Seismic performance of recycled concrete-filled square steel tube columns

An experimental study on the seismic performance of recycled concrete-filled square steel tube （RCFST） columns is carried out. Six specimens were designed and tested under constant axial compression and cyclic lateral loading. Two parameters, replacement percentage of recycled coarse aggregate （RCA） and axial compression level, were considered in the test. Based on the experimental data, the hysteretic loops, skeleton curves, ductility, energy dissipation capacity and stiffness degradation of RCFST columns were analyzed. The test results indicate that the failure modes of RCFST columns are the local buckling of the steel tube at the bottom of the columns, and the hysteretic loops are full and their shapes are similar to normal CFST columns. Furthermore, the ductility coefficient of all specimens are close to 3.0, and the equivalent viscous damping coefficient corresponding to the ultimate lateral load ranges from 0.323 to 0.360, which demonstrates that RCFST columns exhibit remarkable seismic performance.

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.

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.

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.

Low cyclic fatigue performance of concrete-filled steel tube columns

Eight concrete-filled steel tubular(CFT) columns were tested subjected to cyclic loading under constant axial load. Experimental parameters included axial compression ratio, loading sequences, and strength of concrete and steel. The seismic performance of CFT columns and failure modes were analyzed. The test results show that different axial load ratios and loading sequences have effects on the load carrying capacity, ductility and energy dissipation capacity of CFT columns, as well as the failure modes of the CFT columns. The failure pattern can be categorized into two types: local buckling failure of steel tube in compression zone, and low cycle fatigue tearing rupture failure of steel tube. The seismic behavior was evaluated through the energy index obtained from each cycle.

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

Behavior of High Strength Concrete Filled Square Steel Tube Stub Columns with Inner CFRP Tube Under Biaxial Eccentric Compression

This paper studies the contribution of CFRP(carbon fiber-reinforced polymer)to the mechanical behavior of high strength concrete-filled square steel tube(HCFST)under biaxial eccentric compression.The new type of composite member is composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes.The finite element analysis was made by ABAQUS on the behavior of high strength concrete filled square steel tubular columns with inner CFRP circular tube subjected to bi-axial eccentric loading.The results obtained from the finite element analysis were verified with the experimental results.In addition,the load-deflection curves in the whole process were calculated and analyzed,which can be divided into three segments:Elastic phase,plastic phase,descending phase.Based on the load-deflection curves,the stresses analysis on the core concrete,CFRP tube and steel tube were conducted.The confinement effect of the CFRP tube improves the ductility of HCFST-CFRP stub column.CFRP ratio and eccentricity affect the ultimate bearing capacity of HCFST stub column.Finally,a calculation formula of ultimate bearing capacity was proposed in the paper.

Prediction of Axial Capacity of Concrete-Filled Square Steel Tubes Using Neural Networks

The application of artificial neural network to predict the ultimate bearing capacity of CFST （ concrete-filled square steel tubes） short columns under axial loading is explored. Input parameters consiste of concrete compressive strength, yield strength of steel tube, confinement index, sectional dimension and width-to-thickness ratio. The ultimate bearing capacity is the only output parameter. A multilayer feedforward neural network is used to describe the nonlinear relationships between the input and output variables. Fifty-five experimental data of CFST short columns under axial loading are used to train and test the neural network. A comparison between the neural network model and three parameter models shows that the neural network model possesses good accuracy and could be a practical method for predicting the ultimate strength of axially loaded CFST short columns.

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.

内置工字型CFRP型材高强圆钢管高强混凝土轴压短柱组合效应分析

目的 研究内置工字型CFRP型材的高强圆钢管高强混凝土短柱在轴心压力作用下三种材料的组合效应。方法 采用有限元分析软件ABAQUS对其进行数值模拟,通过相关试验验证模型的准确性,并对典型构件的破坏形态、受力全过程曲线进行分析,揭示构件各组成部分之间的相互作用和工作机理,评估CFRP配置率、钢材屈服强度、混凝土抗压强度、约束效应系数对组合效应的影响。结果 在高强圆钢管高强混凝土柱中内置CFRP型材,对构件的延性及安全裕度有显著提高,并改善了高强圆钢管对高强混凝土的约束,提高了构件的组合效应。结论 CFRP配置率控制在5.9%~8.4%,约束效应系数在1.2~1.4,钢材屈服强度不大于770 MPa时,构件中三种材料组合效应最佳。

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。

方形耐候钢管混凝土短柱轴压力学性能研究

为研究方形耐候钢管混凝土短柱的轴压力学性能,首先设计并开展了4根轴压短柱试验研究。进而采用Abaqus有限元软件建立方形耐候钢管混凝土短柱有限元模型并进行数值分析。数值模拟结果表明,轴压短柱直至破坏共经历了3个阶段:弹性段、弹塑性段和破坏段。其破坏模式均为柱中局部屈曲。耐候钢拉伸性能试验特征与低碳钢的力学性能相近,有限元建模采用低碳钢本构关系可准确模拟方形耐候钢管混凝土短柱的轴压力学性能。钢管内焊接拉筋能有效改善钢管对核心混凝土的约束作用,进而提高轴压短柱的极限承载力和延性。最后,方形耐候钢管混凝土短柱轴压力学性能与普通钢管混凝土短柱无异。

火灾下双钢管混凝土复合短柱的性能与承载力计算方法

为研究双钢管混凝土复合短柱的耐火性能,建立了双钢管混凝土复合短柱精细化数值模型,在类似构件试验成果验证的基础上,开展其高温反应规律和耐火性能影响因素研究;全面分析了内管径厚比、外管径厚比、内外管直径比等参数的影响,以及不同截面组合形式(内圆外圆、内方外圆和内圆外方)双钢管混凝土短柱的耐火极限。基于热传导分析理论推导双钢管混凝土短柱截面的温度场分布公式,并根据有限元模拟结果对公式进行修正;最后基于温度等效原理进一步提出了火灾条件下双钢管混凝土短柱截面温度场的简化计算公式和承载力计算方法。结果表明:双钢管混凝土复合短柱具有较好的耐火性能,在直径不变时增大内钢管的厚度以及在厚度不变时增加内钢管的直径都有利于耐火极限的提高;在荷载作用和含钢率相同的条件下,不同截面组合形式的双钢管混凝土短柱耐火极限相差不大,但总体上双圆钢管混凝土短柱的耐火性能偏优;提出的温度场简化计算公式和基于等效温度的承载力计算方法与有限元结果相对误差都在15%以内。

钢管再生混合短柱的轴压性能试验

为揭示钢管再生混合短柱的轴压性能,通过17根试件的轴压试验,考察钢管再生混合短柱与钢管混凝土短柱的7d和28d轴向受力行为,比较二者的刚度、强度和延性。根据国内外钢管混凝土结构设计标准,对试件的抗压承载力进行计算,基于计算结果与试验结果的对比,建议钢管再生混合短柱的抗压承载力计算公式。研究结果表明:①虽然钢管再生混合短柱采用了32%～35%的废弃混凝土,但其轴向受力性能却与全现浇钢管混凝土短柱相当。②根据我国标准JCJ01—89给出的钢管再生混合短柱的抗压承载力计算结果与试验结果吻合较好。

带约束拉杆T形钢管混凝土短柱轴压性能的试验研究

介绍11个带约束拉杆和5个不带约束拉杆的T形钢管混凝土轴压短柱试件的试验研究,讨论在不同约束拉杆间距与直径、钢板厚度与屈服强度、截面尺寸下带约束拉杆T形钢管混凝土短柱的破坏特点、承载力、拉杆与钢管的应变特点等轴压性能。结果表明:约束拉杆的设置改变了钢管的屈曲模态,延迟钢管局部屈曲的发生,有助于T形钢管混凝土轴压短柱的承载力和延性的提高。采用现有规范或规程的计算公式对试件轴压承载力进行计算,对不同计算方法的适用性进行探讨。

高强冷弯薄壁型钢轴压短柱受力性能试验研究

为了验证壁厚小于1 mm的G550级高强钢材对中国<冷弯薄壁型钢结构技术规范>(GB50018-2002)相关设计规定的适应性,进行了30根冷弯薄壁型钢方管截面轴压短柱的试验研究,试件的壁厚均为0.6 mm、宽厚比为20～150.试验结果表明:当宽厚比较小时(b/t≤40),试件的初始缺陷和高强钢材本身特性对构件承载力的影响较大,试件材料的强度得不到充分发挥;当宽厚比较大时(b/t＞40),高强钢材局部屈曲和有效截面是影响构件承载力的主要因素.通过对试验结果和各国规范计算结果的对比分析,给出了高强冷弯薄壁型钢构件按中国规范GB 50018-2002计算有效宽度的建议.

薄壁钢管混凝土短柱轴压力学性能试验研究

通过 2 6根圆形、方形和八边形薄壁钢管混凝土短柱的轴压试验 ,研究了不同截面形状、宽 (径 )厚比、混凝土强度等级、含钢率等参数对薄壁钢管混凝土短柱轴压力学性能的影响。试验表明 ,由于有内填混凝土的支撑作用 ,钢管壁的局部屈曲和屈曲后的性能有很大提高 ,与常规壁厚的钢管混凝土短柱的轴压破坏模式相比也有较大的变化。通过试验数据的回归分析 ,提出了薄壁钢管混凝土短柱极限轴心抗压承载力的实用计算公式 ,探讨了短柱的截面形状、宽厚比、混凝土强度等级。

矩形冷弯型钢钢管混凝土柱的力学性能研究

进行了8个冷弯型钢钢管混凝土构件的试验,表明其具有良好的力学性能。在确定组成矩形冷弯型钢钢管混凝土的钢材和核心混凝土应力-应变关系模型的基础上,利用数值解法对其轴压、纯弯和压弯构件的荷载-变形关系进行了全过程分析,分析结果与试验结果吻合良好。最后在参数分析的基础上,提供了轴压、纯弯和压弯构件承载力的实用计算方法。

C形冷弯薄壁型钢切割短柱轴压试验

把辊轧成型的C形冷弯薄壁型钢构件切割成若干短柱,在短柱中将产生不同程度的歪曲变形,进而引起附加的初始几何缺陷。对10个切割而成的C形冷弯薄壁型钢短柱进行了轴压试验,并根据GB500182002计算了短柱的轴压承载力。结果表明切割短柱在轴压力作用下,两翼缘为内收的歪曲破坏,腹板为局部屈曲破坏模式,短柱极限承载力仅为规范计算值的83%～89%。