Behavior of concrete and concrete-filled circular steel tubular stub columns at constant high temperatures

Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular （CFST） stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.

Numerical analysis of ultimate strength of concrete filled steel tubular arch bridges

The calculation of ultimate bearing capacity is a significant issue in the design of Concrete Filled Steel Tubular (CFST) arch bridges. Based on the space beam theory, this paper provides a calculation method for determining the ultimate strength of CFST structures. The accuracy of this method and the applicability of the stress-strain relationships were validated by comparing different existing confined concrete uniaxial constitutive relationships and experimental results. Comparison of these results indicated that this method using the confined concrete uniaxial stress-strain relationships can be used to calculate the ultimate strength and CFST behavior with satisfactory accuracy. The calculation results are stable and seldom affected by concrete con-stitutive relationships. The method is therefore valuable in the practice of engineering design. Finally, the ultimate strength of an arch bridge with span of 330 m was investigated by the proposed method and the nonlinear behavior was discussed.

Approach for analyzing the ultimate strength of concrete filled steel tubular arch bridges with stiffening girder

A convenient approach is proposed for analyzing the ultimate load carrying capacity of concrete filled steel tubular (CFST) arch bridge with stiffening girders. A fiber model beam element is specially used to simulate the stiffening girder and CFST arch rib. The geometric nonlinearity, material nonlinearity, influence of the construction process and the contribution of prestressing reinforcement are all taken into consideration. The accuracy of this method is validated by comparing its results with experimental results. Finally, the ultimate strength of an abnormal CFST arch bridge with stiffening girders is investigated and the effect of construction method is discussed. It is concluded that the construction process has little effect on the ultimate strength of the bridge.

Flexural Capacity Formula of Diaphragm-Through Joints of Concrete-Filled Square Steel Tubular Columns

Finite element analysis and parametric studies were performed to investigate the flexural capacity of the panel zone of diaphragm-through joints between concrete-filled square steel tubular columns and H-shaped steel beams. Through the comparisons of failure modes, load–displacement curves, and bearing capacity, it was found that the flexural capacity of the panel zone of diaphragm-through joints was determined by the tensile action and influence of the web of H-shaped steel beams, and the axial load should be taken into account. The steel tube and the diaphragm were the major parts of the joint that resisted the bending moment. The contribution of in-filled concrete had little influence on the flexural capacity of the panel zone of the joint and could be neglected. According to the results of these numerical studies, a formula that considered the influence of the web of H-shaped steel beams and the axial load was developed based on the yield lines in the diaphragm and the steel tube. The results of the proposed formula were in good agreement with the numerical data of this investigation. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Influence of Axial Load Ratio on Shear Behavior of Through-Diaphragm Connections of Concrete-Filled Square Steel Tubular Columns

Nonlinear finite element analysis and parametric studies were carried out to study the influence of axial load ratio on the shear behavior of the through-diaphragm connections of concrete-filled square steel tubular columns. The analysis reveals that smaller axial load ratio can improve the shear bearing capacity and ductility while larger axial load ratio will decrease the shear behavior of the through-diaphragm connections. The parametric studies indicate that the axial load ratio should be limited to less than 0.4 and its influence should be considered in the analysis and design of such connections.

Experimental investigation of seismic performance of concrete-filled glass fiber reinforced polymer tubular columns

A reinforced concrete (RC) column and four concrete filled GFRP tubular columns,which are subjected to combined axial compression and lateral cycle loading,were tested in order to investigate the seismic performance of composite construction concrete filled glass fiber reinforced polymer (GFRP) tubular (CFFT) columns.The results indicated that concrete-filled GFRP tubular columns exhibit considerable influence over the seismic performance of columns by providing hoop confinement to the core concrete.The concrete filled GFRP tubular columns exhibit significant improvement over traditional RC columns in both ultimate strength and ductility.Different column-footing connection modes do not affect the strength and ductility of concrete filled GFRP tubular columns.The strength of concrete filled GFRP tubular columns under high axial compression load conditions are slightly increased,however,ductility declined.

In-Plane Creep Buckling of Concrete-Filled Steel Tubular Arches

The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40%

RPC外包方钢管混凝土柱轴压受力性能研究

为了研究活性粉末混凝土(Reactive powder concrete,RPC)外包方钢管混凝土柱的轴压受力性能,以RPC厚度和长细比为参数,对6根构件开展轴压试验研究,探讨该类组合柱的破坏模式、受力机理、套箍效应和承载力。试验结果表明:外层RPC可为内部方钢管混凝土柱提供较强的约束力,在受力后期套箍效应凸显。随着RPC厚度的增加,组合柱的承载力逐渐提高;随着组合柱长细比的增大,虽然其弹性刚度和承载力逐渐降低,但延性改善。采用ABAQUS软件建立RPC外包方钢管混凝土柱的有限元模型,分析RPC强度、RPC厚度、钢管强度等级、含钢率、内部混凝土强度和长细比等参数对组合柱承载力的影响规律,可得方钢管混凝土柱发挥系数的变化幅值为0.78~1.01。在试验研究、有限元参数分析和理论探讨的基础上,借鉴钢管混凝土结构技术规范,提出了RPC外包方钢管混凝土轴压短柱和长柱的承载力简化计算方法,公式计算值与已有数据样本吻合良好。

钢管混凝土键连接框架梁和剪力墙的受剪性能

目的 研究钢管混凝土键连接框架梁和剪力墙的受剪性能,为工程应用提供设计依据。方法 应用有限元分析软件ABAQUS对比钢管混凝土键连接与现浇连接梁墙的结构受剪性能,分析前者受剪机理及不同因素对受剪性能的影响。结果 钢管混凝土键连接梁墙的结构承载力和延性系数较现浇结构分别提高约10%和34%;钢材强度从Q235到Q390,初始刚度增加8.44%;截面高度从100 mm到120 mm,延性系数提高17.73%;截面厚度每增加2 mm,承载力提高约15%;截面长度和混凝土强度等级对承载力、初始刚度和延性系数的影响均小于15%,纵向距离对其受剪性能几乎无影响。结论 采用钢管混凝土键连接梁墙的结构总体受剪性能优于现浇结构;钢材强度和截面厚度分别是影响初始刚度和承载力的主要因素。

新型钢管混凝土梁柱节点力学性能试验研究

为研究内加强环式圆钢管混凝土柱与矩形钢管混凝土梁这种新型连接节点的力学性能,设计了缩尺钢管混凝土梁柱节点试件,开展了相同梁柱节点试件的静力加载试验和低周往复加载试验。通过研究该节点试件的破坏模式、荷载-位移曲线以及拟静力加载试验的骨架曲线、核心区剪切变形等,分析了节点试件的承载能力、延性和耗能能力,全面考察了同一梁柱节点在静力加载和低周往复加载两种工况下的受力性能和破坏模式。结果表明:钢管混凝土梁柱节点试件核心区强度较强,破坏模式主要为梁端破坏,低周往复加载试验时试件梁柱连接处附近的梁端钢板发生拉裂破坏和钢板鼓曲,静力加载试验时试件梁端焊缝发生拉裂破坏;试件延性较好,加载过程中经历了弹性、弹塑性和塑性发展阶段。最后提出了该类钢管混凝土梁柱节点核心区的抗剪强度计算公式。

反复荷载下方钢管型钢再生混凝土组合柱抗震性能试验研究

为研究方钢管型钢再生混凝土组合柱的抗震性能,通过对9个组合柱试件进行低周反复荷载试验,对其地震破坏特征进行分析,并详细探究再生粗骨料取代率、型钢配钢率、方钢管宽厚比和轴压比等影响参数对组合柱承载力、延性及耗能能力等抗震性能指标的影响。研究结果表明:在反复水平荷载作用下组合柱呈现典型的压弯塑性铰破坏模式。组合柱的荷载-位移滞回曲线呈饱满“纺梭形”,具有较好的耗能能力。再生粗骨料取代率对组合柱的承载力的影响较小,随着再生粗骨料取代率的增加,组合柱的延性和耗能能力逐渐下降,延性和耗能能力最大分别下降7.83%和7.6%,组合柱试件承载力先升高后下降,承载力最大变化幅值为1.98%,影响幅值较小。随着方钢管宽厚比的减小或型钢配钢率的提高,组合柱的承载力和延性均得到提高,宽厚比从100降至33,承载力提高了57.44%,而型钢配钢率从4.2%增长至6.3%,承载力和延性则分别提高了21.45%和20.44%,说明方钢管宽厚比和型钢配钢率对组合柱抗震性能影响较大。另外,增大轴压比对组合柱试件的抗震性能不利,随着轴压比的增大,组合柱的滞回曲线饱满度下降,延性降低,轴压比从0.2提高到0.6,延性降低了11.11%。研究结论可为方钢管型钢再生混凝土组合柱的抗震设计提供参考。

集中荷载作用下弹性支撑矩形钢管混凝土翼缘工字形梁稳定性能研究

为研究弹性支撑刚度对矩形钢管混凝土翼缘工字形梁稳定性能的影响,开展了集中荷载作用下3根带有不同弹性支撑刚度的矩形钢管混凝土翼缘工字形梁的稳定性能试验,研究试验梁的位移及应变的变化规律,获得梁的失稳形式和稳定承载力。试验结果表明,整个加载破坏过程分为三个阶段,即弹性阶段、弹塑性阶段和破坏阶段,3根试验梁均发生整体弯扭屈曲失稳。随着弹性支撑刚度增加,梁稳定承载力增大,验证了设置弹性支撑可有效地提高该梁的稳定承载力。在试验基础上,利用ANSYS有限元软件对该梁进行非线性屈曲分析,将获得的稳定承载力与试验结果进行对比,误差均小于5%,从而验证有限元分析方法的正确性。最后,研究了混凝土强度、上翼缘含钢率和腹板高厚比等参数对该类梁稳定性能的影响规律。研究表明,增大上翼缘钢管含钢率和减小腹板高厚比均可明显提高该类梁的稳定承载力,而增强混凝土强度对梁的稳定承载力提高较小。

薄壁钢板局部屈曲关键问题研究进展

钢结构以及钢-混凝土组合结构由于其强度高、耗能能力好、施工方便等优异性能,被广泛应用于工程结构中。然而,随着高强度钢材的应用,薄壁钢板呈现薄壁化、宽厚比随着构件截面尺寸的增大而不断增大的趋势,由于工程结构及荷载的复杂性等因素,钢板过早发生局部屈曲的风险不断加大,薄壁钢板的局部屈曲问题凸显,亟待开展系统性深入研究。对薄壁钢板局部屈曲研究的进展进行了概述,分析总结了现有试验研究和理论研究方面存在的局限性,详细介绍了笔者团队近年来聚焦于薄壁钢板局部屈曲关键问题开展的一系列研究工作及成果。

高寒环境温度下钢管混凝土柱抗震性能试验研究

为探究高寒地区环境温度对圆钢管混凝土柱抗震性能的影响,开展4种不同温度工况下钢管混凝土柱的拟静力试验研究,分析不同环境温度下各试件的破坏特征、承载力、滞回特性、刚度退化、延性及耗能能力,揭示环境温度变化对钢管混凝土柱抗震性能的影响规律。试验结果表明:不同环境温度下各试件滞回曲线均呈梭形,未产生明显捏缩现象;试件典型破坏模式在不同温度下基本一致,均为钢管底部产生一圈贯通鼓曲波、核心混凝土被压溃、钢管撕裂,温度越低,钢管混凝土柱越早发生破坏,且破坏程度越严重;相较于常温(20℃)工况,0℃、-20℃、-40℃温度工况下,试验钢管混凝土柱水平承载力分别提高3.08%、6.15%、10.08%,初始刚度分别提高16.9%、30.3%、50.0%,而延性系数分别降低8.6%、14.6%、16.9%;环境温度越低,刚度退化速率也越大。温度变化对钢管混凝土柱抗震性能影响显著,高寒地区钢管混凝土结构抗震设计时需考虑环境低温对结构带来的不利影响。

大高宽比矩形钢管混凝土柱压弯性能研究

为了研究大高宽比矩形钢管混凝土柱的压弯性能,对大高宽比钢管混凝土短柱进行偏压试验并结合有限元模拟补充了4组试件进行对比,包括不同偏心率、高宽比、钢管壁厚度、截面尺寸情况下柱性能的对比分析。最后参考常用的4本国内外规范进行柱承载力计算,对比并判断现有规范是否适用。结果表明:试件破坏模式均为长边鼓曲,当荷载小于极限承载力的80%时,横截面高度上的应变分布服从平截面假定;随着偏心率增大,柱延性提升,在偏心率超过0.205后,柱延性开始下降;随着壁厚增加,柱延性提升,在壁厚达到8 mm后,柱延性开始下降;随着高宽比提升,柱延性降低;随着截面尺寸增大,在壁厚不变的情况下,柱延性降低,在壁厚等比例增大时,柱延性变化不大;随着高宽比、截面尺寸、钢管壁厚度的增大,柱承载力提升;随着偏心率升高,柱承载力降低;参考规范JGJ 138—2016对大高宽比钢管混凝土柱偏压承载力的计算更为准确。

内置H型钢的圆铝管混凝土短柱轴压性能分析

为研究内置H型钢的圆铝合金管混凝土短柱的轴压力学性能及受力机理,采用ABAQUS建立了该类试件的有限元模型,在有限元验证基础上,研究了试件在轴向荷载作用下的破坏形态,对典型试件进行了受力全过程分析以及接触力分析,研究了试件不同高度处的截面各组成部分的荷载分担情况,总结了试件各部分之间接触应力的变化规律;研究了混凝土抗压强度、含钢率、铝合金管壁厚以及截面构造对试件轴压力学性能的影响。结果表明:试件在轴向荷载作用下铝合金管、混凝土以及H型钢表现出良好的组合效应,通过参数分析发现,轴压短柱受力过程中的横向变形随着混凝土立方体抗压强度增大而增大,参数分析中圆铝合金管壁厚对轴压短柱的承载能力影响最大。可见内置H型钢的圆铝合金管混凝土柱组合构件在受轴向荷载时表现出较强的承载能力以及良好的抵抗变形能力。

钢管高强再生混凝土叠合柱偏压性能

为研究钢管高强混凝土叠合柱偏心受压性能,以混凝土类型和偏心距为参数,完成了6根叠合柱偏心受压试验,研究了不同参数对钢管高强混凝土叠合柱损伤发展过程、破坏特征、承载力和延性的影响,并基于《钢管混凝土叠合柱结构技术规程》(T/CECS 188—2019)和相关学者提出的公式对16根钢管混凝土叠合柱的偏压承载力进行了计算。研究结果表明:再生混凝土叠合柱与普通混凝土叠合柱的受力过程均经历了弹性、带裂缝工作和破坏3个阶段,表现出外围混凝土保护层被压碎脱落、纵筋鼓曲和箍筋外鼓等破坏特征;与普通混凝土叠合柱相比,再生混凝土叠合柱的初始刚度和变形能力有所降低,但承载力略高;随着偏心距的增加,钢管混凝土叠合柱的初始刚度和承载力迅速降低,而位移延性系数迅速增大,中和轴逐渐向受压区移动,与平截面假定的吻合度有所降低;钢管混凝土叠合柱偏压承载力计算应考虑钢管自身承载力以及钢管对核心混凝土约束效应的影响。

内置碳钢不锈钢管海洋混凝土柱轴压试验及承载力计算

为研究不锈钢管海洋混凝土柱及内配碳钢后的轴压力学性能,以型钢类型、螺旋筋间距、纵筋直径为变化参数,完成了10个试件的轴心受压静力加载试验。观察了试件的受力破坏全过程及形态,获取了轴向荷载-位移曲线及各钢材应变曲线,基于试验实测数据,就各变化参数对试件的轴压承载力、延性、耗能能力和损伤发展的影响规律进行了分析。结果表明:不同试件的破坏形态相似,均表现为不锈钢管局部屈曲压皱,混凝土斜向剪切破坏;内置碳钢可以提高试件的极限承载力、轴压延性和耗能能力,抑制试件的损伤发展;在增加相同用钢量的条件下,增加圆钢管含钢量对试件轴压性能提升幅度最大;基于“复合约束叠加法”推导计算公式所得承载力计算值与试验值吻合良好。

圆钢管砖骨料地聚物再生混凝土柱滞回性能试验研究

为探究废弃黏土砖再利用的可行性,对6根圆钢管砖骨料地聚物再生混凝土柱的滞回性能进行了系列试验研究。以不同钢管厚度(4、6 mm)、砖骨料取代率(0%、50%、100%)、轴压比(0.05、0.25、0.50)为参数,得到了试件在往复荷载作下的失效模态、骨架曲线和滞回曲线,并对构件的刚度退化、滞回性能、峰值承载力、延性、承载力退化和耗能能力等抗震性能指标的变化规律分析。结果表明:试件的失效模式表现为底部发生鼓曲、开裂,出现塑性铰的区域核心混凝土破碎,与普通钢管混凝土相似;砖骨料取代率和轴压比的增加会降低试件的承载力,钢管厚度的增加会提高试件的承载力。试件的滞回曲线饱满,表现出不明显的捏缩,表明耗能能力较好;轴压比的增加导致试件的变形能力降低,加快了刚度和承载力的退化速度,增长钢管厚度可以提高试件的变形能力;砖骨料取代率对试件刚度退化、延性、承载能力和耗能能力的影响有限。