An experimental study of the mechanical behavior of steel planar tubular trusses in a fire

Experimental research has been conducted to study the mechanical behavior of two full-scale steel planar tubular trusses without fire-proof coating under fire conditions. The research aims to investigate the failure modes and temperature distribution of the steel planar tubular truss at elevated temperatures, as well as to validate the numerical related model. The experimental results demonstrate that the failure of the specimens was caused by local buckling of the brace members.     

Parametric analysis of mechanical behavior of steel planar tubular truss under fire

This paper presents experimental and numerical results of steel planar tubular truss, which was exposed to the fire condition. The principal aim is to investigate the critical temperature of the truss under permanent load and the influence of geometric parameter. It is found that both experimental and numerical results demonstrate that the failure of the steel planar tubular trusses is due to the local buckling of the brace members which validates the accuracy of finite element model. In the parametric analysis, it is found that the geometric parameters of the truss have a significant influence on the load bearing capacity of steel planar tubular truss subjected to the fire. The parameters include wall thickness ratio τ, diameter ratio β and chord diameter/thickness ratio γ. The results demonstrate that the critical temperature of the truss can be improved significantly by the increase of the brace diameter and the wall thickness of the chord while changing the wall thickness of the brace has limited effects. It is indicated from the analysis that at the higher load level, the parameters τ,β and γ have a distinct influence on critical temperature of the steel planar tubular truss.     

火灾下钢管T型节点抗冲击性能的试验研究

近海石油和天然气生产建筑容易发生爆炸和火灾。为了研究爆炸和火灾下结构的性能,对没有涂防火层的钢管T型节点进行试验。先对试件进行冲击,然后再在恒定荷载作用下进行加热。研究温度升高时T型节点的破坏模型、临界温度和温度分布;通过对比不受冲击荷载的试验,探索冲击荷载对节点力学性能的影响。结果表明:由于弦壁局部屈曲而导致的破坏模型与在室温下的破坏情况相同,但受冲击试件的临界温度为690℃,比不受冲击高。试验结果可对以后的数值研究进行验证。     

Experimental study of the mechanical behavior of steel staggered truss system under pool fire conditions

Experimental research has been conducted to study the mechanical behavior and failure mode of a 6-storey steel staggered truss system (SSTS) model made in 1/8 scale without fire-proof coating exposed to pool fire. The data of temperature distribution, displacements and strains of typical members were obtained. The results indicate that with the increase in temperature, local buckling appeared primarily on vertical web members of the Vierendeel panel of the truss directly exposed to fire, which contributed to the destruction of the original balance of the internal force. Afterwards, several joints of the truss exposed to fire, which connected diagonal web members with chords, were fractured. Catastrophic destruction of the truss exposed to fire was then observed. It can be inferred that the destruction of the truss exposed to fire may lead to the collapse of the two storeys supported by the truss, which would present a huge threat to the whole structure for the potential progressive collapse might be aroused.     

Fire-resistance study of restrained steel columns with partial damage to fire protection

In order to analyze the behavior of steel columns in fire with partial damage of fire protection, an analytical model is presented based on the differential equation of equilibrium, which may be used to predict the ultimate load bearing capacity of steel columns fixed at two ends and to predict the critical temperature of axially restrained steel columns. The imperfection of initial flexure of steel columns is taken into account in the model. The yielding of the edge fiber at the mid-span of a column subjected to elevated temperature is taken as the failure criteria for the fire resistance of the column. A numerical application is carried out to demonstrate the effect of the damage of fire protection on the ultimate load bearing capacity and axial force increase of axially restrained steel column in fire. Comparing with FEM, the model proposed in the paper has been validated and good agreement has been found.     

Behavior of steel columns in a fire with partial damage to fire protection

An experimental study is performed on two specimens in a furnace to investigate the fire behaviour of steel columns with partial loss of fire protection. The steel columns are connected by flush end-plates at two ends and the axial load is kept constant with a load ratio of 0.55 subjected to an elevation of temperature. The specimens are protected with 20 mm thickness of fire protection. The damaged length of fire protection is 7% of the complete length of the column for specimen S-1 and 14% for S-2 at the two ends of the steel columns. The temperature of atmosphere around the specimens in the furnace is assumed to follow the ISO834 standard temperature and the temperatures and displacements are measured in the experiment. The temperature distribution along the steel column is modelled by finite element analysis and compared with the measured results. A continuum model is presented to predict the ultimate load capacity or critical temperature of the columns with fire protection damage. Analyses are carried out on the specimens and compared with the experiment. Experimental and analytical results showed that the fire resistance of steel columns with partial damage to the fire protection is reduced. The damage length of the fire protection has a great effect on the fire resistance of steel columns. The failure of the specimens mainly resulted from the buckling or yielding at the portion where the fire protection is damaged.     

T形圆管相贯节点的抗弯性能足尺试验

介绍了进行T形相贯节点抗弯性能试验的方案设计.试验表明,试件在受弯作用下的破坏模式为节点处发生屈曲变形和支管处焊缝产生裂缝,说明T形相贯节点在一定条件下可以作为全刚性节点来进行设计,但在施工和加工过程中要保证焊缝的质量.     

轻骨料钢管混凝土短柱受火后力学性能的试验研究

钢管陶粒混凝土不仅具有陶粒混凝土轻质的特点,也拥有一般钢管混凝土结构的良好延性,但目前对火灾后钢管陶粒混凝土结构的性能还缺乏研究。通过对3组12根钢管陶粒混凝土短柱受火后力学性能的对比试验研究,讨论不同参数的钢管陶粒混凝土短柱受火后的剩余承载力和破坏形态的变化,重点讨论火灾最高保持温度、最高炉温持续时间、试件长细比、含钢率等参数对钢管陶粒混凝土短柱承载力和延性的影响。试验结果表明,钢管陶粒混凝土短柱受火后仍然具有较高的承载力和良好的延性,火灾后多数试件的荷载-位移曲线并没有出现下降段,甚至出现承载力部分下降后又重新上升的趋势。火灾持续时间及最高炉温对钢管陶粒混凝土短柱火灾后承载力的影响幅度与试件的几何参数有关,且试件的长细比越大,最高炉温变化对承载力所产生的影响越显著。     

高温下钢管自密实混凝土柱抗火性能试验研究

进行了圆钢管自密实混凝土柱的高温抗火性能试验研究,主要测量钢管表面的温度场、构件轴向变形和跨中侧向位移随时间的变化关系;分析了各种因素对耐火极限和轴向变形、跨中侧向位移曲线的影响规律。     

Experimental and numerical research on the critical temperature of laterally unrestrained steel I beams

Lateral unrestrained steel beams when subjected to high temperatures may collapse in service by lateral torsional buckling. This instability state may be predicted in the resistance, temperature and time domain. In this work the beam strength is determined in the temperature domain from a batch of numerical and experimental tests, with a specified degree of utilisation and a typical accident temperature rise.The experimental set-up is a reaction portal frame especially designed for beam elements under elevated temperatures. The specimens were heated by means of electroceramic resistances and a fibre mat specimen cover is used to increase the thermal efficiency. The material and the beam initial state conditions were considered, the experimental procedure being based on constant mechanical action under increasing thermal load.The experimental data was compared with numerical solutions, obtained from a geometric and material nonlinear analysis. A shell finite element modelling, with incremental and iterative procedures, was used in the numerical calculations. Good agreement was obtained between experimental and numerical data. However, both numerical and experimental results lead to higher critical temperatures when compared with the simplified calculation procedure presented in Eurocode for this case.     

钢管混凝土结构地震模拟试验研究

对钢管混凝土 5层框架结构进行了地震模拟试验 .通过振动台试验及理论分析 ,对钢管混凝土结构的动力特性、多种地震波输入下的结构加速反应和位移反应进行了对比 ,综合评定了钢管混凝土结构的抗震性能 ,为结构设计提供了参考数据     

Experimental behavior of steel beam-columns subjected to fire-induced thermal gradients

Fire tests were performed to investigate the mechanics and capacity of steel beam-columns that develop a thermal gradient through their depth when exposed to fire. Wide-flanged specimens were loaded axially and tested vertically in a furnace recently commissioned at Michigan State University. The placement of insulation simulated a realistic three-sided heating scenario such as that experienced by a column on the perimeter of a building frame. Specimens were tested with several combinations of load level, fire scenario, and direction of the thermal gradient (which dictates the direction of bending). The different combinations of tested parameters had a significant influence on the fire response of these columns, which all failed by full section yielding due to a combination of axial load (P) and moment (M). These columns developed bending moments in response to through-depth thermal gradients as well as a moment reversal due to a shift in the section’s center of stiffness. The plastic resistance to combinations of axial load and moment was also affected by the thermal gradients such that the critical section, located in the hottest region along the column length, was where moment was the smallest (not the largest, as would be intuitively expected). The experiments and computer models showed good agreement with the predicted demands (i.e. bending moment reversal) and capacity (i.e. changes in the plastic P-M capacity).     

Experimental study on local buckling of fire-resisting steel columns under fire load

The structural behavior of stub columns using fire-resistant steel has been investigated experimentally under uniform fire load. The newly-developed fire-resistant steel is proven to have higher strength at elevated temperature than that of conventional steel. Also, the requirement of fire-protection in the fire-resisting steel can be released or relaxed as compared with conventional steel structures. However, the design criteria for the application of the fire-resisting steel in steel columns are still limited. To examine the structural behavior of this type of steel columns under fire load, a total of 24 stub column specimens, including both box columns and H columns, reached their limit states due to axial load under fire condition. The main purpose of these studies is to evaluate the variations of the ultimate strength of steel columns due to different width-to-thickness ratios under specified elevated temperature; in addition, to investigate the reduction effects on column strength resulting in the increasing temperature; and finally, to establish the design guidelines of steel columns using fire-resisting steel. From the experimental results, it is found that the ultimate loads of the stub columns decrease while the width-to-thickness ratios or the temperature increases. However, with the increase of temperature, the effect of the width-to-thickness ratio on ultimate strength decreases. It is also found that the effect of the width-to-thickness ratio on the ultimate strength of box column at elevated temperature is more significant than that of H column. Based on these studies, design guidelines are proposed for the requirement of the width-to-thickness ratios of both box column and H column fabricated from fire-resisting steel.     

钢管混凝土柱火灾后力学性能理论分析

在介绍了钢材和混凝土两种材料受高温后的本构关系的基础上，进行数值模拟得出了高温后核心混凝土的σ-ε关系曲线，经过参数分析得出影响火灾后钢管混凝土压弯构件残余承载力的主要因素，最后得出了轴压弹性模量和轴压强度承载力的简化计算公式。     

Determination of the steel fire protection material thickness by an analytical process—a simple derivation

Structural fire safety is assured if the design value of the effect of the actions (thermal and mechanical) is lower than the design value of each structural element fire resistance or, in other words, structural safety is assured when the steel temperature in a fire situation only reaches values less than the structure critical temperature. The critical temperature is the temperature that causes structural collapse in a fire situation. The temperature in the structural element can be determined either experimentally or analytically. In the case of a structure covered with thermally protective material, such methods serve, in practice, to determine the thickness of the protective material. In this work, a previously unpublished expression for the calculation of the temperature in thermally protected steel structural elements in fire is derived. Comparisons with international recommendations and with experimental and numerical analysis results are made. In view of its simple form and derivation, the use of such expression is recommended for the revision of the Brazilian Standard “Steel structures fire design”.     

Performance of an unprotected steel structure subjected to repeated fire at a firefighter training facility

An evaluation of a single story unprotected steel structure exposed to repeated fire during the training of fire fighters is described. Temperatures are monitored on the structure using resistance temperature detectors connected to a data acquisition system. Temperatures of up to 384 °C are measured in the steel of the structures, which are below levels likely to cause much degradation in stiffness or strength. Uniform heating of the columns was shown to result in minimal stresses in the structure as the columns were relatively free to deform axially. Differential temperatures, however, where one side of the member is heated by a greater amount than the opposite side of the member, resulted in stresses calculated using an elastic analysis, up to 16 times greater than the yield strength and can thus explain large permanent curvatures observed in the columns. Coupon tests on steel samples from the columns exposed to repeated fire showed some hardening of the steel, possibility attributed to the plastic deformations in the columns, although the ultimate strain in the material was not greatly affected. Based on the monitoring and analysis, no aspects of the structure are considered to present an immediate hazard to the safety of the users. However, without improved cooling, plastic deformation of some members is expected.     

Calculating the buckling strength of steel plates exposed to fire

The local buckling capacity of fire-exposed steel cross sections is affected by the reduction in strength and stiffness associated with an increase in steel temperature. Using a stress-based approach, simple continuous equations that account for these reductions are proposed in this paper to calculate the ultimate strength of thin steel plates (i.e. idealized webs and flanges) at elevated temperature. Calculations made using the proposed equations show good agreement with computational results for a range of temperatures, boundary conditions, and loading scenarios. Comparisons with the results of previously published experiments show that the proposed approach provides a conservative prediction of experimentally measured buckling strengths of heated steel sections with thin plates. The proposed equations for calculating ultimate plate strength at elevated temperature offer a significant improvement over current AISC methods, which do not include an explicit temperature-based reduction of buckling capacity. The proposed equations are also a slight improvement over current Eurocode methods, which may become discontinuous for smaller values of plate slenderness. The proposed approach also has greater similarity to current North American standards than those of Eurocode.     

Experimental study on performance of elliptical section steel columns, under hydrocarbon fire

Elliptical structural steel hollow sections represent a recent addition to the range of steel sections available to structural engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance design guidance is restraining applications. This paper presents the first study ever conducted to investigate the fire resistance of steel columns with Elliptical Hollow Sections (EHS). Six columns of two slenderness λ=40.1 and λ=50.8 were tested under three loading levels (α_L=0.3,0.45 and 0.6) and subjected to a hydrocarbon fire curve. The paper provides the recorded data of axial displacements and temperature profiles of the EHS steel columns, while highlighting the unique local and overall buckling failure modes of the Elliptical Hollow Section.     

火灾下圆钢管混凝土柱温度场数值模拟

为研究圆钢管混凝土柱在火灾下的温度分布及火灾后的力学性能,利用有限元软件ABAQUS对火灾下圆钢管混凝土柱温度场进行计算和分析.分析结果表明,砂浆保护层的存在对内部钢管和混凝土有效地起到了阻火、隔热作用.采用有关试验数据与计算结果进行了对比,证明使用ABAQUS进行截面温度场的计算具有足够的精度,其方法是切实可行的.