用

钢-混凝土组合结构抗火性能研究是当前的研究热点之一,国内外学者对此展开大量试验研究和理论分析。通过介绍国内外研究者在组合板、组合梁、组合柱等构件以及结构节点和结构体系抗火性能方面研究概况,分析了我国现有防火设计规范的特点以及工程应用情况,指出现有研究的不足,对组合结构抗火研究领域在高温材料热-力耦合本构关系、计算理论、数值火灾试验和设计方法等方面需进一步研究的工作进行了展望。文中指出,建立考虑升降温、多轴应力状态、不同加卸载路径的钢材和混凝土热-力耦合本构关系,建立基于整体性能、考虑升降温全过程的结构抗火分析理论,建立整体结构数值火灾试验方法,提出“三水准”结构抗火设计与灾后结构损伤评估原则以及基于时变可靠度和结构整体性能的组合结构抗火设计方法是钢-混凝土组合结构抗火性能研究的关键科学问题。表2参119     

基于多尺度建模的震损RC框架抗火混合模拟

基于构件的震后火灾试验无法全面真实反映整体结构历经地震损伤后局部构件的受火性能,采用ABAQUS软件建立不同损伤组合下的钢混框架有限元模型,并将多尺度建模方法与抗火混合模拟相结合,研究不同建模方式的计算结果差异、不同损伤组合对结构耐火极限的影响,以及抗火混合模拟评估结构震后火灾性能的适用性。结论表明：相对微观单元模型,多尺度单元模型的计算时间在裂缝损伤下和裂缝与剥落共同作用损伤下分别缩短68%和61%,裂缝与剥落共同作用损伤较裂缝损伤耐火极限降低22%,由于考虑了边界条件的变化,抗火混合模拟能够通过局部构件试验反映整体结构的震后抗火性能。     

海口双子塔-南塔钢结构抗火设计

海口双子塔-南塔结构体系外侧为巨型钢管混凝土柱+钢支撑框架,内部为钢板混凝土核心筒,二者之间为钢结构组合楼盖,需进行抗火设计。采用临界温度法对结构进行抗火设计,基于抗火设计结果建立热-固耦合整体结构模型,继而进行抗火灾连续倒塌分析。分析时考虑了高温下构件材料的刚度、屈服强度等折减以及构件的温度应力,同时对耐火极限后的构件损坏进行了评价。结果表明,采用临界温度法抗火设计以及基于整体结构的火灾全过程分析,基本可实现建筑结构在火灾时的抗连续倒塌设计目标,其中大跨组合钢次梁为防连续倒塌薄弱构件,转换梁及钢结构节点需进行防火加强。     

型钢-混凝土组合结构节点抗火性能综述

论述了节点抗火设计的必要性和重要性,在综述了近年来国内外建筑结构抗火研究现状的基础上对组合结构节点抗火研究进行了归纳总结,对未来型钢-混凝土组合结构节点抗火性能研究方向提出了一些建议。     

压型钢板-混凝土组合楼板抗火性能非线性分析

压型钢板-混凝土组合楼板是目前广泛运用的一种新型结构构件,但由于缺乏对组合楼板抗火性能的研究,现有设计方法并没有充分发挥材料的性能。本文在建立室内火灾传热模型基础上,在空间上运用有限单元法和在时间上运用有限差分的混合解法,编制计算程序解算出火灾下组合楼板在不同时刻的温度场,进而利用钢筋混凝土非线性有限单元法,对多种工况下组合楼板的抗火性能进行了分析,为组合楼板的抗火设计及研究提供了一定的基础。     

新建昆明国际机场航站楼屋顶网架结构的抗火研究与设计

基于性能化方法对新建昆明国际机场航站楼屋顶网架结构进行了结构抗火设计.对大型网架结构整体抗火设计问题进行了探讨.推荐了一种钢结构抗火性能化设计的设计流程.介绍了抗火性能化设计中高大空间火灾下钢构件升温的实用计算公式.讨论大型网架结构抗火整体分析中的温度加载模型.推荐了适用于钢结构抗火整体分析中的荷载组合方法.     

高温下钢筋混凝土内部温度场数值模拟

针对高温下钢筋混凝土构件导热的非线性瞬态特点,全面考虑其热工参数和质量热容参数的变化时序性,把传热学理论与计算机数值模拟技术相结合,利用ANSYS热分析功能,模拟高温(火灾)作用下混凝土构件内部温度场的变化,应用瞬态温度场仿真程序对四面受火矩形截面柱和T形截面梁温度场进行了数值模拟,模拟结果较试验结果偏大的原为模拟未考虑结构构件实际火灾环境的散热。算例模拟表明,模拟结果与文献给出的试验结果图形曲线走向一致,验证了计算机数值模拟结果分析的适用性与正确性,为混凝土结构构件抗火分析提供了计算辅助手段与理论依据。     

广义组合结构及其发展展望

本文对组合结构的发展历史和当前的研究及应用现状进行了综述。根据钢-混凝土组合结构的发展趋势和新材料的不断出现和应用,本文提出了广义组合结构的概念。广义组合结构不仅包括钢和混凝土的组合,而且包括更多新材料的组合,是对传统钢-混凝土组合结构的发展。广义组合结构将不同的材料或构件组合在一起共同工作,在设计时将各组成材料和构件的结构性能进行整体考虑,以最有效地发挥各种材料和构件的优势。此外,还对新型组合构件的研发、组合结构体系的创新、组合加固技术的发展以及组合结构在其他领域内的研究和应用进行了展望。     

真型输电塔无填板十字型组合角钢构件的受力性能研究

结合工程实践应用,提出一种无填板十字型组合角钢构件型式,根据设计最大荷载工况,依据试验规范DL/T 899-2012,通过真型塔试验和数值模拟分析论证了无填板十字型组合角钢构件在输电铁塔结构中的适用性,从构件的弹性屈曲模态和稳定承载力两个方面进行了对比分析.研究表明:无填板十字型组合角钢构件的弹性屈曲模态与传统有填板十...     

Structural behaviour of composite slim floor frames in fire conditions

The structural behaviour of the composite slim floor frame as a whole in fire conditions has been investigated. Both the deformation behaviour of the structural members and the mechanical interaction between the members were studied. The additional lateral deformation of the side-column caused by the thermal expansion and the catenary action in the beam in the different fire phase was highlighted. The moment variation in the head of the columns during fire and the variation of the axial force in the heated beam were also investigated. A comparison between the deformation behaviour of the heated beam in the plane frame and the spatial frame indicated the excellent effects of the composite floor slab on the stability of the frame structures in fire.     

钢筋网水泥复合砂浆薄层的耐火性能试验研究

使用无机材料钢筋网水泥复合砂浆薄层加固钢筋混凝土构件是一种较新的加固方法,它与一些需使用有机结构胶的加固方法相比具有更好的耐火性能。对用这种方法加固的钢筋混凝土试块进行了高温下耐火性能的试验研究。试验包括5个用不同厚度钢筋网水泥复合砂浆薄层及外抹砂浆加固的试块和1个用钢筋网普通水泥砂浆加固的对比试块,研究了试块加固后在高温下的耐火极限和内部温度场分布情况。试验结果表明,与普通水泥砂浆相比,使用这种水泥复合砂浆材料的加固层可以提高试块的耐火极限,同时,钢筋网保护层厚度和外抹砂浆层对耐火极限和温度场的影响也是很明显的。     

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.     

火灾下钢结构楼板的薄膜作用

通过对真实火灾中的足尺火灾试验和观察显示，合组合楼板和承载钢梁的建筑物的结构承载力比现行杭大设计方法的建议值高出许多。因此规范中规定所有承载钢梁都要添加被动防火保护是不必要的。现行设计方法和实际结构性能之间产生这种差异是由于设计方法中忽略了楼板的薄膜作用。本根据国外有关资料给出了几种简单计算方法，允许在钢结构杭大设计中考虑楼板的薄膜作用。从而可以更精确地评估火灾下建筑物的真实承载能力，在给定的耐火时间内能减少相当数量钢梁的防火保护。     

Experimental behaviour of composite slabs during the heating and cooling fire stages

Most theoretical and experimental research investigating the effect of fire on structures has previously concentrated only on the structural behaviour during the heating stages of the fire, partly due to the fact that internationally accepted standard fire tests only consider this stage of the fire. Evidence from real fires in real buildings has highlighted that the cooling phase of a fire is equally important and it is possible for structures to fail during this stage of the fire even though they have survived the heating stage up to a maximum fire temperature. This paper provides an insight into the behaviour of composite slabs under different fire scenarios considering both the heating and cooling phase of the fire. Extensive test data is presented which shows the redistribution of moments and strains in the deck and steel mesh, together with displacements during the full duration of the fire. The results show that the behaviour of composite slabs is dependent on the heating rate, the maximum temperature reached and the cooling rate. In terms of overall performance, displacements and the temperature on the non-fire side of the slab are important. For the tests presented in this paper it was shown that one fire scenario resulted in the maximum displacement but another fire scenario resulted in the maximum temperature on the unexposed face. In addition the maximum temperature of the unexposed side of the slab and the mesh reinforcement within the slab occurring during the cooling stages of the fire. This highlights the fact that the performance of structures must be checked in design under a range of possible fire scenarios, which must include both the heating and cooling stages of a fire.     

Numerical modelling of the structural fire behaviour of composite buildings

This paper describes numerical models constructed to simulate the response of composite steel/concrete building floors under fire conditions. In particular, this study deals with two of the fire tests recently undertaken on a full-scale multi-storey building at Cardington, UK. The analysis is carried out using a structural analysis program which accounts for both geometric and material nonlinearities, and which includes temperature-dependent constitutive models for steel and concrete materials. The approaches used to represent the various structural details are discussed, and the procedure employed for incorporating the experimentally measured temperature profiles and histories is outlined. For the two tests considered in this investigation, the numerical results are in general agreement with the experimental data, particularly in terms of the magnitude of vertical deformations induced in the floors at elevated temperatures. Close examination of the numerical and experimental findings provides an insight into the complex interactions that occur in the structure at elevated temperatures. Most significantly, the influence of the restraint to thermal expansion of the heated floor area, which is provided by the surrounding parts of the structure, is shown to be of paramount importance. The increasing confidence that can be placed in numerical models as well as the improved understanding of the structural fire response may be used in developing more realistic and cost-effective design methods which are based on the actual structural response rather than that of isolated members.     

温度梯度下计算钢梁弯曲承载力计算的适应因子

适应因子提供了估计温度梯度下钢梁弯曲承载力的简单方法。欧洲的钢结构设计规范中介绍了火灾情况适应因子的应用。由于其他结构或非结构构件进行局部防火保护时,钢或混凝土组合梁内通常会出现温度梯度。当无保护的钢截面存在任何温度梯度时,欧洲规范规定适应因子取值0.7,在同样火灾情况下对有保护的梁适应因子取值0.85,这些值被用于提高钢梁的计算弯曲承载力,此时假定横截面温度均匀。有关适应因子的文献很少。本文对在火灾中,按照欧规对钢梁在不均匀温度场中适应因子的设计取值进行验算。通过各种温度梯度情况的数值计算,对其在钢或混凝土组合梁结构一般情况下的应用进行了研究。并对规范所采纳的适应因子值的稳定性进行讨论并给出了推荐值。     

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。     

Adaptation factor for moment capacity calculation of steel beams subject to temperature gradient

Adaptation factors provide a simple means to estimate the moment capacity of a steel beam subject to temperature gradient. The use of adaptation factors is introduced in Eurocode for structural steel design under fire conditions. Temperature gradients arise in a steel/concrete composite beam usually as a result of the partial protection from fire by another structural or non-structural member. For a bare steel section subject to any temperature gradient, a value of 0.7 is stipulated for the adaptation factor in the Eurocode. A value of 0.85 is stipulated for protected beam under the same fire situation. These values are used to increase the steel beam’s calculated moment capacity which is based on an assumed uniform temperature of the cross-section. Literature on the use of the adaptation factors is scarce. In this paper, the value of the adaptation factor being adopted by the Eurocode for design of steel beam in fire with non-uniform temperature distribution is examined. The use of this value in the general cases of steel/concrete composite beam construction is studied by carrying out numerical computations for various temperature gradient cases. The suitability of the adaptation factor value adopted by the code is discussed and recommendations given.     

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.