Concrete-filled double skin (SHS outer and CHS inner) steel tubular beam-columns

A series of tests on concrete-filled double skin steel tubular (CFDST) stub columns (14), beams (four) and beam-columns (12) were carried out. The specimens had square hollow section (SHS) as outer skin and circular hollow section (CHS) as inner skin. A mechanics model is developed in this paper for the CFDST stub columns, columns and beam-columns. A unified theory is described where a confinement factor (ξ) is introduced to describe the composite action between the steel tubes and the sandwiched concrete. The load versus axial strain relationship for CFDST stub columns is predicted. Simplified model is derived for section capacities of CFDST. The predicted beam-column strength is compared with that obtained in beam and beam-column tests. The load versus mid-span deflection relationship for CFDST beams and beam-columns is predicted. A simplified model is developed for calculating the member capacity of the CFDST beams. Simplified interaction curves are derived for CFDST beam-columns.     

Plastic mechanism analysis of concrete-filled double-skin (SHS inner and SHS outer) stub columns

A plastic mechanism to predict the collapse behaviour of concrete-filled double-skin stub columns is developed and analysed in this paper. Both outer and inner tubes are square hollow sections (SHS). In the analysis, the inner tube is treated the same way as that used in previous research on empty SHS stub columns. New mechanism models are developed for the outer tubes. The effect of local buckling in the outer tube is also studied. The concrete model adopted in this paper considers the effect of confinement of the concrete induced by the double skin tubes. It also considers the strength degradation of concrete for large deformation analysis. It has been found that the effect of local buckling on the collapse curve of the outer tube can be ignored. The concrete model including confinement and strength degradation should be used in order to simulate the collapse behaviour, especially for thin outer tubes. Good agreement was achieved between the plastic mechanism analysis and experimental results.     

Tests on stub stainless steel-concrete-carbon steel double-skin tubular (DST) columns

A new type of composite member, a stainless steel-concrete-carbon steel double-skin tubular (DST) column, is introduced in this paper. This composite member is expected to combine the advantages of all three types of materials, and have additional advantages of esthetics and resistance to corrosion that outer stainless steel offers. A series of tests are performed to investigate the performance of the composite column, and a total of 80 specimens were tested. The main parameters of the tests are the sectional type (circular, square, round-end rectangular and elliptical), the column type (straight, inclined and tapered), and the hollow ratio of the composite section (from 0.5 to 0.75). The results show that all types of columns behaved in a ductile manner, and the mechanical behavior is similar to those columns with double carbon steel tubes. A simplified model for the prediction of the stainless steel-concrete-carbon steel double-skin tubular (DST) columns cross-sectional strengths is suggested as well.     

方中空夹层钢管混凝土柱滞回性能研究

以轴压比和空心率为主要参数,进行了12个方中空夹层钢管混凝土试件和4个方实心钢管混凝土试件滞回性能的试验研究。试验表明:方中空夹层钢管混凝土和方实心钢管混凝土荷载-位移滞回曲线饱满,其延性明显优于空钢管试件;轴压比越大的试件,初始刚度越大,但刚度后期退化越快。比较了国内外较典型的几种设计规范(程)对试件抗弯刚度的计算,结果表明,AISC-LRFD(1999)、EC4(1994)、BS5400(1979)、DBJ 13-51(2003)的计算结果与实测的初始抗弯刚度较吻合,DBJ 13-51(2003)的计算结果与实测的使用阶段抗弯刚度最接近。在确定了钢材和混凝土的本构关系的基础上,采用数值方法对荷载-位移滞回曲线进行了计算,理论计算结果与试验结果较吻合。最后分析了轴压比、空心率、长细比、名义含钢率、材料强度等参数对荷载-位移骨架曲线的影响。     

组合T形截面钢管混凝土柱偏心受压试验研究

在分析各种异形钢管混凝土柱工程应用的基础上,提出组合T形截面钢管混凝土柱。考虑长细比、偏心距等参数的影响,设计制作18个组合T形钢管混凝土柱试件。通过偏心受压试验,对长细比16.0<λ≤28.8的组合T形钢管混凝土柱压弯性能进行研究,考察试件的破坏形态,实测试件的荷载-应变曲线和荷载-柱中挠度曲线,分析各参数对试件偏心受压力学性能的影响。通过试验数据回归分析,参考国内外相关规范,提出组合T形截面钢管混凝土柱偏心受压承载力计算公式。试验结果表明：偏心受压柱均为弯曲失稳破坏,长细比越大,弯曲破坏特征越明显;偏心距越大,试件极限承载力越低。研究表明,组合T形钢管混凝土柱的两个组成部分能很好地协同工作,力学性能较好;所提出的承载力计算公式可供工程设计参考。图10表3参8     

Experimental and computational study of concrete filled steel tubular columns under axial loads

The paper presents an experimental and computational study on the behaviour of circular concentrically loaded concrete filled steel tube columns till failure. Eighty-one specimens were tested to investigate the effect of diameter and D/t ratio of a steel tube on the load carrying capacity of the concrete filled tubular columns. The effect of the grade of concrete and volume of flyash in concrete was also investigated. The effect of these parameters on the confinement of the concrete core was also studied. Diameter to wall thickness ratio between 25<D/t<39, and the length to tube diameter ratio of 3<L/D<8 was investigated. Strength results of Concrete Filled Tubular columns were compared with the corresponding findings of the available literature. Also a nonlinear finite element model was developed to study the load carrying mechanism of CFTs using the Finite Element code ANSYS. This model was validated by comparison of the experimental and computational results of load-deformation curves and their corresponding modes of collapse. From the experimental and computational study it was found that for both modes of collapse of concrete filled tubular columns at a given deflection the load carrying capacity decreases with the increase in % volume of flyash up to 20% but it again increases at 25% flyash volume in concrete.     

核心高强钢管混凝土柱轴心受压的机理及计算

探讨了核心钢管混凝土柱的工作机理,根据10根核心高强钢管混凝土柱轴心受压的试验分析,提出了核心高强钢管混凝土柱轴心受压承载力的计算公式,并给出了设计建议。     

方中空夹层钢管混凝土柱的承载力及影响因素分析

采用双剪统一强度理论,对轴心受压下的方中空夹层钢管混凝土短柱的受力性能进行了理论分析.引入考虑厚边比影响的等效约束折减系数和混凝土强度折减系数,将方中空夹层钢管混凝土等效为圆中空夹层钢管混凝土,在厚壁圆筒统一强度理论的基础上,结合钢管混凝土统一理论,推导出方中空夹层钢管混凝土柱的极限承载力,并对影响因素进行了分析.与有关文献的试验结果进行比较,结论基本一致,证明统一强度理论对方中空夹层钢管混凝土的理论分析有很好的适用性.该结果为方中空夹层钢管混凝土承载力的分析计算提供了一定的理论依据.     

轴向冲击荷载作用下钢管混凝土短柱有限元分析

利用ANSYS-DYNA进行了钢管混凝土短柱抗冲击性能有限元分析研究,通过分析应力、应变时程曲线,获得对其抗动力冲击性能的了解。构件受力时,外围钢管的应力远远大于内部混凝土的应力;试件应力、应变时程曲线表现出典型弹塑性材料的性质,数值增加到最大值后递减,最终形成残余应力、应变。结果表明,钢管混凝土具有良好的抗冲击力学性能,即具有较高的强度和屈服后承载能力,以及良好的塑性变形能力。     

An experimental study on elliptical concrete filled columns under axial compression

This paper presents the experimental results and observation of elliptical concrete filled tube (CFT) columns subjected to axial compressive load. A total of twenty-six elliptical CFT specimens including both stub and slender composite columns are tested to failure to investigate the axial compressive behaviour. Various column lengths, sectional sizes and infill concrete strength are used to quantify the influence of member geometry and constituent material properties on the structural behaviour of elliptical CFT columns. As there is no design guidance currently available in any Code of Practice, this study provides a review of the current design rules for concrete filled circular hollow sections in Eurocode 4 (EC4). New equations based on the Eurocode 4 provisions for concrete filled circular hollow sections were proposed and used to predict the capacities of elliptical CFT columns.     

Concrete filled steel tube stub columns under combined temperature and loading

A finite element analysis (FEA) model was developed to predict the load versus deformation relationships of concrete filled steel tube (CFST) stub columns subjected to a combination of temperature and axial compression. This model was used to simulate a set of CFST stub column experiments under various thermal and mechanical loading conditions, including tests at high temperature, tests on the residual strength of specimens subjected to uniform heating, and tests on specimens exposed to the ISO-834 standard fire without initial loads. Comparisons between the predicted results and the test results show that this model can predict the load versus deformation relationships with reasonable accuracy. The FEA model was then used to investigate the behaviour of CFST stub columns in a complete loading history including initial loading, heating and cooling by examing the cross-sectional stress distribution and confinement stress development at different loading phases. All specimens were loaded to ultimate strength after cooling and the residual stress index was studied with respect to a group of parameters. It can be found that the ultimate strength when considering the mutual actions of temperature and loading was slightly lower than that after exposure to fire without initial load, but the peak strain corresponding to the ultimate strength was increased significantly.     

Numerical analysis of slender elliptical concrete filled columns under axial compression

This paper presents a non-linear finite element model (FEM) used to predict the behaviour of slender concrete filled steel tubular (CFST) columns with elliptical hollow sections subjected to axial compression. The accuracy of the FEM was validated by comparing the numerical prediction against experimental observation of eighteen elliptical CFST columns which carefully chosen to represent typical sectional sizes and member slenderness. The adaptability to apply the current design rules provided in Eurocode 4 for circular and rectangular CFST columns to elliptical CFST columns were discussed. A parametric study is carried out with various section sizes, lengths and concrete strength in order to cover a wider range of member cross-sections and slenderness which is currently used in practices to examine the important structural behaviour and design parameters, such as column imperfection, non-dimension slenderness and buckling reduction factor, etc. It is concluded that the design rules given in Eurocode 4 for circular and rectangular CFST columns may be adopted to calculate the axial buckling load of elliptical CFST columns although using the imperfection of length/300 specified in the Eurocode 4 might be over-conservative for elliptical CFST columns with lower non-dimensional slenderness.     

钢管约束的钢管混凝土短柱轴压性能试验研究

为增强核心混凝土约束作用并改善其力学性能,在钢管混凝土外部增设圆钢管形成钢管约束的钢管混凝土组合柱,以构件类型、内层和外层钢管含钢率及核心混凝土强度等级为参数,设计并完成了14个钢管约束的钢管混凝土短柱和14个钢管混凝土短柱的轴压试验;观察试验现象和不同试件的破坏模式,研究各关键参数对试件轴压力学性能的影响,分析内层和外层钢管应力和应变发展规律,对比分析钢管混凝土和钢管约束的钢管混凝土的承载力和变形性能。研究结果表明:当钢管约束的钢管混凝土套箍系数不小于0.87,可使钢管混凝土柱的剪切脆性破坏转为截面压溃破坏,外观表现为腰鼓形破坏;达到承载力时,外层钢管横向应力可以达到钢材屈服强度,对核心混凝土的约束作用较强;钢管约束的钢管混凝土短柱轴压承载力较含钢率相近的常规钢管混凝土承载力可以提高20%左右,较内部钢管混凝土承载力可提高约70%。基于叠加法和GB 50936—2014《钢管混凝土结构技术规范》,提出两种钢管约束的钢管混凝土轴压承载力计算方法,预测结果与试验结果吻合良好。     

钢管轻集料混凝土中长柱轴压性能的试验研究

通过对20根具有不同长细比和混凝土强度等级的钢管轻集料混凝土中长柱进行轴压试验,研究了钢管轻集料混凝土中长柱在轴心压力下的宏观变形特征、轴力-应变关系、破坏模式和破坏机理,并与钢管普通混凝土的轴压性能进行了对比。研究结果表明:长细比是影响钢管轻集料混凝土中长柱承载力的主要因素,在相同条件下,长细比越大,试件的承载力越低;核心混凝土强度对钢管轻集料混凝土试件的稳定系数有一定影响,在截面参数相同的情况下,核心混凝土强度较高的试件稳定系数比混凝土强度较低的试件要高;在本研究的范围内,钢管轻集料混凝土的稳定系数要高于长细比相同的钢管普通混凝土。     

钢管高强混凝土组合柱轴心抗压数值分析

为研究钢管高强混凝土组合柱的轴心抗压性能,利用高强混凝土和钢管混凝土本构关系,对组合柱轴心抗压受力全过程进行了数值计算,计算轴力-纵向应变曲线与试验结果吻合良好;并与钢筋混凝土柱进行了对比,定量分析了套箍指标、混凝土强度和配箍特征值对轴压承载力和纵向应变延性的影响.     

Experimental study on steel tubular columns in-filled with plain and steel fiber reinforced concrete

An experimental investigation on the structural behaviour of steel tubular columns in-filled with plain and steel fiber reinforced concrete is presented in this study. A total of 16 concrete-filled steel tubular columns were constructed and tested subjected to biaxial bending and short-term axial load. The main variables considered in the test study were the cross section, slenderness, concrete compressive strength and the load eccentricity. In the presented study, a theoretical method for the prediction of ultimate strength capacity and load-deflection curves of concrete filled steel tube columns is proposed. In the analysis procedure, the nonlinear behaviour of the materials is considered and the slenderness effect has been taken into account. The experimental ultimate strength capacities and load-deflection curves of both plain and steel fiber concrete-filled tube columns have been compared with the analysis results and discussed in the paper. The results indicate that the addition of steel fibers in core concrete has considerable effect on the behaviour of concrete-filled steel tube columns.     

波纹侧板-方钢管混凝土柱轴压性能研究

为研究波纹侧板-方钢管混凝土柱轴压性能,进行了1个1/2缩尺试件轴压试验,对其受力机理、破坏模式进行分析,发现该类柱具有较好的延性及较高的承载能力。同时对波纹侧板-方钢管混凝土柱进行了有限元分析,分析结果表明:由于波纹板具有较高的侧向刚度,使核心混凝土能够得到较好的约束,但是波纹板基本不承担轴向荷载;破坏形式为钢管局部屈曲、波纹板向外鼓曲、钢管内混凝土及核心混凝土被压碎;随着波纹板厚度增加,承载力、延性提高;随着波纹板强度提高,延性略有提高,对承载力影响不大;承载力随混凝土强度提高而提高,但是延性变差。提出了波纹侧板-方钢管混凝土柱轴压承载力实用计算式,计算值与有限元分析值、试验值吻合较好。     

碳纤维约束混凝土短柱的强度计算

利用极限平衡法，通过分析加固率对约束混凝土性能的影响，对实验数据进行拟合，导出了碳纤维约束混凝土短柱在轴心受压状态下的抗压强度计算公式，指出碳纤维约束混凝土试件的实验数据与该公式的计算结果吻合较好，且公式形式简单，具有实际应用价值。     

碳纤维约束混凝土短柱强度计算新方法

利用极限平衡法，通过分析加固率对约束混凝土性能的影响，对文献中的实验数据进行拟合，导出了碳纤维约束混凝土短柱在轴心受压状态下的抗压强度计算公式，并引用文献中的实验数据与该公式计算结果进行对比，两者吻合较好。     

Behaviour of concrete filled steel tubular (CFST) stub columns under eccentric partial compression

This paper investigates the behaviour of concrete filled steel tubular (CFST) stub columns subjected to eccentric partial compression. Twenty-eight specimens were tested and presented. The main parameters in test program include: (1) section type: circular, square and rectangular; (2) load eccentricity ratio (including uniaxial and biaxial loading): from 0 to 0.4; and (3) shape of the loading bearing plate (BP): circular, square, strip and rectangular. The test results indicated that, similar to the corresponding fully loaded CFST stub columns under eccentric loading, CFST stub columns under eccentric partial compression have generally reasonable bearing capacity and favorable ductility. A finite element analysis (FEA) model for CFST stub columns under eccentric partial compression is developed and the predicted performances are validated through measured results. The FEA model is then used to investigate the mechanisms of such composite columns further.