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.     

Post-fire residual strength of steel tubular T-joint with concrete-filled chord

在试验研究基础上,对主管填充混凝土的T形节点受火后的剩余承载力进行有限元分析,结果表明：经历400℃以下的高温作用后,T形节点的剩余承载力未出现明显下降。但随着受火温度的升高,T形节点的剩余承载力呈非线性下降;同时,内填混凝土后钢管T形节点的受火后平均剩余承载力是相同参数空钢管T形节点剩余承载力的3倍以上,这是因为内填混凝土后可有效防止主管与支管节点处发生凹陷,使得钢管T形节点的破坏模式由节点相贯区主管凹陷破坏变为主管弯曲破坏,从而使钢管和混凝土的材料强度能够得到充分发挥;但内填混凝土抗压强度对承载力影响有限;此外,当试件从高温下冷却到常温后,由于混凝土强度未能同钢材得到较大恢复,因此内填混凝土T形节点受火后剩余承载力相比空钢管T形节点减少的更为明显。     

壁式钢管混凝土柱抗震性能试验研究

通过3个截面高宽比为3.0的壁式钢管混凝土柱足尺试件在高轴压比下的低周反复加载试验和有限元分析,研究壁式钢管混凝土柱的破坏模式、滞回行为、承载能力、变形性能和能量耗散能力。结果表明：试件的破坏模式为压弯破坏,破坏区域钢板受压鼓曲、钢管纵向焊缝涨裂、混凝土压溃;试件滞回曲线稳定饱满,无明显捏拢现象;纵向隔板能够约束钢管壁板平面外变形,提高钢板局部屈曲强度;试件破坏时位移延性系数大于3.0,等效黏滞阻尼系数大于0.4,减小钢管壁板宽厚比可有效增加试件耗能能力。设计轴压比为0.54～0.69时,壁式钢管混凝土柱屈服位移角大于0.005rad,极限位移角大于0.02rad,具有良好的变形性能和耗能能力。建立的精细有限元模型可准确预测壁式钢管混凝土柱在恒定轴力和反复水平力下的滞回行为。有限元分析表明,轴压比对壁式钢管混凝土柱的极限位移影响显著,提高含钢率可有效增加其承载力和变形性能。     

T形管节点落锤动态抗冲击性能试验研究

采用落锤冲击试验机进行了4个T形管节点的抗冲击性能试验研究。通过试验获得了冲击能量E、主管长径比（α=L/D）和主管直径D等参数对管节点破坏模态和变形模式的影响规律,分析了管节点在冲击力作用下整体和局部变形特性,以及冲击力、位移、应变时程曲线与冲击力 变形关系曲线。试验结果表明：主管长径比一定时,冲击能量的大小影响支管受撞T形管节点的破坏模态;破坏模态主要为主管上表面局部屈曲和主管上表面局部屈曲伴随主管整体弯曲变形两种形式;主管上表面局部屈曲产生的塑性变形区域受冲击力的影响不大,但其屈曲凹陷深度随着冲击能量的增大而增大;局部屈曲耗散了大部分冲击能量。基于能量的塑性铰线理论,提出了等效冲击承载力简化评估方法。     

高温作用后圆钢管钢筋混凝土轴压短柱力学性能试验研究

采用立式燃气试验炉对14根在核心混凝土中配置纵向受力钢筋的圆钢管钢筋混凝土短柱进行了按ISO 834标准升降温曲线的明火试验,其中2根短柱用于量测温度场,其余12根短柱冷却至室温后进行轴压静载试验。实测了受火阶段轴压短柱典型部位的截面温度分布和受火后的轴压荷载-轴向变形关系曲线,分析了升温时间和配筋率对受火后钢管钢筋混凝土短柱剩余承载力、刚度和延性的影响规律,同时进行了6根钢管钢筋混凝土短柱常温静载试验,与受火后对应轴压短柱比较,最后结合相关规范/规程提出了高温作用后圆钢管钢筋混凝土轴压短柱承载力的计算式。结果表明:钢管钢筋混凝土短柱受火后仍具有较高的承载力和良好的延性;升温时间对钢管钢筋混凝土短柱火灾后刚度和延性的影响明显大于对承载力的影响;配筋率的增大对钢管钢筋混凝土短柱的火灾后承载力、刚度和延性均有提高;所提计算式的计算结果与试验结果吻合较好,且偏于安全。     

装配式钢管混凝土柱-双钢梁框架节点受力性能试验研究

针对一种适合装配式结构的钢管混凝土柱-双钢梁框架体系,对其2个典型平面节点和2个典型空间节点进行单调和循环加载试验,以研究加载模式和节点类型对节点破坏形态、承载力、刚度、延性及耗能能力的影响。结果表明：试件的破坏均发生在梁端,柱与节点域保持完好,满足“强柱弱梁、强节点弱构件”的抗震设计要求;试件的位移延性系数为2.6~3.6,能量耗散系数为1.7~2.2,耗能能力与型钢混凝土节点相当;加载模式(单调或循环)相同而节点类型(平面或空间)不同时,节点性能差异小;加载模式不同而节点类型相同时,节点性能差异大：循环荷载作用下的节点梁端焊缝发生拉裂破坏,位移延性系数较小。该种节点静力性能较好,但从提高抗断裂能力出发,需进一步改进构造,对焊缝分布进行优化设计。     

L形钢管混凝土框架结构抗震性能试验研究

为了探讨L形钢管混凝土柱 钢梁框架的抗震性能,进行了4个1/2.5缩尺比例两层单跨L形钢管混凝土柱 钢梁空间框架的拟静力试验研究,主要考察了柱轴压比（n=0.4,0.6）、加载方向（β=0°,45°）对试件抗震性能的影响,对结构的破坏形态、破坏机制、滞回曲线、结构塑性铰出现的位置及次序、位移延性和耗能能力等性能进行了研究。试验结果表明：结构的破坏形态基本相同,梁端先屈曲,形成塑性铰,然后柱脚核心混凝土开裂压碎,钢管屈曲,形成塑性铰,节点核心区没有出现破坏现象,满足“强柱弱梁、强节点”的抗震设计要求;结构的滞回曲线呈饱满的梭形,强度和刚度退化不明显,变形能力和耗能能力较强;结构的延性较好,正向和反向的位移延性系数均大于4.0;轴压比对结构的抗震性能影响较大,随着轴压比的增大,框架的位移延性和耗能能力降低。     

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.     

Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints

A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer (CFRP) sheets was proposed and evaluated. The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses. Five T-joints were physically tested: one bare joint to obtain the peak load and corresponding displacement (D_1m), two reinforced joints to provide a reference, and two pre-damaged then retrofitted joints to serve as the primary research objects. The ratio of the pre-loaded specimen chord displacement to the value of D_1m was considered to be the degree of damage of the two retrofitted joints, and was set to 0.80 and 1.20. The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06% over the corresponding unreinforced specimens. However, the capacity of the retrofitted specimen was 2.51%–22.77% lesser compared with that of the directly reinforced specimens. Next, 111 numerical analysis models (0.63≤b≤0.76, 9.70≤g≤16.92) were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage. The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping, and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters. Finally, reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results. The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.     

钢管再生混凝土轴压长柱试验研究及力学性能分析

设计5个圆钢管再生混凝土长柱和5个方钢管再生混凝土长柱,对其进行轴压静力单调加载试验,考虑截面形式、再生粗骨料取代率、长细比3个变化参数,观察试件受力的全过程和破坏形态,得到试件屈服应变、峰值变形、承载力等重要特征点数据,绘制出荷载-变形、荷载-应变、轴压刚度-变形等关系曲线,并分析变化参数对试件承载力的影响规律,采用相关规程计算2种截面形式的钢管再生混凝土轴压长柱的承载力以及在正常使用极限状态下的刚度。试验研究和计算结果表明：钢管再生混凝土轴压长柱受力过程均经历了弹性阶段、屈服阶段和破坏阶段,破坏形态主要有材料强度破坏和弹塑性失稳破坏;再生粗骨料取代率对钢管再生混凝土轴压长柱的承载力影响不大;长细比对圆钢管再生混凝土试件承载力影响较大,随长细比的增加,试件的承载力逐渐降低,而对方钢管再生混凝土试件承载力影响较小。基于计算结果,给出了2种截面形式的钢管再生混凝土轴压长柱的承载力及轴压刚度的设计建议。研究结果可为钢管再生混凝土结构的进一步研究和推广应用提供参考。     

Experimental analysis on cold-formed steel beams subjected to fire

The great majority of the studies in this area emphasise further the structural behaviour of cold-formed steel members by means of analytical approximation and purely numerical methods. In addition, they generally only take into account the structural behaviour of members with just one profile. On the contrary, this paper reports a series of flexural tests under fire conditions focused on cold-formed galvanised steel beams consisting on compound cold-formed steel profiles which are often used in floors and roofs of warehouses and industrial buildings. The main objective of this research was to assess the failure modes, the critical temperature and the critical time of the studied beams. Other important goals of this research work were also to investigate the influence of the cross-sections, the axial restraint to the thermal elongation of the beam and the rotational stiffness of the beam supports. Finally, the results showed above all that the critical temperature of a cold-formed steel beam might be strongly affected by the axial restraint to the thermal elongation of the beam.     

约束钢柱抗火性能试验研究

介绍了一组约束钢柱抗火试验,包括试验设计、钢柱温度和位移测量结果、钢柱试验后残余变形,以及试验的数值模拟等。试验变化参数为钢柱所受约束的刚度。约束刚度大小对钢柱抗火性能的影响包括:约束刚度比大的钢柱,其屈曲温度和破坏温度均较低;钢柱屈曲后,约束刚度比大的钢柱在变形较小时即可达到新的平衡位置;约束钢柱的破坏温度一般高于其屈曲温度,且随轴向约束刚度比的增大,破坏温度与屈曲温度之差增大。试验结果与有限元分析结果进行了对比,两者吻合较好,有限元方法研究约束钢柱抗火性能具有较高的精度。     

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。     

斜向受力十字形钢管混凝土柱抗震性能试验研究

为研究十字形钢管混凝土柱在斜向受力下的抗震性能,以加载角度(0°和45°)、混凝土强度等级(C50和C70)、轴压比(0、0.25和0.5)以及是否设置加劲肋为试验参数,进行了9根十字形钢管混凝土柱在往复荷载作用下的试验研究,获得了柱的破坏形态、水平荷载-位移滞回曲线、骨架曲线、延性、累积耗能、变形等特性,分析了不同参数对柱抗震性能的影响规律。并建立了十字形钢管混凝土柱的有限元模型,有限元分析结果与试验结果吻合良好。试验结果表明:十字形钢管混凝土柱具有较好的滞回性能,所有柱的位移延性系数均高于3.5;轴压比对十字形钢管混凝土柱的抗震性能影响较大,轴压比越大,柱承载力越低,刚度退化越快,延性和耗能能力也越差;随着混凝土强度的增加,柱承载力增加,轴压比较大时,混凝土强度越高,延性下降越明显;内部间断焊接加劲肋的柱比未设置加劲肋柱的承载力提高约8%,但延性和耗能能力提高不大;加载角度为45°柱的滞回性能稍优于0°的柱。     

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。