Fire behavior of axially loaded slender high strength concrete-filled tubular columns

This paper describes sixteen fire tests conducted on slender circular hollow section columns filled with normal and high strength concrete, subjected to concentric axial loads. The test parameters were the nominal strength of concrete (30 and 80 MPa), the infilling type (plain concrete, reinforced concrete and steel fiber reinforced concrete) and the axial load level (20% and 40%). The columns were tested under fixed-pinned boundary conditions and the relative slenderness at room temperature was higher than 0.5 in all of the cases. A numerical model was validated against the tests, in order to extend the results and understand the failure mode of such columns. It is the aim of this paper to study the influence in a fire situation of the use of high strength concrete, as opposed to normal strength concrete. The results have shown that for slender columns subjected to high temperatures, the behavior of high strength concrete was different than for stub columns, spalling not being observed in the experiments. Furthermore, the addition of steel fibers was not found very advantageous in slender columns, since no increment in terms of fire resistance was obtained for the columns which used this type of reinforcement. However, the addition of reinforcing bars seems to be the solution in some cases, where the use of external fire protection wants to be avoided in the design of HSS structures, since the reinforcing bars allow the tube to resist a higher axial load.     

空间钢构架混凝土柱的试验研究与设计建议

通过 2根空间钢构架混凝土轴心受压短柱及 1根普通钢筋混凝土轴心受压短柱的对比试验研究 ,以及 4根空间钢构架混凝土偏压短柱的试验研究 ,分析了空间钢构架混凝土柱的破坏特征 ,提出了其设计计算方法和构造要求。     

偏心荷载作用下细长型高强钢管混凝土柱的防火性能

对受偏心轴向荷载作用、分别填充普通混凝土和高强混凝土的细长型圆钢管柱进行24组防火试验。此试验是对Romero等人在2011年所做的中心荷载柱的试验结果的进一步探讨。此防火试验中的试验参数涵盖了混凝土标准强度(30MPa和90MPa)、填充类型(普通混凝土、钢筋混凝土和钢纤钢筋混凝土)、轴向荷载水平(20%和40%)和荷载偏心(20mm和50mm)。在固定的边界条件下对室内温度下相对长细比高于其他样本0.5的柱进行试验。研究这种内填混凝土组合件偏心荷载的影响。试验结果显示,与填充普通混凝土的柱相比,添加钢纤维并不能提高细长型柱在偏心荷载下的防火性能。然而,在混凝土柱中添加钢筋则可以提高防火性能。在中空圆钢管中填充混凝土可以提高其防火性能,钢管高强混凝土柱在承载力方面有更明显的提升。与欧洲规范4-1-2中的简易计算模型相比较,尽管此方法可用于偏心荷载作用下的柱,但在预测内填普通混凝土柱和钢纤维钢筋混凝土柱时仍会产生较大的误差。     

钢筋混凝土分体柱框架抗震性能的模型试验研究

本文通过一榀1/3比例的两跨三层现浇钢筋混凝土分体柱框架模型的低周反复荷载试验,研究了分体柱框架模型的破坏机制、出铰顺序、滞回特性、耗能能力等抗震性能;研究了分体柱框架的裂缝发展、分体柱与其他构件的变形协调、内力重分配等工作过程;探讨了分体柱的过渡区、配箍率等主要参数对分体柱框架抗震性能的影响。验证了已有的分体柱及分体柱框架梁柱节点的设计方法和构造要求;研究了分体柱框架强柱弱梁、强剪弱弯以及强节点、强锚固的关系;给出了分体柱轴压比、剪跨比等概念参数的定义。从而得出结论,采用分体柱可以实现变短柱为长柱的设计思想,有效地改善钢筋混凝土短柱、特别是超短柱框架的延性和破坏形态,大幅度地提高钢筋混凝土短柱、特别是超短柱框架的抗震能力,最后给出了相关的设计建议。     

Behaviour of reinforced and concrete-encased composite columns subjected to biaxial bending and axial load

An experimental investigation of the behaviour of reinforced concrete columns and a theoretical procedure for analysis of both short and slender reinforced and composite columns of arbitrarily shaped cross section subjected to biaxial bending and axial load are presented. In the proposed procedure, nonlinear stress–strain relations are assumed for concrete, reinforcing steel and structural steel materials. The compression zone of the concrete section and the entire section of the structural steel are divided into adequate number of segments in order to use various stress–strain models for the analysis. The slenderness effect of the member is taken into account by using the Moment Magnification Method. The proposed procedure was compared with test results of 12 square and three L-shaped reinforced concrete columns subjected to short-term axial load and biaxial bending, and also some experimental results available in the literature for composite columns compared with the theoretical results obtained by the proposed procedure and a good degree of accuracy was obtained.     

Fire behavior of axially loaded slender high strength concrete-filled tubular columns

This paper describes sixteen fire tests conducted on slender circular hollow section columns filled with normal and high strength concrete, subjected to concentric axial loads. The test parameters were the nominal strength of concrete (30 and 80 MPa), the infilling type (plain concrete, reinforced concrete and steel fiber reinforced concrete) and the axial load level (20% and 40%). The columns were tested under fixed-pinned boundary conditions and the relative slenderness at room temperature was higher than 0.5 in all of the cases. A numerical model was validated against the tests, in order to extend the results and understand the failure mode of such columns. It is the aim of this paper to study the influence in a fire situation of the use of high strength concrete, as opposed to normal strength concrete. The results have shown that for slender columns subjected to high temperatures, the behavior of high strength concrete was different than for stub columns, spalling not being observed in the experiments. Furthermore, the addition of steel fibers was not found very advantageous in slender columns, since no increment in terms of fire resistance was obtained for the columns which used this type of reinforcement. However, the addition of reinforcing bars seems to be the solution in some cases, where the use of external fire protection wants to be avoided in the design of HSS structures, since the reinforcing bars allow the tube to resist a higher axial load.     

预应力CFRP布加固负载混凝土柱轴心受压性能研究

为开展轴心压力作用下预应力碳纤维增强复合材料（CFRP）布加固负载圆形截面混凝土短柱力学性能研究,设计制作了11根圆形截面混凝土短柱,其中1根普通混凝土柱为对比柱,其余10根混凝土柱在负载与非负载2种情况下分别利用预应力CFRP布或非预应力CFRP布进行加固。通过轴心加载试验,获得了各试件极限荷载、轴向变形、材料应力变化等试验数据。基于试验数据分析了试件轴心压力作用下的力学性能。结果表明:与普通混凝土柱相比,利用预应力CFRP布加固的负载混凝土柱在二次受力过程中其屈服荷载有显著提高,且提高幅度与CFRP布预应力水平成正比,但极限承载力与CFRP布的预应力水平无关;利用预应力CFRP布加固的负载混凝土柱延性性能有显著提高。     

高强螺旋箍筋约束混凝土柱连接抗震性能试验研究与理论分析

对于采用高强螺旋箍筋约束混凝土柱的装配整体式框架结构,提出了一种新的柱-柱连接方式,即在局部外包钢管设置横穿栓筋进行连接。制作足尺装配整体式柱和整浇柱试件,对其进行低周反复加载拟静力试验。通过观测试件的受力、变形、破坏过程及破坏形态,分析其承载能力、变形能力和耗能能力,验证了新型连接的可靠性。结果表明：在高轴压比下,采用新型连接的高强螺旋箍筋约束混凝土装配整体式柱与相应整浇柱均具有良好抗震性能,可以替代整浇柱应用于高烈度地震设防区的建筑结构中。结合试验,对新型连接的受力机制进行理论分析,提出了连接屈服荷载和破坏荷载的计算式,并通过计算结果与试验结果的比较,验证了理论公式的正确性。     

Modelling of probability of failure of concrete columns

This paper predicts the probability of failure or short and long columns of square reinforced concrete for deterministic and probabilistic loads. The effect of various parameters; width, length of column, effective length coefficient, percentage of steel, axial load, grade of concrete and random numbers; on the probability of failure of the column is studied. The material, geometric parameters and the load are treated as probabilistic. The results for short columns show that the rate of decrease of probability of failure is a maximum with increase in width, while it increased to a maximum with increase in loads, whereas for long columns the length of column had the predominant effect.     

基于简化修正压力场理论的钢筋混凝土柱荷载-变形分析

基于简化修正压力场理论对钢筋混凝土柱抗剪机理进行了分析,并考虑核心混凝土膨胀对箍筋抗剪承载力贡献的影响,计算了骨料咬合作用及受压区的抗剪承载力贡献,获得受拉区和受压区的抗剪强度,从而建立箍筋屈服后柱构件抗剪强度计算方法;结合传统截面纤维分析法,同时引入弯曲变形、剪切变形及滑移变形3种变形分量,在箍筋屈服前对柱构件进行抗弯分析,最终得出压弯剪作用下钢筋混凝土柱荷载-变形曲线,并与所收集的15个钢筋混凝土柱低周反复试验结果进行了对比。研究结果表明:采用该方法计算的荷载-变形曲线与试验骨架曲线吻合较好,对发生弯曲破坏、弯剪破坏及剪切破坏3种不同破坏类型的钢筋混凝土柱均有较好的分析效果,可用于压弯剪作用下钢筋混凝土柱的荷载-变形分析。     

Fire behavior of eccentrically loaded slender high strength concrete-filled tubular columns

This paper describes a series of 24 fire tests conducted on slender circular hollow section columns filled with normal and high strength concrete, subjected to eccentric axial load. It is a continuation of a previous research paper (Romero et al., 2011 [1]), where test results on centrally loaded columns were presented. The test parameters covered in this fire testing program were the nominal strength of concrete (30 and 90 MPa), the infilling type (plain, bar-reinforced and steel fiber reinforced concrete), the axial load level (20% and 40%) and the load eccentricity (20 and 50 mm). The columns were tested under fixed-pinned boundary conditions, with a relative slenderness at room temperature higher than 0.5 for all the specimens. The aim of this paper is to study the influence of eccentricity in combination with the type of concrete infill. The results show that the addition of steel fibers does not improve the fire resistance of slender columns under eccentric loads, as compared to columns filled with plain concrete. However, the addition of reinforcing bars increases the fire resistance of the columns in this situation. Filling the steel hollow section columns with concrete increases their fire resistance, the increase in load bearing capacity being more noticeable for columns filled with high strength concrete. A comparison with the current simple calculation model in Eurocode 4 Part 1.2 shows that, although the method is safe for eccentrically loaded columns, it produces a high error in the predictions for columns filled with plain or steel fiber reinforced concrete.     

Influence of ultra-high strength infill in slender concrete-filled steel tubular columns

This paper describes 24 tests conducted on slender circular tubular columns filled with normal, high, and ultra-high strength concrete for plain, bar reinforced and steel fiber reinforced columns. These were reinforced and subjected to both concentric and eccentric axial load. It is a continuation of a previous research paper (Portoles et al., 2011 [1]), which presented test results on eccentrically loaded plain concrete columns. The test parameters are nominal strength of concrete (30, 90 and 130 MPa), eccentricity e (0, 20 and 50 mm) and type of reinforcement. A comparison with the corresponding empty tubular columns is performed, as the aim of the paper is to analyze the influence of each type of infill and establish the best option for practical application. For the limited cases analyzed the results show that the addition of high or ultra-high strength infill is more useful for concentric loaded cases than for eccentric loaded ones, where it seems that the best design option is the utilization of bar reinforced concrete filling rather than steel fiber to reinforce CFST columns. The experimental ultimate load of each test was compared with the design loads from Eurocode 4, accurate for the eccentrically loaded tests.     

钢管超高强混凝土长柱及偏压柱的性能与极限承载能力的研究

本文报导了钢管超高强混凝土长柱和偏压柱的试验研究工作。长柱试验研究结果表明,钢管超高强混凝土长柱的承载能力和极限纵向变形率随长细比Ｌｅ／ Ｄ的增大而下降,在所研究的 Ｌｅ／ Ｄ范围内,所有的钢管超高强混凝土长柱都有一定的延性,但延性随Ｌｅ／Ｄ的增大而降低。普通钢管混凝土长柱的承载能力考虑长细比影响的折减系数计算公式也适用于钢管超高强混凝土长柱。偏压柱试验研究结果表明,在偏心率为０．２２～０．６５范围内,加载后所有偏压柱试件横向无明显的外形变化。在相同的长细比下,随着偏心率的增加,试件的承载能力降低,极限纵向变形率降低,但总体来说,偏压短柱的纵向变形率比轴压短柱的极限应变要大一些。在相同的偏心率下,长细比越大,试件的承载能力和纵向变形率也越低。钢管超高强混凝土耐偏压能力等于或优于普通钢管混凝土偏压柱。经过适当修正的普通钢管混凝土偏心率折减系数可以用于钢管超高强混凝土偏压柱承载能力计算。     

不同加载路径下钢筋混凝土框架柱抗震性能的试验研究

本文对九根不同轴压比的钢筋混凝土悬臂柱进行了不同加载路径下静力周期反复荷载的试验研究。加载路径有单八字形、方形和圆形三种,并对变轴力加载情况作了初步探讨。主要讨论了加载路径和轴压比对构件强度和延性等抗震性能的影响。试验结果表明:加载路径对柱的强度和延性以及钢筋的粘结滑移等有明显影响;柱内存在明显的双轴耦合作用;变轴力加载使柱的延性和刚度比定轴力加载有所下降。     

Experimental study of high strength concrete-filled circular tubular columns under eccentric loading

The paper describes 37 tests conducted on slender circular tubular columns filled with normal and high strength concrete subjected to eccentric axial load. The test parameters were the nominal strength of concrete (30, 70 and 90 MPa), the diameter to thickness ratio D/t, the eccentricity ratio e/D and the column slenderness (L/D). The experimental ultimate load of each test was compared with the design loads from Eurocode 4, which limits the strength of concrete up to 50 MPa. The aim of the paper is to establish the advisability of the use of high strength concretes as opposed to that of normal strength concretes by comparing three performance indices: concrete contribution ratio, strength index and ductility index. The results show for the limited cases analyzed that the use of high strength concrete for slender composite columns is interesting since this achieves ductile behavior despite the increase in load-carrying capacity is not greatly enhanced.     

柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。     

低周反复荷载下型钢高强混凝土柱受力性能试验研究

通过20个混凝土强度为65.3～84.9MPa的型钢高强混凝土柱的低周反复加载试验,研究型钢高强混凝土柱在压、弯、剪共同作用下的破坏形态和抗震性能。试验中考虑剪跨比、轴压比、配箍率、混凝土强度4个参数的影响,由试验获得型钢高强混凝土柱的主要破坏形态和滞回曲线,分析各参数对构件延性、滞回特性、耗能性能以及承载力衰减的影响。结果表明,与型钢普通强度混凝土柱一样,在压、弯和反复剪力共同作用下,型钢高强混凝土柱的破坏形态主要为弯曲型破坏、剪切黏结破坏、剪切斜压破坏,破坏形态主要与剪跨比有关;箍筋能显著提高大剪跨比试件的延性和耗能能力,但对小剪跨比试件的延性与耗能性能改善有限;随着轴压比与混凝土强度的提高,试件的承载力衰减速度加快,后期变形能力减小,抗震性能越来越差;与钢筋混凝土柱相比,型钢高强混凝土柱的等效阻尼比远大于前者,耗能能力强,抗震性能好;提出型钢高强混凝土柱位移延性系数的计算公式,公式的计算结果与试验结果符合较好,可供工程设计应用参考。     

钢管混凝土柱、RC梁板节点拟静力三向加载试验研究

在广州好世界广场超高层建筑工程中设计应用钢管高强混凝土柱的工程实践基础上 ,综合设计 8种钢管混凝土柱、RC梁板节点 ,进行拟静力三向加载试验 ,研究各种节点的受力性能及破坏形态 ,得到了一些有益的结论。     

钢筋混凝土Z形截面双向受剪柱抗震性能试验研究

为研究钢筋混凝土Z形截面双向受剪柱的抗震性能,对4个缩尺比为1/2的试件进行拟静力试验,分析不同水平加载方向（加载角α分别取0°、45°、90°、135°）对其抗震性能的影响,研究Z形截面柱的破坏形态,得到试件的荷载-位移滞回曲线、骨架曲线、承载力、位移延性系数、刚度退化和耗能能力等力学性能指标。研究结果表明：试件在水平反复荷载作用下的破坏形态为弯剪破坏、弯曲破坏、剪切黏结破坏和剪切斜压破坏,其中剪切破坏的试件延性较差;双向水平荷载作用方向对Z形截面柱受剪承载力的影响近似符合椭圆规律,在加载角为45°时,试件的耗能能力最强,当加载角为0°和135°时,试件的耗能能力相差不大。提出钢筋混凝土Z形截面柱双向受剪承载力的计算方法,按该方法对本次试验和已有试验共22个试件进行计算,计算结果与试验值吻合较好。     

大长细比钢筋混凝土细长柱承载力试验研究

通过对8根长细比为20~25的钢筋混凝土细长柱极限承载能力试验,研究了在大长细比区域柱子的长细比、配筋率、混凝土强度等对钢筋混凝土细长柱的极限承载能力及破坏形态的影响。试验结果表明,在大长细比区域,长细比的增加对构件的极限承载力降低效应更加显著;当长细比达到25后,宜采用模型柱法进行设计,偏心距增大系数法设计所增加的纵筋配筋率对提高构件极限承载力的作用不大;但混凝土的强度等级仍然对试件的承载力及破坏形态有较大影响,当混凝土强度接近或大于C60时,即使是长细比为25的构件也可能发生失稳破坏。