Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

Concrete-Filled Steel Tube Arch Bridges in China

In the past 20 years, great progress has been achieved in China in the construction of concrete-filled steel tube （CFST） arch bridges and concrete arch bridges with a CFST skeleton. The span of these bridges has been increasing rapidly, which is rare in the history of bridge development. The large-scale construction of expressways and high-speed railways demands the development of long-span arch bridges, and advances in design and construction techniques have made it possible to construct such bridges. In the present study, the current status, development, and major innovative technologies of CFST arch bridges and concrete arch bridges with a CFST skeleton in China are elaborated. This paper covers the key con- struction technologies of CFST arch bridges, such as the design, manufacture, and installation of steel tube arch trusses, the preparation and pouring of in-tube concrete, and the construction of the world＇s longest CFST arch bridge-the First Hejiang Yangtze River Bridge. The main construction technologies of rein- forced concrete arch bridges are also presented, which include cable-stayed fastening-hanging cantilever assembly, adjusting the load by means of stay cables, surrounding the concrete for arch rib pouring, and so forth. In addition, the construction of two CFST skeleton concrete arch bridges-the Guangxi Yongning Yong River Bridge and the Yunnan-Guangxi Railway Nanpan River Bridge--is discussed. CFST arch bridges in China have already gained a world-leading position; with the continuous innovation of key technologies, China will become the new leader in promoting the development of arch bridges.

Axial Bearing Capacity of Short FRP Confined Concrete-filled Steel Tubular Columns

The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined with fiber-reinforced polymer （FRP） wraps. Totally 11 short column specimens were tested to failure under axial compression. The influences of the type and quantity of FRP, the thickness of steel tube and the concrete strength were studied. It was found that the bearing capacity of short FRP-CFST column was much higher than that of comparable CFST column. Furthermore, the formulas for calculating the bearing capacity of the FRP-CFST columns are proposed. The analytical calculated results agree well with the experimental results.

A simplified model to predict blast response of CFST columns

In order to study the dynamic response of concrete-filled steel tube(CFST) columns against blast loads,a simplified model is established utilizing the equivalent single-degree-of-freedom(SDOF) method,which considers the non-uniform distribution of blast loads on real column and the axial load-bending moment(P-M) interaction of CFST columns.Results of the SDOF analysis compare well with the experimental data reported in open literature and the values from finite element modeling(FEM) using the program LS-DYNA.Further comparisons between the results of SDOF and FEM analysis show that the proposed model is effective to predict the dynamic response of CFST columns with different blast conditions and column details.Also,it is found that the maximum responses of the columns are overestimated when ignoring the non-uniformity of blast loads,and that neglecting the effect of P-M interaction underestimates the maximum response of the columns with large axial load ratio against close range blast.The proposed SDOF model can be used in the design of the blast-loaded CFST columns.

内配型钢的圆钢管混凝土轴压构件的耐火性能

在钢管混凝土构件中内置型钢可有效提高整个构件的承载力和耐火性能。采用ABAQUS软件建立了标准火灾下内配型钢的圆钢管混凝土轴压构件的热力耦合数值模型,并与已有研究者完成的试验数据进行了对比验证;在此基础上,计算了火灾作用下该类构件柱顶轴向位移和跨中挠度随升温时间变化的关系曲线,根据破坏特征可以分为升温初期膨胀阶段、轴向压缩阶段和破坏阶段,并确定了该类构件的耐火极限;最后计算了火灾作用下每个组件间的相互作用力和参数分析。结果表明:随着温度的升高,钢管与混凝土、混凝土与型钢之间的接触应力呈降低趋势;火灾荷载比、长细比、钢管含钢率及防火保护层厚度对构件耐火极限影响较为显著。

内配型钢方钢管混凝土柱非均匀受火的耐火性能

在实际工程中,由于柱所处位置的不同,会形成单面受火、相对或相邻两面受火和三面受火等非均匀的受火边界条件。采用ABAQUS软件,计算了内配型钢方钢管混凝土柱非均匀受火时的温度场和耐火极限,发现非均匀受火时由于温度场分布的不均匀将会产生附加偏心距和附加挠度,其受火性能有别于均匀受火;同时,还计算了构件跨中接触应力和参数的变化。结果表明,柱的截面尺寸和细长比对柱的非均匀火承火能力影响较为显著。

内配型钢矩形钢管混凝土轴压短柱生命周期内的力学性能

为了研究内配型钢矩形钢管混凝土轴压短柱在生命周期内的受力机理,利用有限元软件ABAQUS建立该类短柱的计算模型,并与已有的相关试验结果进行对比。模型中将钢管初应力和长期荷载作为生命周期内的主要因素进行考虑,分析了内配型钢矩形钢管混凝土轴压短柱生命周期内的荷载-变形全过程曲线、跨中截面各部件纵向应力分布和钢材与混凝土之间的相互作用力;考察了初应力系数、长期荷载比和含钢率对构件承载力和变形的影响规律。结果表明:考虑钢管初应力和长期荷载作用的内配型钢矩形钢管混凝土轴压短柱极限承载力与一次加载情况下相比变化不明显,但极限承载力对应的纵向应变增长84.2%;在长期持荷阶段,核心混凝土发生卸载现象,其承担的荷载下降了30%左右,再加载阶段又继续承载;钢管与混凝土之间的接触应力在中截面处最大,沿构件长度方向逐渐向两端减小;随着钢管含钢率增大,构件极限承载力增大,变形减小,而型钢含钢率对构件变形影响较小;随着初应力系数和长期荷载比的增大,构件纵向变形增大。

预制钢管混凝土叠合柱与PEC梁螺栓连接节点受力性能分析

为了揭示预制钢管混凝土叠合柱与预制部分包裹混凝土(PEC)梁螺栓连接节点的受力性能和破坏模式,通过ABAQUS有限元软件建立了该组合节点的有限元分析模型,考虑了材料本构关系和复杂接触问题。通过水平低周往复荷载试验验证了数值分析模型的准确性,对其破坏模式和骨架曲线进行了研究。考虑了几何参数、材料参数、荷载参数对节点力学性能的影响,揭示了多种参数对于节点性能的影响规律。结果表明,预制钢管混凝土叠合柱与预制部分包裹混凝土组合梁全螺栓节点具有良好的受力性能,柱钢材强度、柱混凝土强度、轴压比、螺栓直径及柱截面含钢率对节点的抗弯承载力影响较大;柱混凝土强度、轴压比及柱截面含钢率对节点的初始刚度影响较大。研究结果将为此类节点的分析与设计提供科学依据。

钢管混凝土中型钢与混凝土黏结性能试验研究

为研究钢管混凝土中型钢与混凝土之间的黏结性能,通过21个钢管混凝土中型钢的拔出试验,探究了型钢的黏结长度、截面积、形状等因素的影响。试验结果表明,型钢拔出的极限荷载和破坏后的水平残余荷载都随着黏结长度的增加而增加。对于特定截面尺寸的型钢,型钢与混凝土之间存在一个有效黏结长度,实际黏结长度超过有效黏结长度之后则可保证型钢与混凝土协同工作,破坏模式由型钢的拔出控制转变为由型钢的屈服控制。对于形状相同的型钢,型钢和混凝土之间的极限平均黏结强度和剩余平均黏结强度均与黏结长度关系不大。型钢的形状对于其黏结强度也有一定的影响,型心位置相同的十字形型钢与混凝土的黏结性能优于角钢与混凝土的黏结性能。

火灾后内配H型钢的矩形钢管混凝土柱剩余承载力有限元分析

该文采用ABAQUS有限元软件建立了火灾后内配H型钢的矩形钢管混凝土柱模型,计算了常温下与火灾后该构件的轴向荷载-位移关系曲线,对火灾后的受力性能进行了分析;此外与相同含钢率的钢管混凝土柱构件火灾后剩余承载力进行了对比,发现内配型钢钢管混凝土柱剩余承载力较钢管混凝土柱得以增强,且构件延性优于钢管混凝土;同时对比了强、弱轴两种加载方式下该类构件火灾后剩余承载力,最后对影响火灾后该类构件剩余承载力的主要因素进行了参数分析,发现升温时间、截面周长和长细比对其影响较为显著。

内配型钢方钢管混凝土轴压短柱力学性能及参数分析

在钢管混凝土构件内部配置型钢可显著提高其承载能力和延性等性能。在合理选取材料本构模型的基础上,用ABAQUS软件建立了内配型钢的方形钢管混凝土轴压短柱受力全过程分析的数值模型,数值计算结果和已有研究者完成的试验结果吻合良好,基于此模型对其在轴压受力全过程中各部件的荷载分配进行了分析。在工程常用参数范围内对影响其荷载-变形曲线的主要因素进行了参数分析,结果表明:随着钢管强度、型钢强度、混凝土强度、钢管和型钢截面含钢率的提高构件的极限承载力有所提高。参数分析的结果上可为进一步明晰该类组合构件工作机理和确定承载力指标等提供基础。

内置十字钢骨圆钢管混凝土构件受弯性能有限元分析

在合理选取钢材和混凝土材料本构关系模型的基础上,采用有限元分析软件ABAQUS对部分圆形截面的钢管混凝土受弯构件以及2个内置十字钢骨圆钢管混凝土构件的受弯性能试验进行有限元模拟,并设计内配十字钢骨圆钢管混凝土受弯构件,研究其在荷载作用下的受力特征,并进行混凝土强度、钢管及钢骨屈服强度、钢管及钢骨截面含钢率等参数分析。结果表明:典型受弯构件的挠度曲线近似为正弦半波曲线;弯矩-曲率曲线大致可分为弹性段、弹塑性段和塑性强化段;钢管截面含钢率对构件受弯承载力的影响比较显著,型钢材料强度对其影响很小。

长期荷载作用下内置钢骨钢管混凝土轴压短柱受力性能研究

基于合理材料本构模型,本文利用有限元软件ABAQUS首先建立了考虑长期荷载作用时钢管混凝土轴压柱数值分析模型,在模型验证的基础上,进行考虑长期荷载作用时内置十字形钢骨圆钢管混凝土轴压柱受力全过程分析,同时与不考虑长期荷载作用时的结果进行对比,最后对长期荷载比、徐变终值系数、持荷时间、加载龄期4个典型影响因素进行了分析。结果表明:考虑长期荷载作用影响的组合柱极限承载力略大于不考虑长期荷载作用的情况,但其极限承载力所对应的应变却比不考虑长期荷载时大;考虑长期荷载作用时轴压柱的极限承载力随着徐变终值系数、持荷时间的增长而略有提高,而长期荷载比、加载龄期对其几乎没有影响。

施工初应力与长期荷载作用下内配型钢的方钢管混凝土轴压柱受力性能研究

为研究内配型钢的方形钢管混凝土构件在施工初应力和长期荷载作用下的力学性能,基于合理的材料本构,采用有限元软件ABAQUS建立了考虑这两种荷载作用的有限元模型,通过相关试验验证了模型的有效性。在此基础上,对典型内配型钢的方形钢管混凝土柱分析了该类构件各部件间受力机理和破坏形态,并分别与其一次加载时以及方钢管混凝土考虑初应力和长期荷载作用时的承载力变化进行了对比。结果表明:考虑施工初应力和长期荷载后,构件在施工初应力和长期加载阶段产生了初变形;在长期持荷阶段,主要由钢管和型钢受力,构件整体徐变率较小;而再加载阶段,主要由混凝土受力。与一次加载相比,初应力和长期荷载作用下构件承载力增大不显著,但与未配型钢的钢管混凝土相比,承载力增大明显;型钢的存在有效约束了混凝土横向的膨胀变形。