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.     

L形截面钢纤维高强钢筋混凝土柱及复合柱偏心加载试验

研究钢纤维对L形截面高强钢筋混凝土柱和混凝土复合柱的性能的影响。对16根L形截面钢纤维柱进行试验研究。主要参数为混凝土抗压强度、荷载偏心率、长细比影响以及钢纤维含量。对L形截面钢筋混凝土柱的试验结果进行了讨论。此外,基于材料的非线性特性对试样进行了分析。采用ACI318规范中的弯矩放大法对长细比影响加以考虑。结果表明:高强混凝土中加入钢纤维能够增强L形截面钢筋混凝土柱和复合柱的结构特性,有利于抵抗双向弯曲和轴向加载。     

Influence of corrosion on the ultimate compressive strength of steel plates and stiffened panels

This study concentrates on a comparison between steel plate and stiffened panels subject to localised corrosion. A finite element analysis is used to investigate the effect of random corrosion on the compressive strength capacity of marine structural units. Variables include the extent of corrosion; slenderness ratio and aspect ratio. A corrosion prediction model is incorporated to determine the thickness reduction with time. Corrosion-induced volume loss results in a greater reduction of ultimate strength for slender plates compared to stiffened panels, up to 45%, showing the structural element selection can strongly influence the accuracy of the estimated corrosion damage effect.     

圆锥形钢管混凝土长柱力学性能研究

利用有限元分析软件ABAQUS建立圆锥形钢管混凝土长柱力学性能分析的三维实体有限元计算模型,并与相应的试验结果进行对比。结果表明:有限元计算与试验所得的荷载-3H/4挠度曲线、承载力及破坏形态吻合较好。在此基础上,对圆锥形钢管混凝土长柱受力全过程中钢管与混凝土应力、应变分布情况进行分析,同时给出钢管与混凝土之间的相互作用规律,并对长细比、锥度、偏心距、材料强度及钢管壁厚等参数对圆锥形钢管混凝土长柱初始刚度、承载力及荷载-3H/4挠度曲线的影响进行比较。结果表明:圆锥形钢管混凝土长柱在3H/4处发生侧向挠曲破坏,长细比、锥度、偏心距、混凝土抗压强度及钢管壁厚等参数对其力学性能影响显著,钢管屈服强度对其力学性能影响不明显。     

HRB600钢筋混凝土短柱轴压性能试验研究

通过对6根HRB600钢筋、1根HRB500钢筋混凝土短柱和2根素混凝土短柱进行轴心受压试验,分析不同配筋率、混凝土强度、钢筋强度、长细比对钢筋混凝土柱轴压性能的影响,提出HRB600钢筋的抗压强度设计值,分析GB 50010-2010《混凝土结构设计规范》中关于轴心受压承载力计算公式的适用性。研究结果表明:随着纵筋配筋率、钢筋强度和混凝土强度的提高,轴压短柱的峰值荷载增大;轴压短柱峰值应变随混凝土强度提高而减小,随钢筋强度提高而略有增大,纵筋配筋率和长细比对峰值应变影响较小;HRB600钢筋抗压强度设计值取为500 MPa,HRB600钢筋混凝土短柱与普通钢筋混凝土短柱的受力性能相似,轴心受压承载力可以按照GB 50010-2010《混凝土结构设计规范》中规定的受压承载力公式进行计算,具有足够的安全储备。     

带肋冷弯薄壁方钢管混凝土柱滞回性能研究

对3根带肋冷弯薄壁方钢管混凝土柱进行滞回试验,主要参数为轴压比。试验结果表明：纵向加劲肋有效延缓了钢管壁局部屈曲的发生;其滞回曲线饱满,具有良好的耗能能力;随着轴压比的增大,柱承载力略有增大,而延性、耗能能力则明显减小;当横向位移大于6倍的屈服位移时,大轴压比的刚度退化速度最快。建立了该类试件的有限元模型,对比可得有限元模拟结果与试验结果吻合较好。基于有限元模型对该类构件开展机理分析和参数分析。结果表明：在带肋冷弯薄壁方钢管的约束下,核心混凝土的强度得到了较大提高;钢管局部屈曲发生在峰值荷载后,局部屈曲只发生在纵向加劲肋和钢管角部间;材料强度、轴压比、钢管宽厚比和长细比等参数对该类构件的承载力有较大影响;混凝土强度、轴压比和长细比对荷载-位移骨架曲线形状有较大影响。基于参数分析建议了该类构件的简化滞回模型,简化计算结果和有限元计算结果吻合较好。     

An experimental behaviour of concrete-filled steel tubular columns

In this paper results of tests conducted on 27 concrete-filled steel tubular columns are reported. The test parameters were the column slenderness, the load eccentricity covering axially and eccentrically loaded columns with single or double curvature bending and the compressive strength of the concrete core. The test results demonstrate the influence of these parameters on the strength and behaviour of concrete-filled steel tubular columns. A comparison of experimental failure loads with the predicted failure loads in accordance with the method described in Eurocode 4 Part 1.1 showed good agreement for axially and eccentrically loaded columns with single curvature bending whereas for columns with double curvature bending the Eurocode loads were higher and on the unsafe side. More tests are needed for the case of double curvature bending.     

Empirical formulations for predicting the ultimate compressive strength of welded aluminum stiffened panels

The present study was undertaken by the support from Ship Structure Committee (http://www.shipstructure.org), a North American-based interagency research and development committee, in association with SR-1446 project, and also from Alcan Marine, France. Empirical expressions are developed for predicting the ultimate compressive strength of welded aluminum stiffened panels used for marine applications. Existing data of the ultimate compressive strength for aluminum stiffened panels experimentally and numerically obtained by the SR-1446 project is used for deriving the formulations which are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. The formulae implicitly include the effects of weld induced initial imperfections, and softening in the heat affected zone.     

Performance of steel H columns loaded under uniform temperature

This paper presents the experimental results for a series of H steel columns under fire load. The width-to-thickness ratio of steel plates and the slenderness ratios of steel columns are two dominating factors linked to local buckling and global buckling of columns, respectively. To evaluate the influence of these two factors on the structural behavior of steel columns in fire conditions, a series of H steel columns were loaded to their limit states at specified temperature levels. The steady state method has been adopted in order to derive the structural behavior of steel columns at specified temperatures directly.On the basis of the experimental results, it has been found that steel columns with non-compact section are able to reach yield strength at elevated temperature. That is, the width-to-thickness ratio, designed in accordance with current ambient temperature specifications, is capable of preventing brittle failure of steel columns in fire conditions. Depending on the slenderness ratio, the failure of steel columns may change from global buckling at ambient temperature to local buckling at elevated temperature. For plastic section columns with a slenderness ratio greater than 50, column strength drops dramatically to 40% of its strength at ambient temperature. At temperature levels of 500 ^°C, the column retains more than 70% of its ambient temperature strength if the slenderness ratio of the column is less than 50. However, in the case of temperature levels exceeding 500 ^°C, or when the slenderness ratio is greater than 50, column strength drops significantly. On the basis of this study, it is tentatively suggested that 500 ^°C be adopted as the critical temperature for steel members subjected to compression in order to ensure that the column strength keeps higher than 2/3 of the ambient temperature yield strength. The slenderness ratio of steel columns should be limited to 50, so as to prevent brittle failure of steel columns under fire attack.     

Calculation of slenderness ratio for laced columns with serpentine and crosswise lattices

In contrast to the technique accepted in existing design specifications, a slenderness ratio for laced columns with serpentine or crosswise lattices is determined as a result of consideration of the laced column as a statically indeterminate structure. Recent results of solving the buckling problem for laced columns, on the one hand, and the well known relationship between the slenderness ratio of the compressed bar and its elastic critical force, on the other hand, enable representation of the slenderness ratio of the laced column as a function of the special lattice rigidity parameter and the number panels into which the lattice joints divide the column chords. The obtained curves of the slenderness ratio for columns with a different number of panels are slightly distinguished one from another. As a consequence the single dependence between the modified slenderness ratio of the column and the lattice rigidity parameter can be accepted for columns regardless of the number of panels. This dependence is constructed by enveloping at the top the curves corresponding to fixed numbers of panels. The obtained plots of the modified slenderness ratio for columns with serpentine and crosswise lattices can be applied in designing steel-laced columns.     

毛竹压杆屈曲系数公式研究

为获得四川地区毛竹压杆更精确的屈曲系数公式，通过试验方法测定四川地区毛竹的顺纹抗压强度以及31根长细比分布较为均匀的竹压杆临界荷载，并对国内外现有的9个竹压杆屈曲系数公式进行研究。结果表明：此批毛竹顺纹抗压强度平均值约为51MPa；竹压杆的破坏是由于局部鼓曲变形和整体弯曲变形叠加，最终竹压杆管壁超过横纹抗拉强度极限值进而纵向开裂；现有竹压杆屈曲系数公式所得到的临界荷载计算值之间有所差异，与文中试验实测临界荷载值也有不同程度的差异。最后采用具有较好拟合优度的Ylinen方法，基于文中试验数据拟合提出适用于四川地区的毛竹压杆屈曲系数公式。     

长细比对螺旋箍筋柱轴心受压承载力的影响

在GB 50010—2010《混凝土结构设计规范》中,螺旋箍筋柱轴心受压承载力计算公式未能定量反映长细比的影响,与普通箍筋柱计算公式及国内外其他有关规范公式的差异较大。为了定量分析长细比对螺旋箍筋柱轴心受压性能的影响,基于ANSYS软件建立了钢筋混凝土螺旋箍筋柱的精细化弹塑性有限元模型,采用经过验证的有限元模型开展了不同直径和长径比的螺旋箍筋柱轴心受压加载破坏过程的有限元分析。结果表明：螺旋箍筋柱的承载力随着核心区长径比的增大而逐渐降低,当长径比由2增大至5时,其承载力降低幅度在3.7%以内;当长径比达到15时,其承载力较长径比为2时相应值降低了25%。在计算分析的基础上,提出了螺旋箍筋柱轴心受压承载力计算公式中稳定系数的取值建议。     

圆形钢管混凝土柱抗压强度

通过对24个钢管混凝土柱(CFST)施加轴向压力直到破坏的试验,以研究其性能。试验中考虑的变量包括钢管的长度、直径、强度和混凝土的强度。由于长细比较大,造成系列1中的所有组合柱发生整体弯曲屈曲而破坏。尽管系列2试验中的组合柱也经历了整体弯曲屈曲,但"短柱"的破坏是由混凝土压碎和钢管失效引起的。将试验结果与采用南非规范(SANS10162-1)和欧洲规范(EC4)计算得到的荷载值进行对比表明,2种规范结果均偏保守,对系列1试验,分别达到8.4%和13.6%,对系列2试验,分别达到10.5%和20.2%。压力与竖向变形曲线显示受压柱具有很好的延性。     

钢管混凝土短柱的基本性能和强度计算

本文报导了57个钢管混凝土轴心受压短柱(L/D≤4)的试验结果。试验的主要参数为套箍指标、加载方式和试件高度。试验表明,加载方式和试件高度对短柱承载能力的影响不明显。 文中探讨了钢管混凝土轴压短柱的工作机理。用教授的极限平衡法推导了短柱极限强度的计算公式。基本假设为:1.核心混凝土处于三向受压应力状态,钢管处于纵压-环拉的双向应力状态;2.三向受压下混凝土的强度条件可用经验公式(3)描述;3.钢管服从Von Mises屈服条件。经用本文的和文献上的试验结果对建议公式进行校核,实测值与计算值符合良好。     

椭圆形钢管混凝土长柱偏压力学性能研究

利用有限元分析软件ABAQUS建立了椭圆形钢管混凝土长柱偏压力学性能分析的有限元模型,并对12个椭圆形钢管混凝土长柱的偏压试验结果与有限元模拟结果进行对比。结果表明:有限元计算与试验所得的荷载-挠度全过程曲线、承载力及破坏形态吻合较好。在此基础上对其受力过程中钢管及混凝土应力、应变分布情况进行分析,同时给出钢管与混凝土之间的相互作用,并对长细比、偏心距、材料强度、钢管壁厚等参数对长柱偏压极限承载力及荷载-柱中挠度曲线的影响进行比较。结果表明:椭圆形钢管混凝土长柱在H/2处发生侧向挠曲破坏,长细比、混凝土抗压强度、钢管壁厚及偏心距等参数对其力学性能影响显著,钢管屈服强度对其力学性能影响不明显。     

Structural response of stainless steel oval hollow section compression members

Cold-formed stainless steel oval hollow sections (OHS) offer the combined aesthetic appeal of circular hollow sections and stainless steel, together with the structural efficiency associated with cross-sections of differing geometric properties about their two principal axes. To date, no structural design guidance exists for these cross-sections, principally due to their relatively recent introduction and a lack of fundamental structural test data. This paper examines the structural response of stainless steel OHS compression members and presents design recommendations. A series of laboratory tests was carried out to generate fundamental structural performance data. Tensile coupon tests were initially performed to establish the basic material stress–strain characteristics of the sections. These were followed by stub column tests to determine the average compressive response of the cross-sections and flexural buckling tests to obtain ultimate load carrying capacity data for use in the determination of a suitable buckling curve for stainless steel OHS. Measurements of the geometric properties of the test specimens including initial imperfections were carried out. The full load–displacement responses of the specimens were recorded and have been presented herein. A finite element (FE) modelling programme was performed in parallel with the experimental study. Once the FE models had been validated against the test results, parametric studies were carried out to further investigate the influence of individual key parameters, including the aspect ratio and local slenderness of the cross-sections as well as the member slenderness. Based on the obtained experimental and numerical results, a class 3 limit for stainless steel OHS in compression and a suitable buckling curve for OHS columns have been proposed.     

钢管钢纤维混凝土圆柱的试验研究

进行了钢管钢纤维混凝土圆柱的性能研究。制作了16根钢管混凝土柱,并进行了双向压弯试验。主要参数有:横截面尺寸、柱长、混凝土抗压强度、荷载偏心。考虑材料非线性和几何非线性,提出计算钢管混凝土柱的极限承载力和荷载-位移曲线的理论方法,将普通钢管混凝土柱和钢管钢纤维混凝土柱的极限承载力和荷载-位移曲线的试验数据与理论分析进行对比。结果表明,钢纤维对钢管混凝土的性能有很大影响。     

Experimental tests of slender reinforced concrete columns under combined axial load and lateral force

The use of high strength concrete (HSC) in columns has become more frequent since a substantial reduction of the cross-section is obtained, meaning that slenderness increases for the same axial load and length, producing higher second order effects. However, the experimental tests in the literature of reinforced concrete columns subjected to axial load and lateral force focus on shear span ratios, according to Eurocode 2 (2004), clause 5.6.3., (M/(V⋅h)) lower than 6.5. This gap in the literature limits technological development for the construction of these structural elements. This paper presents 44 experimental tests on reinforced concrete columns subjected to constant axial load and monotonic lateral force. The aim of this is to gain greater knowledge of the types of elements which will also be of use in calibrating the numerical models and validating the simplified methods. The test parameters are strength of concrete (normal- and high-strength concrete), shear span ratio, axial load level and longitudinal and transversal reinforcement ratios. The strength and deformation of the columns were studied, and an analysis of the simplified methods from Eurocode 2 (2004) and ACI-318 (2008) concluded that both are very conservative.     

圆端形椭圆钢管混凝土长柱偏压受力性能研究

为了获悉圆端形椭圆钢管混凝土偏压长柱的理论计算模型和受力性能,考虑了圆端形椭圆截面特征,提出了圆端形椭圆钢管混凝土本构关系等效方法;基于有限元法建立了圆端形椭圆钢管混凝土长柱在偏压作用下的理论分析模型。对钢材强度、混凝土强度、偏心距、径厚比、长短轴比和长细比等诸多参数进行了系统分析,评价了各参数对圆端形椭圆钢管混凝土长柱偏压承载力的影响,揭示了其破坏模式。研究结果表明:圆端形椭圆钢管混凝土偏压长柱的承载力随着混凝土强度和钢材强度的增大而增大;随着偏心率、径厚比、长短轴比和长细比的增大而减小。最后,基于统一理论提出了圆端形椭圆钢管混凝土长柱偏压作用下的承载力设计方法。研究结果将为建立圆端形椭圆钢管混凝土结构的设计和应用提供参考。     

Seismic behaviour of square CFT beam-columns under biaxial bending moment

This paper investigates the behaviour of square concrete-filled steel tubular (CFT) beam-columns subjected to biaxial moment. Nine tests on beam-columns are reported here under a combined loading of constant axial load and cyclic lateral load applied at varying angles to the axis of the cross-section, referred to as ‘diagonal’ loading. The specimens were prepared in order to evaluate the influence of different parameters on the overall structural response, their ductility and their energy dissipation ability; the parameters included the effects of axial load ratio, width-to-thickness ratio, concrete compressive strength, slenderness ratio and load angle on the moment strength. The experimental results indicate that the ductility and energy dissipation ability of biaxially loaded square CFT columns decrease with increasing the axial load ratio. Their ductility and energy dissipation ability was also observed to decrease as the concrete compressive strength increased while the ductility was barely affected by the load angle. An increase in the load angle of biaxially bent square CFT beam-columns led to a slight decrease of the moment strength. Both EC4 and AIJ code provisions were shown to predict with reasonable accuracy the moment strength capacity observed in the tests, while the ACI-predicted moment strength gave to slightly conservative values. On the other hand, the LRFD code provisions greatly underestimated their moment strength.