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。     

复杂空间钢结构整体性防火分析的系统方法研究

复杂空间钢结构建筑的飞速发展为结构防火分析和设计带来了新的挑战。在分析现有规范和性能化设计方法中结构防火设计不足的基础上,基于火灾科学、结构工程、计算机模拟等多个学科领域的知识和研究成果,立足于复杂空间建筑的整体防火性能模拟与分析的理论研究和实际应用,建立空间整体结构火灾-结构耦合分析模型和系统集成方法,提出复杂空间结构整体性防火分析的系统分析模型,并进行实例研究。该系统分析模型综合考虑实际火灾的发展蔓延过程以及火灾对结构体系的影响,研究建筑火灾中火场状况与空间结构体系之间的相互关系,对大空间建筑在各种火灾场景下的结构反应进行仿真模拟,从而进行整体性系统化的分析和评估。本课题的研究在理论分析的基础上为结构整体防火分析提出了新的手段和思路,可为我国建筑防火研究和建筑防火设计、消防救援、应急预案制定等工程实际应用提供有益的参考。     

Study on nominal values of mechanical properties of high strength steel at elevated temperature and after fire exposure

高强钢高温下和高温后的力学性能是进行高强钢结构抗火设计和火灾后评估的重要基础。我国GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EC3中针对普通低碳钢提出了高温下屈服强度和弹性模量计算公式，但其不适用于高强钢。国内外学者对高温下和高温后高强钢力学性能已开展了一系列试验研究，但由于钢材强度等级、试验设备、加热速率和加载制度等影响，导致试验结果离散性较大，不能应用于实际工程中。同时不同学者提出的力学性能指标计算式各不相同，均不具有普遍适用性。采用数理统计中t分布与置信区间的方法对高强钢高温下和高温后力学性能试验数据进行统计分析，得到不同温度下力学性能指标具有95%保证率的标准值，拟合出高强钢高温下和高温后力学性能指标的计算式，并与GB 51249—2017和欧洲规范EC3预测结果进行对比。结果表明：自然冷却和浸水冷却条件下，高强钢高温后屈服强度发生明显下降的转折点分别是600℃和 500℃；高温下高强钢的屈服强度折减系数低于普通结构钢；高强钢弹性模量折减系数在作用温度小于600℃时低于普通结构钢的，而在温度大于600℃时高于普通结构钢的。     

高强钢高温下和高温后力学性能指标的标准值研究

高强钢高温下和高温后的力学性能是进行高强钢结构抗火设计和火灾后评估的重要基础。我国GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EC3中针对普通低碳钢提出了高温下屈服强度和弹性模量计算公式,但其不适用于高强钢。国内外学者对高温下和高温后高强钢力学性能已开展了一系列试验研究,但由于钢材强度等级、试验设备、加热速率和加载制度等影响,导致试验结果离散性较大,不能应用于实际工程中。同时不同学者提出的力学性能指标计算式各不相同,均不具有普遍适用性。采用数理统计中t分布与置信区间的方法对高强钢高温下和高温后力学性能试验数据进行统计分析,得到不同温度下力学性能指标具有95%保证率的标准值,拟合出高强钢高温下和高温后力学性能指标的计算式,并与GB 51249—2017和欧洲规范EC3预测结果进行对比。结果表明：自然冷却和浸水冷却条件下,高强钢高温后屈服强度发生明显下降的转折点分别是600℃和 500℃;高温下高强钢的屈服强度折减系数低于普通结构钢;高强钢弹性模量折减系数在作用温度小于600℃时低于普通结构钢的,而在温度大于600℃时高于普通结构钢的。     

Experimental investigation of post-fire mechanical properties of cold-formed steels

Cold-formed steel members are widely used in residential, industrial and commercial buildings as primary load-bearing elements. During fire events, they will be exposed to elevated temperatures. If the general appearance of the structure is satisfactory after a fire event then the question that has to be answered is how the load bearing capacity of cold-formed steel members in these buildings has been affected. Hence after such fire events there is a need to evaluate the residual strength of these members. However, the post-fire behaviour of cold-formed steel members has not been investigated in the past. This means conservative decisions are likely to be made in relation to fire exposed cold-formed steel buildings. Therefore an experimental study was undertaken to investigate the post-fire mechanical properties of cold-formed steels. Tensile coupons taken from cold-formed steel sheets of three different steel grades and thicknesses were exposed to different elevated temperatures up to 800 °C, and were then allowed to cool down to ambient temperature before they were tested to failure. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield stress, Young׳s modulus, ultimate strength and ductility). It was found that the post-fire mechanical properties of cold-formed steels are reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 300 °C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of cold-formed steels. Such post-fire mechanical property assessments allow structural and fire engineers to make an accurate prediction of the safety of fire exposed cold-formed steel buildings. This paper presents the details of this experimental study and the results of post-fire mechanical properties of cold-formed steels. It also includes the results of a post-fire evaluation of cold-formed steel walls.     

火灾降温阶段型钢混凝土框架结构受力性能研究

在火灾降温阶段,结构构件的截面部分区域升温的同时,也有区域在降温,结构受力性能较为复杂,建筑结构更易发生倒塌破坏。为研究火灾降温阶段型钢混凝土框架结构的受力性能,通过已有火灾升降温条件下型钢混凝土框架及柱的受力性能试验,得到了构件截面的温度-时间关系曲线、结构变形-时间关系曲线,以及升降温过程中框架及柱的破坏形态。同时,采用有限元模型对升降温过程中型钢混凝土框架及柱的受力性能进行分析。结果表明：在火灾降温阶段,构件截面的升温区和降温区的范围在逐渐变化,截面的应力也随之发生变化。在此阶段,构件截面内部温度升高导致材料强度降低,截面外部处于降温区域的材料强度进一步降低,截面内外温差导致截面周围出现拉应力。上述因素的共同作用导致结构在火灾降温阶段发生破坏。相较于受火前,结构温度降至室温时结构的刚度降低、变形增加。     

Mechanical performance of steel reinforced concrete frame structures during fire including a cooling phase

在火灾降温阶段，结构构件的截面部分区域升温的同时，也有区域在降温，结构受力性能较为复杂，建筑结构更易发生倒塌破坏。为研究火灾降温阶段型钢混凝土框架结构的受力性能，通过已有火灾升降温条件下型钢混凝土框架及柱的受力性能试验，得到了构件截面的温度-时间关系曲线、结构变形-时间关系曲线，以及升降温过程中框架及柱的破坏形态。同时，采用有限元模型对升降温过程中型钢混凝土框架及柱的受力性能进行分析。结果表明：在火灾降温阶段，构件截面的升温区和降温区的范围在逐渐变化，截面的应力也随之发生变化。在此阶段，构件截面内部温度升高导致材料强度降低，截面外部处于降温区域的材料强度进一步降低，截面内外温差导致截面周围出现拉应力。上述因素的共同作用导致结构在火灾降温阶段发生破坏。相较于受火前，结构温度降至室温时结构的刚度降低、变形增加。     

性能化防火设计在特殊建筑结构抗火中的应用

目前,有许多大空间或特殊结构形式的建筑被建造,采用传统的法令性结构防火规范对这些建筑进行防火设计,会造成巨大浪费。基于建筑物的整体消防安全目标,确定结构的抗火设计要求,分析和总结了性能化结构防火设计思想及流程,并给出具体的实施方法。结合某超高层建筑实例,针对其顶部酒店大堂的独特"蛋"形结构及顶部拱形钢结构体系,利用大涡模拟技术和有限元模拟方法对整个结构的温度场及体系力学行为进行分区域计算,对体系钢构件的抗火承载力及稳定性验算,得出了合理的防火保护措施。实际工程项目的性能化结构防火设计,将对其他特殊结构的防火设计具有一定的参考价值。     

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.     

蔓延火灾下钢框架结构抗火性能试验研究

为研究蔓延火灾下钢框架结构建筑室内火灾温度场、钢构件温度分布和位移的发展规律,对1个足尺的两层钢框架结构进行蔓延火灾试验,测量试验区域内关键位置的空气温度、钢构件温度和位移。试验结果表明：试验中火源房间内的火灾过程呈现4个明显的发展阶段,受火70min时室内火灾达到全盛,测得火灾烟气层最高温度730℃;受火82min时火灾从火源房间蔓延至邻近房间,导致了邻近房间内各受火钢构件温度峰值出现在不同时刻,同时,各构件历经扩散热烟气加热、直接受火加热和冷却降温3个阶段,呈现反复升降温的受火过程;受火过程中,钢构件温度变化显著滞后于火场温度,受火钢柱先后升温产生向上的轴向变形。与传统室内火灾相比,蔓延火灾扩大了火场范围和钢结构受火范围,对结构安全和人员安全造成更大威胁,因此在进行结构抗火设计时应得到充分考虑。     

Research on fire resistance test of a steel frame building under spreading fire

为研究蔓延火灾下钢框架结构建筑室内火灾温度场、钢构件温度分布和位移的发展规律，对1个足尺的两层钢框架结构进行蔓延火灾试验，测量试验区域内关键位置的空气温度、钢构件温度和位移。试验结果表明：试验中火源房间内的火灾过程呈现4个明显的发展阶段，受火70min时室内火灾达到全盛，测得火灾烟气层最高温度730℃；受火82min时火灾从火源房间蔓延至邻近房间，导致了邻近房间内各受火钢构件温度峰值出现在不同时刻，同时，各构件历经扩散热烟气加热、直接受火加热和冷却降温3个阶段，呈现反复升降温的受火过程；受火过程中，钢构件温度变化显著滞后于火场温度，受火钢柱先后升温产生向上的轴向变形。与传统室内火灾相比，蔓延火灾扩大了火场范围和钢结构受火范围，对结构安全和人员安全造成更大威胁，因此在进行结构抗火设计时应得到充分考虑。     

Zur Frage der Nachnutzbarkeit verbundlos vorgespannter Stahlbetondecken nach Brandeinwirkung

The connection between fire exposure and the structural behavior of prestressed slabs after cooling This article shows the influence of fire exposure to the structural behaviour of slabs and prestressed slabs after cooling. The connections between the different fire exposures, the behaviour under fire and the structural behaviour after cooling are carried out. Concluding this, the text gives some information for constructing slabs with a good structural behaviour after fire exposure. The article “Verbundlos vorgespannte Decken – Nachnutzung nach Brand”, published in “Beton‐ und Stahlbetonbau” in August 2004, deals with the material properties of concrete, reinforcing steel and prestressing steel during and after fire exposure. In addition to this the results of some experiments on single‐span slabs and two‐span slabs are described. This new article has to be considered as a continuation and update.     

Study on the seismic performance of a multi‐tower connected structure

Many reinforced concrete or steel reinforced concrete single‐tower buildings have been built in China. The structural performance of such one‐tower structural systems depends on that of the primary components that are structural walls or moment‐resistant frames. For multi‐tower connected structures, problems become more complex. A multi‐tower connected building, with large floor slab openings in plan and long‐span truss in elevation, was thus studied because of its structural complexity and irregularity. First, a 1/25 scaled model structure was tested on the shake table under minor, moderate, and major earthquake levels. Then, the dynamic responses of the model structure were interpreted to those of the prototype structure according to the similitude laws. The experimental results were also compared with the numerical analysis of a three‐dimensional finite element model for the irregular structure. Both experimental and analytical results demonstrate that, despite of the structural complexity, the overall responses of the building meet the requirements of the Chinese design code and the torsion of the structure is not remarkable. It is suggested that the strength and stiffness of the long‐span connecting truss should be improved due to the potentially large vertical acceleration under strong earthquakes. Copyright © 2009 John Wiley & Sons, Ltd.     

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。     

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。     

Q690钢材高温后的力学性能试验研究

通过升温、冷却和拉伸试验,对历经300~900℃高温后的Q690钢材在自然冷却和浸水冷却条件下的力学性能展开试验研究。结果表明：经高温冷却的Q690钢材在不同温度和不同冷却方式下有不同的外观特征;受热温度超过500℃时,高温冷却对Q690钢材的弹性模量影响很小,对其强度和伸长率影响较大;当受热温度不超过700℃时,Q690钢材高温后的强度和伸长率在两种冷却方式下具有基本相同的变化规律;在700~800℃之间,不同冷却方式对Q690钢材高温后强度和伸长率产生影响,且随温度升高差别愈加明显,自然冷却条件下强度降低且伸长率增大,浸水冷却条件下强度增大且伸长率减小。将Q690钢材高温后力学性能与Q235钢材和Q460钢材比较,认为不同强度等级钢材高温后的力学性能差别显著,在自然冷却条件下较高强度钢材（Q690）的强度衰减和延性增长大于较低强度钢材（Q235和Q460）的。根据试验结果,建立了不同冷却条件下的高温后各力学参数与受热温度之间的数学模型,该模型可用于火灾后Q690钢结构的承载能力的评估。     

Performance-based analysis of large steel truss roof structure in fire

Due to the fast developments of large-space multi-functional architectures, large-span steel structures have been widely used in recent years. Therefore, the fire-resistance design of this kind of structures has attracted more attentions. Since traditional ISO834 standard fire curve is not suitable for large space structures, performance-based fire resistance design method is required. This paper presents the comprehensive case studies on the fire performance of a large space exhibition centre in Shanxi province, China under real fire scenarios including heating and cooling phases. The non-uniform fire temperature fields of the large space exhibition centre for the designed fire scenarios have been generated by using Fire Dynamic Simulator (FDS). A finite element (FE) model has been developed using FE software ANSYS for modelling the structural behaviour of the exhibition centre under different fire scenarios. Based on the results generated in this research some recommendations for the fire resistance design of large space steel truss structures have been proposed.     

Post-cooling properties of concrete exposed to fire

Concrete structures are able to resist high temperatures due to fire relatively well and they can be repaired afterwards. In order to select appropriate repair strategies, assessment of the condition of a concrete structure after fire is of crucial importance. Previous research has mostly been focusing on the strength of concrete during fire and considering slow cooling of elements to room temperature. Guidelines and models related to these conditions have been incorporated into structural design codes. However, in reality, fast cooling of concrete by means of water occurs frequently and the effect of this cooling method has been much less the subject of research investigations. Nevertheless, the effect of water cooling can be significant. In this article the effect of water cooling on the residual compressive strength, stress-strain diagram and bond strength between concrete and reinforcement is investigated. Two cooling methods are considered, i.e. quenching and spraying of specimens. It is found that the investigated properties are extremely sensitive to heating with subsequent water cooling.     

Numerische Simulation des Verhaltens von Betontragwerken unter Brandeinwirkung

Numerical Simulation of the Response of Fire Exposed Concrete Structure The proposed numerical model for concrete and reinforced concrete structures subjected to fire comprises the transient thermal and mechanical analysis considering the temperature dependent material properties of concrete and reinforcing steel within the framework of the phenomenological approach of the Eurocode 2, part 1‐2. A concrete model, based on the combination of plasticity and damage theory, serves as the basis for the material model of concrete for high temperatures. For reinforcing steel a standard elastic‐plastic material model is employed. The proposed model is validated by the numerical simulation of fire tests on plain concrete specimens and by the numerical simulation of a large scale fire test on a reinforced concrete slab. Furthermore it is used to determine the structural integrity of a tunnel structure, put up by the cut‐and‐cover method, exposed to fire.     

高强度螺栓过火冷却后力学性能试验研究

高强度螺栓连接是钢结构最常用的连接方式之一,其火灾后受力性能对整个结构灾后承载安全至关重要。通过对常用的8.8S和10.9S高强度螺栓进行高温过火冷却后力学性能试验研究,得到了过火温度对应力-应变关系曲线、屈服强度、抗拉强度和弹性模量的影响规律。试验包括自然冷却、泼水冷却两种冷却方式。研究结果表明：当过火温度超过400 ℃时,过火与冷却作用对高强度螺栓的力学性能将产生较大的影响;当过火温度超过700 ℃时,冷却方式对高强度螺栓的力学性能影响有较大的差别,在自然冷却条件下,延性不断加大,强度有略微回升,但幅度不明显;在泼水冷却的情况下,应力-应变曲线呈现明显脆性,塑性平台消失,强度大幅度回升,在过火温度超过800 ℃后10.9S高强度螺栓的强度甚至比未受火时提高约20%。