轴向约束型钢混凝土柱耐火性能试验研究

为了考察受轴向约束的型钢混凝土柱的耐火性能,以荷载比、偏心率和含钢率为参数,开展了7根轴向约束型钢混凝土柱的耐火试验。采用恒载升温模式,研究了火灾下受轴向约束的型钢混凝土柱的温度分布、位移、变形、耐火极限及破坏形态。试验结果表明：荷载比相同时,施加在轴心受压柱顶的竖向荷载大于偏心受压柱。对于轴心受压柱,高温下柱首先缓慢膨胀,然后逐渐压缩破坏;由于轴向约束分担了柱的竖向荷载,压缩变形随时间变化较为缓和,轴向约束延长了柱的耐火极限。对于偏心受压柱,高温下其膨胀变形大于轴心受压柱,且膨胀变形先增加再减小;轴向约束增加了柱的竖向荷载,缩短了柱的耐火极限。荷载比对轴向约束型钢混凝土柱耐火极限影响显著,荷载比越大,耐火极限越小。当荷载比不大于0.5时,偏心率越大,柱的耐火极限会相应增大。含钢率增加,会在一定程度上延长柱的耐火极限。     

Fire performance of axially restrained steel reinforcedconcrete columns

为了考察受轴向约束的型钢混凝土柱的耐火性能，以荷载比、偏心率和含钢率为参数，开展了7根轴向约束型钢混凝土柱的耐火试验。采用恒载升温模式，研究了火灾下受轴向约束的型钢混凝土柱的温度分布、位移、变形、耐火极限及破坏形态。试验结果表明：荷载比相同时，施加在轴心受压柱顶的竖向荷载大于偏心受压柱。对于轴心受压柱，高温下柱首先缓慢膨胀，然后逐渐压缩破坏；由于轴向约束分担了柱的竖向荷载，压缩变形随时间变化较为缓和，轴向约束延长了柱的耐火极限。对于偏心受压柱，高温下其膨胀变形大于轴心受压柱，且膨胀变形先增加再减小；轴向约束增加了柱的竖向荷载，缩短了柱的耐火极限。荷载比对轴向约束型钢混凝土柱耐火极限影响显著，荷载比越大，耐火极限越小。当荷载比不大于0.5时，偏心率越大，柱的耐火极限会相应增大。含钢率增加，会在一定程度上延长柱的耐火极限。     

偏心受压钢管混凝土叠合柱耐火性能研究

基于试验验证的三维有限元模型,对火灾下方形截面钢管混凝土叠合柱偏心受压极限承载力和耐火极限的变化规律开展了参数分析。研究结果表明:与常温状态相比,在180 min升温时间内,钢管混凝土叠合柱偏心受压极限承载力的降幅可超过60%。荷载偏心率不同时,火灾下叠合柱的偏心受压极限承载力的降幅比较接近。受火面数量、截面核心面积比、截面边长和长细比均对火灾下叠合柱的偏心受压极限承载力的降幅有影响。大偏心受压钢管混凝土叠合柱的耐火极限高于小偏心受压钢管混凝土叠合柱的耐火极限。     

三面受火的方中空夹层钢管混凝土柱耐火极限分析

为研究三面受火方中空夹层钢管混凝土柱的抗火性能,通过ABAQUS有限元软件建立了三面受火的方中空夹层钢管混凝土柱有限元模型,并将计算结果与试验数据进行对比,结果吻合良好。利用所建立的模型分析了构件在三面受火条件下的温度场与受力机理,并分析了常见参数对三面受火方中空夹层钢管混凝土柱耐火极限的影响,提出了三面受火方中空夹层钢管混凝土柱耐火极限的简化计算公式。结果表明,在荷载比为0.4～0.8、长细比为20～50、截面尺寸为400～1 000 mm常用参数范围内,荷载比、长细比、截面尺寸和荷载偏心率是构件耐火极限的主要影响参数,荷载比和长细比越小,截面尺寸越大,构件耐火极限越大。当0≤e/r_0≤0.4时,荷载偏心率对构件的耐火极限影响较大,耐火极限最大可比轴压时高50%。     

典型受火方式下型钢混凝土异形柱耐火极限研究

应用有限元软件ABAQUS建立型钢混凝土柱数值模型,研究4种典型受火方式下SRC异形柱的耐火性能,探讨各因素对SRC异形柱耐火极限的影响。结果表明:矩形柱耐火性能优于异形柱;对于任意截面的SRC柱,耐火极限均随荷载比的增大而减小,且矩形和L形SRC柱在高荷载比时下降更多;荷载比较小时L形柱的耐火性能优于T形柱,荷载比较大时T形柱的耐火性能优于L形柱;实腹式配钢SRC柱的耐火性能优于空腹式。研究结果可为SRC异形柱的抗火设计提供依据和参考。     

型钢混凝土约束柱耐火极限实用计算方法

利用ABAQUS有限元软件,建立了热力耦合作用下四面受火型钢混凝土约束柱的数值分析模型,该模型得到了已有试验数据的验证。应用上述模型,详细考察了轴向约束刚度比、转动约束刚度比、荷载比、偏心率、截面尺寸、含钢率、截面配筋率等参数对型钢混凝土约束柱耐火极限的影响规律。对影响型钢混凝土约束柱耐火极限的各种参数进行详细计算分析,结果表明轴向约束刚度比、荷载比、偏心率、截面尺寸和混凝土强度是影响耐火极限的主要因素。通过大量计算给出了型钢混凝土约束柱耐火极限的实用抗火计算方法。     

SRC和RC柱耐火性能和抗火设计的若干问题探讨

扼要介绍了影响型钢混凝土SRC和RC钢筋混凝土柱耐火极限的可能因素主要有截面尺寸、构件长细比、火灾荷载比、截面配筋率、截面含钢率、荷载偏心率、截面高宽比、钢材和混凝土强度等的几何参数、物理参数和荷载参数等对SRC和RC构件.构件耐火极限的影响规律,探讨了SRC和RC柱耐火性能和抗火设计中的若干问题。     

单面受火的方钢管约束钢筋再生混凝土柱耐火极限

为研究单面受火的方钢管约束钢筋再生混凝土柱的耐火极限,采用有限元软件ABAQUS建立了ISO-834标准火灾作用下单面受火的方钢管约束钢筋再生混凝土柱有限元模型,相关试验验证之后、分析了截面温度场和应力场的变化规律。在此基础上分析取代率、混凝土强度、荷载比、含钢率、荷载偏心率、荷载角、配筋率、截面尺寸和钢材强度等参数对构件耐火极限的影响规律。结果表明：荷载偏心率和荷载角对构件耐火极限影响较为复杂,当荷载角为180°时,荷载偏心率由0.2增加到0.4,构件耐火极限增加11.2%;当荷载偏心率为0.8时,荷载角由0°增到90°,构件耐火极限降低32.2%;荷载比和截面尺寸对构件耐火极限影响明显,当含钢率为5.33%时,荷载比由0.4增到0.5,其耐火极限降低37.1％;当钢材强度为Q345时,截面尺寸由200mm增到300mm时,构件耐火极限增加66.73%。基于上述规律并结合计算结果给出了单面受火的方钢管约束钢筋再生混凝土柱的耐火极限简化计算式,可为该类柱抗火设计提供参考。     

相对两面受火的方钢管约束型钢混凝土柱抗火性能

为研究相对两面受火的方钢管约束型钢混凝土柱的耐火极限,运用ABAQUS建立了ISO 834标准火灾作用下方钢管约束型钢混凝土柱的有限元模型,包括温度场分析模型和耐火极限分析模型,用已有的相关试验进行验证,并分析了截面温度场和力学性能的变化规律。在此基础上分析荷载比、计算长度、型钢含钢率、截面尺寸、混凝土强度等参数对构件耐火极限的影响规律。基于上述规律并结合大量计算结果定量给出了相对两面受火的方钢管约束型钢混凝土柱的耐火极限简化计算式。结果表明:荷载比和计算长度对构件耐火极限影响较大,随着荷载比和计算长度的增加,构件的耐火极限呈线性降低; 截面尺寸对构件的耐火极限影响较大,随着截面尺寸的增加,构件的耐火极限呈线性增加; 随着型钢含钢率的增加,构件的耐火极限增加并不明显; 耐火极限计算式计算精度良好,可为相对两面受火的方钢管约束型钢混凝土柱抗火设计提供参考。     

三面受火高强混凝土柱耐火极限研究

编制了三面受火高强混凝土柱高温全过程分析程序,程序的有效性得到试验数据的验证.利用该计算程序,分析了截面尺寸、轴压比、配筋率、计算长度和荷载偏心率等参数对ISO 834标准升温过程作用下三面受火高强混凝土柱耐火极限的影响规律.针对三面受火高强混凝土柱的不同截面尺寸、轴压比、配筋率、计算长度和荷载偏心率共4800种工况进行了高温反应分析.在此基础上,定量给出了该类构件耐火极限的实用计算方法.结果表明:严格控制轴压比和偏心率是提高三面受火高强混凝土柱耐火极限的有效措施.     

Fire resistance of concrete encased steel columns under 3- and 4-side standard heating

Results from seven fire resistance experiments on concrete encased steel (CES) columns under standard fire exposure conditions are presented. The test parameters include column size, 3- and 4-side fire exposure, load intensity and load eccentricity. Data from the tests is utilized to study the effect of the aforementioned parameters on thermal and structural response of concrete encased steel columns. Test results show that CES columns have higher fire resistance under 3-side heating than that under 4-side heating. Also, load ratio and load eccentricity have a noticeable influence on the fire resistance of CES columns. In addition, spalling of the concrete decreases the fire resistance of CES columns. A comparison of measured fire resistance of CES columns with those predicted using current code provisions indicate that the current provisions may not be conservative in some situations.     

三面及四面受火钢骨混凝土柱的耐火性能

在标准火灾条件下进行钢骨混凝土柱的耐火试验。以几何尺寸、三面或四面受火、荷载大小及偏心为参数,研究其对钢骨混凝土耐火性能的影响。结果表明:钢骨混凝土柱三面受火条件下的耐火性能高于四面受火;载荷比和荷载偏心的影响可以忽略;混凝土的剥落降低了柱耐火性能。将试验结果与现有规范进行对比可知,某些条件下,按规范计算的耐火性能可能偏高。     

非均匀受火下约束型钢混凝土柱力学性能研究

为了解不同受火条件下型钢混凝土柱截面温度场,同时考察受火方式、火灾荷载比、荷载偏心率、约束刚度比等参数对型钢混凝土柱抗火性能的影响,进行了14个包括四面、三面、相对两面、相邻两面、单面受火条件下轴向约束型钢混凝土柱的抗火性能试验。试验结果表明：受火面数量、受火方位对 型钢混凝土柱截面温度分布有显著影响,升温时间相同时,四面受火、三面受火、两面受火、单面受火试件截面相同位置处所经历的最高温度依此降低;距试件表面距离相同时,型钢翼缘外侧受火面温度比型钢腹板外侧受火面温度略高。受火方式、火灾荷载比、荷载偏心率、约束刚度比对升降温全过程下型钢混凝土柱轴向变形和轴力发展有显著影响,试件受热膨胀变形和降温压缩变形随受火面数的增多而增大;轴向膨胀变形随火灾荷载比的增大而减小,随荷载偏心率的增大而增大;荷载比越大,试件由轴向拉伸状态转为轴向压缩状态的时间越短,压缩程度越高。定义试验实测轴力与初始施加轴力的比值为轴力变化系数,四面受火、三面受火、两面受火、单面受火时,试件升降温后期的轴力变化系数依此递减,轴力变化系数峰值随荷载偏心率和轴向约束刚度比的增大而增大,随火灾荷载比的增大而减小。     

Experimental research on the behaviour of eccentrically loaded SRC columns subjected to the ISO-834 standard fire including a cooling phase

This paper presents an experiment study of the post-fire behavior of five SRC columns under combination of axial eccentrical loading and fire. The experiment phenomena and mechanical response of the SRC column specimens during experiment, specifically loading, heating, cooling and post-fire loading were observed. The residual load bearing capacity, failure modes and vertical deformation were studied. With the test program, the effects of parameters such as the load ratio, the fire duration time and the steel ratio were studied. It is shown that the effects of temperature delay become more obvious with the increase of the depth from the heated surface. Some of the SRC column specimens failed during the cooling phase. For other specimens residual deformations were observed when the furnace temperature decreased to ambient temperature. The influence of some parameters including the load ratio, the fire duration time and the steel ratio on the post-fire load bearing capacities was discussed. It can be concluded that the residual load bearing capacity of the SRC columns decreases with the increase of the fire duration time and the load ratio, and increases with the increase of the steel ratio. Finally, a finite-element analysis model was developed to simulate the behavior of the tested SRC columns.     

钢筋混凝土T形柱的耐火极限研究

利用数值模拟程序分析了荷载比、计算长度、截面尺寸、荷载偏心率、配筋率和荷载角等参数对ISO834标准升温过程下钢筋混凝土等肢T形柱耐火极限的影响规律。针对不同荷载比、计算长度、截面尺寸、荷载偏心率、配筋率和荷载角共5400种工况进行了四周受火时等肢T形柱的高温反应分析。在此基础上,定量给出了该类构件耐火极限的实用计算方法。研究表明:(a)严格控制荷载比是提高T形柱耐火极限的有效措施。(b)随着计算长度的增加,T形柱耐火极限近似呈直线降低。(c)当荷载偏心率在0和1.0之间变化时,T形柱耐火极限随荷载偏心率的增大而减小。当荷载偏心率在1.0和2.0之间变化时,荷载偏心率改变对T形柱耐火极限影响较小。(d)荷载角对T形柱耐火极限影响较大且影响规律较为复杂。     

Numerical analysis on structural behaviors of concrete filled steel tube reinforced concrete (CFSTRC) columns subjected to 3-side fire

The structural behaviors of concrete filled steel tube reinforced concrete (CFSTRC) columns, which were exposed to a 3-side fire were discussed by using the non-linear finite element analysis (FEA) software ABAQUS. Details of the temperature distribution, fire resistance, failure modes, redistribution of internal force, contact stress between the steel tube and the concrete (both inside and outside of the steel tube), and the development of stress and strain within the CFSTRC columns subjected to a 3-side fire were revealed. The factors that may have affected the fire resistance of the CFSTRC columns exposed to three-side fire were analyzed. Based on the above research, the present study observed uniaxial symmetry on the cross-sectional thermal distribution of the CFSTRC, wherein a significantly lower temperature on the unexposed side was observed as compared to the exposed side. The two side verges of the surface, which were not exposed to fire, exhibited the lowest temperature. Following the end of the heating, the maximum temperature difference reached about 1065oC. The large temperature difference would bring non-uniform thermal stress and strain, and accidental eccentricity. In addition, the existence of concrete inside and outside of the steel tube prevented the steel tube from occurring local buckling, and the failure modes of CFSTRC columns acted as overall bucking. Parameters such as the fire load ratio, sectional dimension, slenderness ratio, sectional core area ratio, and external concrete compression strength significantly influenced the fire resistance of the CFSTRC columns. Finally, a simplified calculating formula was proposed to calculate the fire resistance influence factors of the CFSTRC columns subjected to three-sid fire. The formula-calculated results were well in agreement with the finite element analysis results, thereby providing a simple and feasible method for evaluating the fire-resistance design of these types of components in practical engineering.     

Fire resistance of concrete filled square steel tube columns subjected to eccentric axial load

The fire resistance of concrete filled square steel tube columns (CFT columns) without fire protection under a constant axial load has been previously examined. The purpose of this present study is to investigate the fire resistance of CFT columns when they are subjected to combined loads. This paper presents a nonlinear thermal stress analysis method for predicting the mechanical behavior and fire resistance of CFT columns under eccentric axial load (axial load and flexure moment). This method is based on the stress-strain characteristics of materials at high temperatures and on the mechanics of column deflection curves. From the results of the developed computational technique, it was demonstrated that as the yield stress and rigidity of the steel tube rapidly decreased for approximately 30 minutes, the decrease of flexure moment capacity increased significantly more than that of the axial load capacity. In addition, as the load eccentricity ratio increased, the fire resistance time drastically decreased. However, the time of maximum expansion under eccentric axial load was independent of the load eccentricity ratio.     

Behavior of axially-and-rotationally restrained concrete columns with ‘+’-shaped cross section and subjected to fire

Most of the previous investigations studied the structural behavior of concrete columns with ‘+’-shaped cross section at room temperature, but the behavior of such columns during a fire and the effect of boundary conditions on the mechanical properties of the heated columns have seldom been examined. In this paper, the influence of axial-and-rotational restraint on the behavior of heated concrete columns with ‘+’-shaped cross section is investigated. A self-developed finite element program RCSSCF is applied in this study. The development of column internal forces as well as deflections at the mid-height of concrete columns are discussed. Simulation results show that: (1) axial restraint can induce significant additional axial forces in concrete columns with ‘+’-shaped cross section and subjected to fire, and the additional axial forces in strongly restrained concrete columns during a fire can reach approximately 65–70% of the axial forces in columns at room temperature; (2) the fire resistance of concrete columns without rotational restraint decreases significantly with an increase of load eccentricity ratio, but that with rotational restraint is influenced lightly by load eccentricity ratio; and (3) for columns with different non-zero rotational restraint ratios, the internal axial forces, and the internal moments and deflections at the mid-height of these columns appear to follow common trends.     

高强度Q690钢柱耐火性能试验研究

为了获得高强度Q690钢柱的耐火性能，使用电炉对无防护足尺焊接H形Q690钢柱进行模拟ISO 834升温条件下耐火试验。测量得到不同荷载比下Q690钢柱温度、轴向位移、侧向位移与受火时间的关系，基于试验数据得到钢柱的临界温度和耐火极限。采用ABAQUS有限元软件建立钢柱耐火性能分析模型，考虑钢材高温蠕变和焊接残余应力的影响，模拟得到了钢柱的受火响应，其与试验结果吻合良好。利用验证的有限元模型分析了荷载比、长细比和升温速率对钢柱受力性能的影响。研究表明，无防护的Q690钢柱在受火20min左右发生破坏，破坏模式为整体失稳破坏；荷载比对临界温度影响较大，长细比和升温速率影响较小；Q690钢柱的临界温度比GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EN 1993-1-2的计算结果低60℃左右。最后提出了高强Q690钢柱抗火设计的简化方法。