Effect of chord configuration and spacing on cyclic flexural response of built-up columns

As per the current codes of practice, the design of battens of a built-up steel column depends on the level of axial load. These columns may not reach their plastic moment capacities under the lateral loading due to the premature instability of main chords in the expected plastic hinge regions. In this study, the cyclic performance of built-up battened columns is analytically evaluated under the gradually-increasing lateral displacements and the constant axial loads using a finite element software ABAQUS. The main parameters varied are the chord spacing, the column slenderness ratio, the level of axial load, and the chord configuration. Ninety-eight FE models of battened columns are analysed in this study in which the hot-rolled steel channel or I-Sections are used as the main chords. The analytical results showed that the built-up columns made up from I-sections have better lateral strength and ductility as compared to the Channel sections for nearly same values of axial load and slenderness ratio. Based on the analytical results, the limiting values of chord spacing, slenderness ratio and level of axial loads are proposed in order to delay the effect of instability on their lateral load resistance. Further, the interaction between axial load-moment capacity of built-up columns is discussed for various types of chord configurations.     

往复荷载作用下矩形钢管混凝土构件力学性能的研究

以往 ,国内外学者对矩形钢管混凝土构件滞回性能的研究尚少见报道。本文以矩形钢管混凝土构件截面高宽比和轴压比为主要参数 ,进行了 3 0个构件滞回性能的实验研究。利用数值方法分析了矩形钢管混凝土构件的滞回性能 ,理论计算结果与实验结果吻合较好。利用数值方法 ,系统分析和考察了轴压比、长细比、含钢率、截面高宽比、钢材屈服强度和混凝土强度等参数对滞回曲线骨架线的影响规律 ,在此基础上 ,提出了矩形钢管混凝土构件弯矩 -曲率和P -Δ滞回关系模型 ,以及位移延性系数的简化计算方法。     

双槽钢缀板柱绕虚轴的滞回性能试验研究

为研究双槽钢缀板柱绕虚轴的抗震性能,对6个双槽钢缀板柱足尺试件进行水平往复荷载试验研究,分析了单肢长细比、缀板线刚度、轴压比、加劲肋设置等因素对试件的承载力、破坏模式、耗能能力、变形能力及延性的影响。试验结果表明：按GB 50017—2017《钢结构设计标准》设计的双槽钢缀板柱在绕虚轴往复荷载作用下不能达到设计塑性受弯承载力,减小单肢长细比,可显著提高构件塑性抗弯承载力及初始刚度,当单肢长细比为20时,构件绕虚轴受弯承载力可达到规范相关要求;在满足规范要求的情况下,缀板及其连接焊缝未发生破坏,但提高缀板线刚度对构件绕虚轴的抗震性能影响较小;轴压比对构件抗震性能影响显著,随着轴压比增大,构件抗震性能降低;在构件塑性铰区设置加劲肋,可有效防止该区域板件的局部屈曲,提高构件的承载力、延性及耗能能力,缓解承载力及刚度退化,但塑性铰区转移至第二与第三块缀板间,试件破坏模式为单肢失稳。     

Cyclic performance of concrete-filled steel CHS columns under flexural loading

Concrete-filled steel CHS (circular hollow section) columns are currently being increasingly used in the construction of buildings. Limited information is available on the models for the moment (M) versus curvature (?) response, and the lateral load (P) versus lateral displacement (Δ) relationship of these columns subjected to axial load and cyclically increasing flexural loading.Eight concrete-filled steel CHS specimens were tested under constant axial load and cyclically increasing flexural loading. The parameters in the study included the concrete strength (f_cu) and the axial load level (n). A mechanics model is developed in this paper for concrete-filled steel CHS columns subjected to constant axial load and cyclically increasing flexural loading. The predicted cyclic responses for the composite columns are in good agreement with test results.Based on the theoretical model, parametric analysis was performed on the behaviours of the moment (M) versus curvature (?) response, and the lateral load (P) versus lateral displacement (Δ) relationship, as well as the ductility coefficient (μ) for the composite columns. Finally, simplified models for the moment (M) versus curvature (?) response, and the lateral load (P) versus lateral displacement (Δ) relationship are suggested. A formula for the calculation of the ductility coefficient (μ) of the composite columns under constant axial load and cyclically increasing flexural loading is developed.     

Seismic behavior and moment strength of tubed steel reinforced-concrete (SRC) beam-columns

The seismic behavior of tubed SRC beam-columns has been investigated by testing six specimens subjected to combined constant axial compression and lateral cyclic load. Two circular tubed SRC columns (CTSRC) and two square tubed SRC (STSRC) columns as well as two common SRC columns as comparison were tested in this paper. Different axial load ratio (n₀ = 0.3 and 0.5) have been adopted for the constant axial load. The test results indicated that the flexural strength of a CTSRC column was much higher than that of a common SRC column with the same steel ratio and axial compressive load, whereas there was little difference on the flexural strength of a STSRC columns and a common SRC column. The ductility, plastic deformation capacity and energy dissipation capacity of CTSRC and STSRC columns were much higher than those of common SRC columns with the same steel ratio and axial compressive load. The flexural strength increased as the axial load ratio increased for CTSRC and STSRC columns, while an opposite trend was observed for the plastic deformation capacity. The flexural strength and plastic deformation capacity of CTSRC columns were clearly higher than that of the STSRC beam-columns with the same steel ratio and axial load ratio. A modified EC4 code method has been proposed for the calculation of the moment strength for tubed SRC columns.     

角钢约束混凝土轴压短柱力学性能研究

对10个高宽比为3的角钢约束混凝土短柱进行轴心受压试验,观察试件的破坏过程,得到了试件的荷载 轴向位移关系曲线,根据试验结果,分析了构件截面尺寸、缀板间距以及混凝土强度对角钢约束混凝土柱承载力的影响;利用有限元软件ANSYS对试验过程进行数值仿真分析。结果表明：试件最终破坏时在试件中部附近位置角钢和缀板出现凸鼓变形;随着缀板间距的增大,试件的承载力逐渐减小,荷载 位移曲线下降越明显,可见在相同条件下,缀板间距是影响角钢约束混凝土短柱承载力的主要因素。在试验和仿真分析的基础上提出角钢约束混凝土轴压短柱承载力的简化计算式。     

螺旋筋约束增强空腹式型钢混凝土柱滞回性能试验研究

为了研究螺旋筋约束增强空腹式型钢混凝土柱的滞回性能,以轴压比、配箍率、配钢形式以及截面形式为变化参数,设计10个试件（其中空腹式型钢混凝土柱对比试件1个,复合螺旋箍筋混凝土柱对比试件1个）进行低周反复加载试验。观察试件的破坏形态,获取各试件的滞回曲线和骨架曲线。分析试件的极限承载力、层间位移角、延性、耗能、强度衰减和刚度退化等抗震性能指标,以及各变化参数对其抗震性能的影响。结果表明：螺旋筋约束增强空腹式型钢混凝土柱主要表现为弯曲破坏和黏结破坏;相比空腹式型钢混凝土柱和复合螺旋箍筋混凝土柱,螺旋筋约束增强空腹式型钢混凝土柱的滞回曲线更为饱满,承载力、延性和耗能均有提高;随着轴压比的增大,其承载力、刚度和耗能能力提高,但延性和变形能力降低,强度衰减和刚度退化现象更为严重;随着螺旋箍筋配箍率的增大,承载力、刚度、延性、耗能能力和变形能力逐渐提高;相同总含钢量下,增大螺旋筋配箍率比增大型钢间接配钢率对其延性和耗能能力的提高更显著,对其承载力则相反;三种截面形式中,Ⅲ类截面试件表现出最优的抗震性能。     

曲线形钢管混凝土(CCFST)组合构件轴压试验

描述了一系列曲线形钢管混凝土(CCFST)组合构件的轴压试验。对20个试件(其中包含18个CCFST组合构件和2个曲线形中空截面钢管柱)进行了试验,研究组合构件中管件形状(圆形和方形)、初始曲率(βr,0%～7.4%)、名义长细比(λn,9.9～18.9)、截面形式(2种主要构件、3种主要构件和4种主要构件)以及支撑形式(板条和绳状)等因素对其性能的影响。试验结果表明:CCFST组合构件试样的极限强度和刚度随着βr或λn的增加而降低。板条和绳状支撑组合构件的承载力和失效模式不同。给出利用等效长细比计算轴压下CCFST组合构件极限强度的简单方法。     

高轴压比钢管混凝土剪力墙抗震性能试验研究

为研究约束边缘构件内配置圆钢管的钢管混凝土剪力墙的抗震性能、探讨钢管混凝土剪力墙的轴压比限值及其约束边缘构件的配箍要求,完成了6个剪跨比大于2.0的高轴压比钢管混凝土剪力墙试件和1个钢筋混凝土剪力墙试件的拟静力试验。试验结果表明：剪力墙的破坏形态为压弯破坏及底部混凝土压溃而丧失竖向承载能力;钢管混凝土剪力墙的开裂水平力、名义屈服水平力、正截面受弯承载力和变形能力均比相同参数的钢筋混凝土剪力墙大;配置双钢管剪力墙的变形能力大于配置单钢管的剪力墙,约束边缘构件为端柱的剪力墙的变形能力大于约束边缘构件为暗柱的剪力墙;正截面受弯承载力试验值大于计算值。根据试验结果,提出了钢管混凝土剪力墙的设计建议。图9表7参13     

Elastic lateral buckling of cantilever Litesteel Beams under transverse loading

The LiteSteel Beam (LSB) is a new hollow flange channel section developed by OneSteel Australian Tube Mills using its patented dual electric resistance welding and automated continuous roll-forming technologies. The LSB has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. Its flexural strength for intermediate spans is governed by lateral distortional buckling characterised by simultaneous lateral deflection, twist and web distortion. Recent research on LSBs has mainly focussed on their lateral distortional buckling behaviour under uniform moment conditions. However, in practice, LSB flexural members are subjected to non-uniform moment distributions and load height effects as they are often under transverse loads applied above or below their shear centre. These loading conditions are known to have significant effects on the lateral buckling strength of beams. Many steel design codes have adopted equivalent uniform moment distribution and load height factors based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. The non-uniform moment distribution and load height effects of transverse loading on cantilever LSBs, and the suitability of the current design modification factors to include such effects are not known. This paper presents a numerical study based on finite element analyses of the elastic lateral buckling strength of cantilever LSBs subject to transverse loading, and the results. The applicability of the design modification factors from various steel design codes was reviewed, and suitable recommendations are presented for cantilever LSBs subject to transverse loading.     

中等剪跨比RC剪力墙拉-弯-剪受力性能试验研究

为研究中等剪跨比钢筋混凝土(RC)剪力墙的拉-弯-剪受力性能，对4个RC剪力墙开展了在恒定轴拉力和往复水平力作用下的拟静力试验。RC墙剪跨比为1.5，尺寸和配筋均相同，仅轴拉力变化。结果表明：RC墙分别发生了剪切破坏、弯曲-剪切破坏和弯曲破坏；轴拉力致使RC墙的水平承载力降低，竖向钢筋平均拉应力比ns从0.20增大到0.80时，RC墙峰值荷载降低了约55%；中等剪跨比RC墙弯曲-剪切耦合效应明显，墙底部截面弯曲屈服后，塑性铰区的剪切变形也表现出显著的非线性；轴拉力和往复水平力作用下墙体发生显著的轴向伸长，引起墙体受剪承载力退化，竖向钢筋平均拉应力比ns=0.40的RC墙，其受力由弯曲机制向剪切机制转变，出现了弯曲-剪切破坏，基于转动角软化桁架模型和轴向伸长的实测数据，定量计算了该类墙体的受剪承载力退化，揭示了弯曲-剪切破坏机理。最后，验证了美国ACI 318—14和中国JGJ 3—2010中RC墙正截面拉弯承载力计算方法和公式的适用性。     

中等剪跨比RC剪力墙拉-弯-剪受力性能试验研究

为研究中等剪跨比钢筋混凝土(RC)剪力墙的拉-弯-剪受力性能,对4个RC剪力墙开展了在恒定轴拉力和往复水平力作用下的拟静力试验。RC墙剪跨比为1.5,尺寸和配筋均相同,仅轴拉力变化。结果表明：RC墙分别发生了剪切破坏、弯曲-剪切破坏和弯曲破坏;轴拉力致使RC墙的水平承载力降低,竖向钢筋平均拉应力比ns从0.20增大到0.80时,RC墙峰值荷载降低了约55%;中等剪跨比RC墙弯曲-剪切耦合效应明显,墙底部截面弯曲屈服后,塑性铰区的剪切变形也表现出显著的非线性;轴拉力和往复水平力作用下墙体发生显著的轴向伸长,引起墙体受剪承载力退化,竖向钢筋平均拉应力比ns=0.40的RC墙,其受力由弯曲机制向剪切机制转变,出现了弯曲-剪切破坏,基于转动角软化桁架模型和轴向伸长的实测数据,定量计算了该类墙体的受剪承载力退化,揭示了弯曲-剪切破坏机理。最后,验证了美国ACI 318—14和中国JGJ 3—2010中RC墙正截面拉弯承载力计算方法和公式的适用性。     

夹层钢管混凝土梁-柱在循环荷载作用下的性能分析

夹层钢管混凝土(CFDST)在桥梁和建筑的建设中具有很大的潜能。轴力和循环加载的弯曲荷载作用下,弯矩曲率曲线(M-(?)),柱侧向荷载-侧移曲线(P-Δ)模型的研究信息非常有限。建立了一个力学模型,用于分析轴向恒荷载和循环加载的弯曲荷载作用下的CFDST梁-柱。预测的组合梁柱的循环反应性能与试验结果一致。基于这个理论模型,对组合梁柱有关弯矩曲率曲线(M-(?)),侧向荷载-侧移曲线(P-Δ)的性能进行了参数分析。最后,提出了计算弯矩曲率曲线(M-(?)),侧向荷载-侧移曲线(P-Δ)的简化模型。     

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.     

Reinforced concrete columns strengthened with angles and battens subjected to eccentric load

The aim of the work is, on the one hand, the presentation of a theoretical fiber model able to predict the moment–curvature behaviour of RC columns confined by means of angles and battens and, on the other hand, the validation of the proposed model by means of the comparison between analytical results and experimental evidence coming from 13 specimens tested under axial force–moment interaction.The analytical model is able to account for many parameters often neglected in current design practice, such as the influence of both hoops and battens on concrete confinement, the buckling of longitudinal bars and the influence of the structural detail aimed at assuring the continuity through the concrete floor slab which affects the angle behaviour. The proposed model has been used for predicting the load carrying capacity of both unstrengthened and strengthened columns, obtaining a good degree of accuracy. In addition, the comparison in terms of moment–rotation curves has been performed, showing the model accuracy in predicting the structural response in the whole deformation range.     

Curved concrete filled steel tubular (CCFST) built-up members under axial compression: Experiments

A series of tests on curved concrete filled steel tubular (CCFST) built-up members subjected to axial compression is described in this paper. Twenty specimens, including 18 CCFST built-up members and 2 curved hollow tubular built-up columns, were tested to investigate the influence of variations in the tube shape (circular and square), initial curvature ratio (β_r, from 0 to 7.4%), nominal slenderness ratio (λ_n, from 9.9 to 18.9), section pattern (two main components, three main components and four main components), as well as brace pattern (battened and laced) on the performance of such composite built-up members. The experimental results showed that the ultimate strength and stiffness of CCFST built-up specimens decreased with increasing β_r or λ_n. Different load-bearing capacities and failure modes were obtained for the battened and laced built-up members. A simplified method using an equivalent slenderness ratio was suggested to calculate the strength of CCFST built-up members under axial compression.     

A simplified method for flexural capacity assessment of circular RC cross-sections

A simplified method for the assessment of bending moment resistance for reinforced concrete (RC) members with circular cross-sections is presented. In the proposed method longitudinal rebars arrangement is replaced with a thin steel ring equivalent to the steel total area; moreover, according to modern codes, simplified stress-strain relationships for concrete and reinforcing steel are used.The performed analyses demonstrate that the value of flexural capacity determined by the proposed approach, is very close to the results obtained by applying rigorous methods based on analytical and numerical algorithms.The study also proves that in members subjected to bending moment without axial load, the flexural strength depends on the geometry of the section (i.e. radius and concrete cover) and on mechanical ratio of steel reinforcement by a very simple formula.     

Numerical modelling and design of LiteSteel Beams subject to lateral buckling

The LiteSteel Beam (LSB) is a new hollow flange channel section developed using a patented dual electric resistance welding and cold-forming process. It has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a slender web, and is commonly used as flexural members. However, the LSB flexural members are subjected to a relatively new lateral distortional buckling mode, which reduces their moment capacities. Unlike lateral torsional buckling, the lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist and cross sectional change due to web distortion. Therefore a detailed investigation into the lateral buckling behaviour of LSB flexural members was undertaken using experiments and finite element analyses. This paper presents the details of suitable finite element models developed to simulate the behaviour and capacity of LSB flexural members subject to lateral buckling. The models included all significant effects that influence the ultimate moment capacities of such members, including material inelasticity, lateral distortional buckling deformations, web distortion, residual stresses, and geometric imperfections. Comparison of elastic buckling and ultimate moment capacity results with predictions from other numerical analyses and available buckling moment equations, and experimental results showed that the developed finite element models accurately predict the behaviour and moment capacities of LSBs. The validated model was then used in a detailed parametric study that produced accurate moment capacity data for all the LSB sections and improved design rules for LSB flexural members subject to lateral distortional buckling.     

钢管约束钢筋混凝土压弯构件滞回性能试验研究与分析

进行了4个圆钢管约束钢筋混凝土(CTRC)和4个方钢管约束钢筋混凝土(STRC)压弯构件滞回性能的试验研究,并进行了两个钢筋混凝土(RC)对比试件的试验研究。试验中的主要参数为轴压比(0.34、0.65和0.80)和混凝土强度等级(C30和C60)。试验结果表明,由于钢管对核心混凝土的有效约束,核心高强混凝土柱的承载力、延性和耗能能力得到了显著提高。随轴压比和混凝土强度的提高,CTRC压弯构件的受弯承载力提高;但轴压比和混凝土强度对试件的延性无明显影响。随轴压比和混凝土强度的提高,STRC压弯构件的受弯承载力提高,但延性下降。相同轴压比条件下,CTRC压弯构件的受弯承载力和延性明显优于STRC构件。根据试验结果,建议了钢管约束钢筋混凝土柱截面受弯承载力的计算方法。建立了钢管约束钢筋混凝土压弯构件的纤维模型数值计算方法,计算中采用随荷载的增加而不断增大钢管对核心混凝土的约束效应的方法,数值计算结果与试验结果吻合良好。     

Analytical behaviour of concrete-filled double skin steel tubular (CFDST) beam-columns under cyclic loading

Concrete-filled double skin steel tubes (CFDST) have a great potential to be used in the construction of bridges and buildings. Limited information is available on the models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (Δ) relationship of these columns subjected to axial load and cyclically increasing flexural loading. A mechanics model is developed in this paper for CFDST beam-columns subjected to constant axial load and cyclically increasing flexural loading. The predicted cyclic responses for the composite columns are in good agreement with test results. Based on the theoretical model, parametric analysis was performed on the behaviours of moment (M) versus curvature (φ) response and lateral load (P) versus lateral displacement (Δ) relationship for the composite columns. Finally, simplified models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (Δ) relationship were suggested.