Behaviour of tapered concrete-filled double skin steel tubular (CFDST) stub columns

Recently, tapered concrete-filled double skin steel tubular (CFDST) columns have been applied in electricity transmission towers in China. However, there is still lack of information on the behaviour of such kind of members. This paper thus carried out the investigation on axially loaded tapered CFDST stub columns. The parameters included the tapered angle and the sectional profile. A finite element analysis (FEA) model was developed to predict the behaviour of the tapered member as well. The results showed that the steel tubes and the sandwiched concrete could work together well despite the tapered angle. The failure mode of the tapered CFDST stub column was similar to that of the straight one, and the failure occurred near the smallest section. The confinement effect of the tapered member was discussed by using the stress analysis. Finally, formulas were suggested for the calculation on the ultimate strength of the tapered CFDST stub column.     

Analytical behaviour of concrete-filled double skin steel tubular (CFDST) stub columns

This paper reports a finite element analysis of the compressive behaviour of CFDST stub columns with SHS (square hollow section) or CHS (circular hollow section) outer tube and CHS inner tube. A set of test data reported by different researchers were used to verify the FE modelling. Typical curves of average stress versus longitudinal strain, stress distributions of concrete, interaction of concrete and steel tubes, as well as effects of hollow ratio on the behaviour of CFDST stub columns, were presented. The influences of important parameters that determine sectional capacities of the composite columns were investigated.     

标准火灾作用下钢管混凝土短柱落锤动态冲击试验研究

采用落锤冲击实验机进行ISO-834标准火灾作用下钢管混凝土短柱抗冲击性能试验研究,考察受火时间、冲击速度、冲击能量和含钢率对其抗冲击性能的影响。试验量测钢管表面温度、冲击力与压缩变形时程曲线。试验结果表明,受火时间、冲击速度、冲击能量和含钢率均对高温下钢管混凝土的动态力学性能有影响;受火时间对冲击极限承载力和残余变形的影响最为显著,其余参数对冲击承载力影响不大,而试件的残余变形随着受火时间和冲击能量的增大而增大,随着含钢率的增大而减小。常温和火灾下钢管混凝土在冲击荷载作用下产生显著的压缩变形,遭受不同程度的破坏,但仍能够保持很好的截面完整性,说明钢管混凝土在火灾(高温)下具有良好的抗冲击能力,适用于有火灾(高温)抗冲击、抗倒塌设计需求的结构。     

Fire behaviour of high strength self-consolidating concrete filled steel tubular stub columns

This paper reports an investigation into the behaviour of high strength SCC (self-consolidating concrete) filled steel tubular stub columns exposed to standard fire. A series of tests were carried out to obtain the temperature distribution, axial deformation, limiting temperature of steel and fire endurance of the SCC filled steel tubular stub columns. In addition, a finite element analysis (FEA) model was proposed and used to simulate the fire behaviour of the columns. In the FEA modeling, a sensitivity study was conducted to determine the concrete fracture energy and the contact property of the steel and concrete interface. The verified FEA model was used to analyse the structural behaviour of the columns under fire exposure, such as strain, stress, the load sharing between the steel tube and concrete and local buckling of the steel tube, to gain an insight into the failure mechanism of the columns.     

Fire performance of self-consolidating concrete filled double skin steel tubular columns: Experiments

An investigation into the fire performance of self-consolidating concrete (SCC) filled double skin tubular columns (CFDST) during the standard fire test is reported. Six full size SCC filled CFDST columns were designed for the fire tests. Detail failure modes of overall specimens and each component in the columns as well as temperatures, deformation and fire endurance were presented. Fire performance of the CFDST columns were studied through analysis of the limiting temperature of the outer tube, composite action between steel and concrete and effect of a number of parameters on the fire endurance. It showed that the limiting temperature in the CFDST columns is significantly higher than that in concrete filled steel tubular (CFST) columns or critical temperature in steel structural components. Strong evidence was found to prove the existence of composite action between steel and concrete in the CFDST columns during fire exposure. Effect of a number of parameters on the fire endurance of the composite columns was identified. Investigation into the fire performance of the columns also reveals possible solutions to improve the fire resistance of CFDST members.     

Behaviour of concrete-filled steel tubular stub columns subjected to axially local compression

The behaviour of concrete-filled steel tubular (CFST) stub columns subjected to axially local compression was experimentally investigated in this paper. A total of thirty-two specimens were tested. The main parameters varied in the tests are: (1) sectional types: circular and square; (2) local compression area ratio (concrete cross-sectional area to local compression area): 1.44 and 16; and (3) thickness of the endplate: from 2 to 12 mm. A finite element analysis modelling was used for the analysis of CFST stub columns subjected to axially local compression, and a comparison of results calculated using this modelling shows generally good agreement with the test results. The theoretical modelling was then used to investigate the mechanism of the composite columns subjected to axially local compression.     

Experimental investigation on concrete-filled stainless steel stiffened tubular stub columns

This paper presents an experimental investigation on concrete-filled normal-strength stainless steel stiffened tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). The stiffened stainless steel tubes were fabricated by welding four lipped angles or two lipped channels at the lips. Therefore, the stiffeners were formed at the mid-depth of the sections. In total, five hollow columns and ten concrete-filled columns were tested. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to behave as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. A series of tests was performed to investigate the effects of cross-section shape and concrete strength on the behavior and strength of concrete-filled stainless steel stiffened tubular stub columns. The measured average overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. Different lengths of columns were selected to fix the length-to-depth ratio to a constant value of 3. The concrete-filled stiffened stainless steel tubular columns were subjected to uniform axial compression over the concrete core and the stainless steel tube to force the entire section to undergo the same deformations by blocking action. The column strengths, load–axial strain relationships and failure modes of the columns are presented. Several comparisons were made to evaluate the test results. The results of the experimental study showed that the design rules, as specified in the European specifications and the ASCE, are highly conservative for square and rectangular cold-formed concrete-filled normal-strength stainless steel stiffened stub columns.     

Finite element modelling of concrete-filled lean duplex stainless steel tubular stub columns

This paper presents a finite element (FE) study on concrete-filled lean duplex slender stainless steel tubular (CFDSST) stub columns of square and L-, T-, and +-shape (Non-Rectangular Sections or NRSs) sections under pure axial compression. The effect of cross-sectional shape and concrete compressive strength, by considering equal steel consumption (i.e. equal cross-sectional area) for all the square and NRSs sections have been reported. In CFDSST stub columns, the axial deformation (δ _u ) at ultimate load (P _u ) decreases with increasing concrete strengths, but increases as the sections changes from Square→L→T→+-shape. For normal concrete strength (≤40 MPa), NRSs appear to have similar or slightly enhanced P _u , in comparison with the representaive square section. But in the case of a high strength concrete core (i.e. >40 MPa), NRSs are clearly at a disadvantage as far as the values of P _u is concerned, however as the NRSs are lighter by 37%, they still offer an attractive option for the designers. The FE strengths over predicts the EN 1994-1-1 (2004) specification by about an average of 21, 19, 14, and 4% for the square, L, T, and +-shape sections, respectively.     

多边形空心钢管混凝土轴压短柱非线性分析

在轴压试验结果的基础上,选择合理的材料本构关系模型,应用大型通用ANSYS有限元软件对四边形和八边形空心钢管混凝土短柱进行了有限元模拟,着重讨论了有限元模型的建立方法,并通过模拟结果与试验结果的对比,验证了有限元模型的合理性。     

Numerical modelling of concrete-filled lean duplex slender stainless steel tubular stub columns

Major technological advances in materials processing have led to the development of duplex stainless steels with exceptional mechanical properties. Duplexes have great potential for expanding future structural design possibilities, enabling a reduction in section sizes leading to lighter structures. The duplex grades offer combination of higher strength than austenitics as well as a great majority of carbon steels with similar or superior corrosion resistance. However, high nickel prices have more recently led to a demand for lean duplexes with low nickel content, such as grade EN 1.4162. Extensive work is needed to include the lean duplex grade EN 1.4162, into design standards such as EN 1993-1-4 and ENV 1994-1-1. Accordingly, finite element modelling for concrete-filled lean duplex slender stainless steel tubular stub columns of Grade EN 1.4162 is presented in this paper. The paper is predominantly concerned with two parameters: cross-section shape and concrete compressive strength, which have not yet been investigated. The non-linear displacement analysis of the columns was constructed herein based on the confined concrete model provided by Hu et al. (2003) [15]. The behaviour of the columns was investigated using a range of concrete cylinder strengths (25–100 MPa). The overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. The concrete-filled lean duplex slender stainless steel tubular columns were subjected to uniform axial compression over the concrete and stainless steel tube to force the entire section to undergo the same deformations by blocking action. The ABAQUS 6.6 program, as a finite element package, is used in the current work. The results showed that the design rules specified in the ASCE are highly conservative for square and rectangular concrete-filled lean duplex slender stainless steel stub columns while they are conservative in the case of European specifications. A new design strength is, therefore, proposed that is accurately found to represent the behaviour of concrete-filled lean duplex stainless steel tubular stub columns.     

Confinement effect of stiffened and unstiffened concrete-filled stainless steel tubular stub columns

This paper presents a comparative study between stiffened and unstiffened concrete-filled stainless steel hollow tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). Finite element analysis of concrete-filled stainless steel unstiffened tubular stub columns is constructed herein based on the confined concrete model recently available in the literature. It is then compared with the experimental results of concrete-filled stainless steel stiffened tubular stub columns. The stiffened stainless steel tubular sections were fabricated by welding four lipped angles or two lipped channels at the lips. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to act as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. The overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. The stiffened and unstiffened concrete-filled stainless steel tube specimens were subjected to uniform axial compression over the concrete and stainless steel tube to force the entire section to undergo the same deformations by blocking action. The ABAQUS 6.6 program, as a finite element package, is used in the current work. The results of the comparative study showed that the stainless steel tubes in stiffened concrete-filled columns offered a high average of increase in the confinement of the concrete core than that of the unstiffened concrete-filled columns.     

圆钢管高强混凝土轴压短柱受剪承载力分析

为了深入研究钢管高强混凝土轴压短柱破坏模式与破坏机理,提出适合钢管高强混凝土轴压短柱极限承载力计算方法,针对圆钢管高强混凝土轴压短柱大都发生剪切破坏这一典型现象,引入莫尔-库仑强度理论,从理论上分析其发生剪切破坏的原因和受力机理,并从剪切破坏的角度提出了钢管高强混凝土轴压短柱承载力计算方法。利用基于圆钢管高强混凝土轴压短柱试验研究和有限元分析回归得到的处于复杂应力场中的钢管纵向应力σv-纵向应变ε关系曲线和钢管横向应力σh-纵向应变ε关系曲线的数学表达式,得到了钢管高强混凝土轴压短柱承载力包络线的简化计算方法,简化计算曲线与试验曲线吻合良好,可用于分析钢管高强混凝土轴压短柱的受剪承载力。     

Analysis of circular concrete-filled double skin tubular slender columns with external stainless steel tubes

This paper investigates the strength and behaviour of concrete-filled double skin steel tubular (CFDST) slender columns under axial compression. The lean duplex stainless steel material (EN 1.4162) which has recently gained significant attention is considered herein as the external jacket of such columns. Finite element (FE) analyses of several CFDST columns are conducted. Careful consideration is taken in the modelling for the concrete behaviour, for which both of the compressive and the tensile behaviours and the non-linear behaviour due to cracking are fully considered. The accuracy of the current FE models is ensured through the comparison with the existing columns in literature. A parametric study is then conducted to investigate the behaviour of such columns under different affecting factors; the slenderness ratio, the concrete confinement effect, the hollow ratio, the concrete compressive strength and the thickness ratio. The behavioural differences between intermediate length and very long CFDST columns are carefully addressed. Analytically obtained ultimate strengths are compared with design strengths calculated by European and American specifications. European design strength is found to give better predictions compared to the American specifications. However, it is shown that both strengths cannot be used in design because they overestimate the ultimate strengths and thereby do not satisfy the safety requirements. Therefore, a modification is suggested to the European design model which is shown to be able to estimate the compressive resistance of the CFDST columns more accurately than other methods.     

Behavior of concrete-filled double skin steel tubular columns with octagon section under axial compression

Based on some conclusions of two kinds of concrete-filled double skin steel tube (CFDSST) members with circular or square sections, a new kind of CFDSST with octagonal section, where the outer tube has an octagonal section and the inner tube has a circular section, is proposed in this paper. Behaviors of the CFDSST members with octagon section subjected to axial compression are investigated, and some curves of load-strain of steel tubes and confined concrete and the bearing capacity of members are obtained. It is indicated that the bearing capacity of the columns with octagonal section is larger than that with square section and is smaller than that with circular section, and the bearing capacity of members is related to the ratio of the straight side to the bevelled one. Based on the proper stress-strain relationship, a couple of numerical analyses are made using the finite element software named ANSYS. Finally, a simplified formula is proposed in the paper, and the numerical results agree well with the experimental results and the mathematical solutions. The results are valuable for engineers.     

Mechanical behavior of stirrup-confined circular concrete-filled steel tubular stub columns under axial loading

通过井字形拉筋、米字形拉筋和圆环箍筋等3组拉筋约束形式带拉筋圆钢管混凝土短柱轴压性能对比试验,研究不同拉筋约束形式、拉筋体积配箍率对圆钢管混凝土轴压短柱的承载力和延性等的影响;采用合理的混凝土三轴受力本构模型和钢材本构模型,应用ABAQUS非线性有限元分析软件对带拉筋圆钢管混凝土轴压短柱进行三维有限元分析,有限元计算结果与试验结果吻合较好;在此基础上,分析了带拉筋圆钢管混凝土轴压短柱中钢管、拉筋或箍筋、核心混凝土之间的组合作用。结果表明：井字形拉筋圆钢管混凝土轴压短柱的承载力最高,延性最好,钢管、拉筋和核心混凝土之间的组合作用最强;提高体积配箍率可以有效提高圆钢管混凝土短柱的轴压承载力和延性。     

Behavior of concrete-filled double skin steel tubular columns with octagon section under axial compression

Based on some conclusions of two kinds of concrete-filled double skin steel tube (CFDSST) members with circular or square sections, a new kind of CFDSST with octagonal section, where the outer tube has an octagonal section and the inner tube has a circular section, is proposed in this paper. Behaviors of the CFDSST members with octagon section subjected to axial compression are investigated, and some curves of load-strain of steel tubes and confined concrete and the bearing capacity of members are obtained. It is indicated that the bearing capacity of the columns with octagonal section is larger than that with square section and is smaller than that with circular section, and the bearing capacity of members is related to the ratio of the straight side to the bevelled one. Based on the proper stress-strain relationship, a couple of numerical analyses are made using the finite element software named ANSYS. Finally, a simplified formula is proposed in the paper, and the numerical results agree well with the experimental results and the mathematical solutions. The results are valuable for engineers. __________ Translated from China Civil Engineering Journal, 2007, 40(2): 33–38 [译自: 土木工程学报]     

Behavior of concrete-filled rectangular weathering steel tubular stub columns under axially compressive loading

为了研究耐候钢管混凝土轴压短柱的受力性能,开展了矩形截面形式共4根耐候钢管混凝土轴压短柱试验研究,采用有限元法对试验轴压短柱性能进行了建模分析。结合试验和有限元法,分析比较耐候钢管混凝土轴压短柱与普通钢管混凝土轴压短柱受力性能的差异。研究结果表明：耐候钢材拉伸性能试验表明耐候钢材与碳素钢的力学性能相似,文中采用的钢材本构关系对耐候钢适用;设置约束拉筋使得构件承载力、延性以及钢管对混凝土的约束作用均有提高;耐候钢管混凝土短柱试验研究、有限元分析结果均表明耐候钢管混凝土短柱轴压性能与普通钢管混凝土无显著差异。