Behaviour of concrete-filled double skin rectangular steel tubular beam-columns

Double skin composite columns are formed from two steel skins filled with concrete in between. This new form of hybrid column has the potential to be used in many domains such as high-rise bridge piers and large diameter columns in high-rise buildings, etc. This paper describes a series of tests carried out on concrete-filled double skin steel tubular (CFDST) stub columns, beams and beam-columns. Both outer and inner tubes are cold-formed rectangular hollow sections (RHS). The failure modes, and load-deformation behaviour of CFDST specimens are compared with those of conventional concrete-filled steel tubular members and empty double skin tubular members. A theoretical model is developed in this paper for the CFDST stub columns, beams and beam-columns. Reasonably good agreement is observed between the predicted and tested curves. Simplified models are derived to predict the load-carrying capacities of the composite members.     

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 square hollow steel tubes and steel tubes filled with concrete

This paper investigates the occurrence of local buckling in bare steel and concrete-filled tubes to study how different depth-to-thickness ratios affect the response of the steel component. The experimental set-up and results of 24 tests are presented in this paper. Specimens with values of depth-to-thickness ratios in the range of 50–125 have been considered. The presence of the concrete has been observed to affect the exhibited buckling mode and to significantly increase the buckling bearing capacity of the concrete-filled steel tubes. A numerical model has been developed using the commercial software ABAQUS and has been validated against the experimental results of this study. From a design viewpoint, it has been observed that local buckling needs to be included in the calculation of the contribution of the steel component to the bearing capacity of a concrete-filled tube when its depth-to-thickness ratio is over 50. For a slender plate, i.e., with a depth-to-thickness ratio over 120, its post-buckling behavior could be included in the calculation of the steel contribution as it evidently increases its bearing capacity. Finally, an equation for the calculation of the bearing capacity of composite sections with both stocky and slender steel elements has been proposed and validated against extensive experimental results available in the literature.     

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.     

Behavior of biaxially-loaded rectangular concrete-filled steel tubular slender beam-columns with preload effects

In composite construction, rectangular hollow steel tubular slender beam-columns are subjected to preloads arising from construction loads and permanent loads of the upper floors before infilling of the wet concrete. The behavior of biaxially loaded thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with preloads on the steel tubes has not been studied experimentally and numerically. In this paper, a fiber element model developed for CFST slender beam-columns with preload effects is briefly described and verified by existing experimental results of uniaxially loaded CFST columns with preload effects. The fiber element model is used to investigate the behavior of biaxially loaded rectangular CFST slender beam-columns accounting for the effects of preloads and local buckling. Parameters examined include local buckling, preload ratio, loading angle, depth-to-thickness ratio, column slenderness, loading eccentricity and steel yield strength. The results obtained indicate that the preloads on the steel tubes significantly reduce the stiffness and strength of CFST slender beam-columns with a maximum strength reduction of more than 15.8%. Based on the parametric studies, a design model is proposed for axially loaded rectangular CFST columns with preload effects. The fiber element and design models proposed allow for the structural designer to efficiently analyze and design CFST slender beam-columns subjected to preloads from the upper floors of a high-rise composite building during construction.     

Heat transfer in concrete-filled carbon and stainless steel tubes exposed to fire

Nowadays, performance-based design methods are increasingly used for fire resistance assessment of structures. To implement these methods, it is paramount to determine the temperature development within a structural member exposed to fire as accurately and efficiently as possible. Numerical models are developed in this paper to simulate the temperature development in concrete-filled carbon and stainless steel tubes. It was found that the influence of the moisture content in concrete and the thermal contact conductance at the steel–concrete interface is significant. New models for thermal conductivity of concrete and thermal contact conductance at the interface are proposed in this paper. Comparisons of temperature development are made between numerical simulations and extensive experimental results. Improved agreement with test results is achieved when the proposed models are used in the heat transfer analysis.     

Performance of concrete-filled thin-walled steel tubes under pure torsion

In practice, concrete-filled steel tubes (CFST) are often subjected to torsion. To date, such a problem however has not been addressed satisfactorily by design codes. The present study is thus an attempt to study the torsional behaviours of concrete-filled thin-walled steel tubes. ABAQUS software is used in this paper for the finite element analysis (FEA) of CFST subjected to pure torsion. A comparison of results calculated using this modelling shows good agreement with test results. The FEA modelling was used to investigate the influence of important parameters that determine the ultimate torsional strength of the composite sections. The parametric studies provide information for the development of formulae to calculate the ultimate torsional strength, as well as the torsional moment versus torsional strain curves of the composite sections.     

超声波在钢管混凝土检测中的运用

简要介绍了超声波检测的历史、声学原理以及脉冲超声波的声学参数,利用超声波脉冲在混凝土中传播的特性,应用到检测钢管混凝土主拱中去,经过分析,此方法准确、可靠,提出了可能产生的错误及相应的补救方法.     

Behavior of framed modular building system with double skin steel panels

A new type of lateral force-resisting system, a framed modular building with double skin steel panels of slender thin steel plates is presented. Modular construction leads to faster construction, improved quality and reduced resources and waste. A steel panel strengthened framed modular system is developed for the lateral load resisting system instead of in situ concrete core walls. The proposed double skin steel panel systems showed moderate ductility and energy dissipation due to their post-buckling strength. Full-scale experiments on a framed modular system with double skin steel panels were conducted. The test of the frame with steel panel systems showed that all steel panel systems reached a yielding point before the frame structure started to yield, so that severe damage to the frame as a primary structure was controlled. Also, the steel panel systems increased the initial lateral stiffness of the total system and maintained the elastic range of the panels up to near the yielding point of plates without local buckling driven from its shear behavior. By rigid-plastic analysis, the post-buckling strength of thin plates under in-plane bending was predicted and compared with experimental results. Based on the experimental data of the panels, the analytic model of these panel systems was constructed and compared with the experimental results of frames with double skin steel panel systems.     

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]     

方钢管混凝土粘结强度试验研究

为了研究方钢管混凝土柱的粘结滑移性能,进行了9个不同长细比、宽厚比的方钢管混凝土柱的推出试验。通过测量荷载、加载端和固定端的钢管与混凝土滑移,并根据试验结果得出了典型P-s曲线,分析了影响方钢管混凝土粘结强度的主要因素,可对方钢管混凝土粘结滑移性能的进一步试验研究和理论分析提供参考。     

Compressive and flexural behaviour of CFRP-repaired concrete-filled steel tubes after exposure to fire

This paper presents the results of axial compression and bending tests of fire-damaged concrete-filled steel tubes (CFST) repaired using unidirectional carbon fibre reinforced polymer (CFRP) composites. Both circular and square specimens were tested to investigate the repair effects of CFRP composites on them. The test results showed that the CFRP jackets enhanced the load-bearing capacity of the stub columns effectively. Enhancement of the columns’ stiffness due to the CFRP jackets was also observed. However, for beams, the test results demonstrated that the repair effect was not as good when compared with that for stub columns. From the test results, it is recommended that other appropriate repair measures should be taken in repairing severely fire-damaged CFST beams, or those members subjected to comparatively large bending moments.     

Effect of reinforcement stiffeners on square concrete-filled steel tubular columns subjected to axial compressive load

Eight stiffened square concrete-filled steel tubular (CFST) stub columns with slender sections of encasing steel and two non-stiffened counterparts were tested subjected to axial compressive load. Four types of reinforcement stiffeners and steel tensile strips were introduced to postpone local buckling of steel tubes, in which the tensile strip was first used as stiffener in CFSTs. The stiffening mechanism, failure modes of concrete and steel tubes, strength and ductility of stiffened square CFSTs were also studied during the experimental research. A numerical modeling program was developed and verified against the experimental data. The program incorporates the effect of the stiffeners on postponing local buckling of the tube and the tube confinement on concrete core. Extensive parametric analysis was also conducted to examine the influencing parameters on mechanical properties of stiffened square CFSTs.     

Flexural strength analysis of non-post-tensioned and post-tensioned concrete-filled circular steel tubes

Concrete-filled circular steel tubes (CFT) have recently gained significant attention for their enhanced strength and ductility over the conventional steel and reinforced concrete construction. The concrete compressive strength is significantly increased by the lateral confinement provided by the steel tube and local buckling of the steel tube is restrained by the concrete infill. This paper investigates the further enhancement of these composite actions due to post-tensioning the concrete cores inside circular steel tubes. The flexural behavior of a post-tensioned CFT as well as a non-post-tensioned CFT was studied experimentally and analytically. A numerical algorithm for predicting the moment capacities of circular CFT, with or without the post-tensioning effects, has been validated against the test results by the authors as well as those published in the literature.     

Experimental behaviour of stiffened concrete-filled thin-walled hollow steel structural (HSS) stub columns

Test results on concrete-filled steel tubular stub columns with inner or outer welded longitudinal stiffeners under axial compression are presented in this paper. The research was mainly focused on square hollow section (SHS) columns; two rectangular hollow section (RHS) columns were also tested. A longitudinal stiffener was provided on each side of the stiffened SHS column, while only two stiffeners were welded to the longer sides of the stiffened RHS column. The main experimental parameters considered were the height-to-thickness ratio and stiffener rigidity. In addition, empty tubes with or without stiffeners, as well as unstiffened concrete-filled steel tubes were also tested for comparison. Requirements for stiffener rigidity are developed by modifying a formula presented in the literature. Existing theoretical model and design codes were used to predict the load versus axial strain relationships and load-carrying capacities of the adequately stiffened composite sections respectively; reasonable results were achieved.     

Axial strength of circular concrete-filled steel tube columns — DOE approach

This paper presents the effect of changes in diameter of the steel tube (D), wall thickness of the steel tube (t), strength of in-fill concrete (f_cu), and length of the tube (L) on ultimate axial load (P_ue) and axial shortening at the ultimate point (δ_ue) of circular Concrete Filled steel Tubes (CFT). Taguchi’s approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the axial load and the axial shortening at the ultimate point. A total of 243 circular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-2005 and EC4-1994.     

圆中空夹层钢管混凝土柱承载力研究

采用统一强度理论，对圆中空夹层钢管混凝土柱进行了研究，分析了钢管的拉压强度比，及中间主应力对圆中空夹层钢管混凝土柱承载力的影响，提出了圆中空夹层钢管混凝土柱的极承载力计算公式，与文献资料的试验结果作了比较，验证了理论公式的正确性，并得出了中空夹钢管混凝土柱和钢管混凝土具有相同优点等结论。该结果为中空夹层钢管混凝土柱的承载力分计算提供了一定的理论依据，对工程设计有一定的参考价值。以限层析     

钢管混凝土结构的特点及其发展前景

指出钢管混凝土结构能够充分发挥钢管和混凝土两种材料的优点,且具有强度高、重量轻、抗震性能好等优点,介绍了钢管混凝土结构的特点、研究现状及其工程应用,探讨了钢管混凝土结构的研究方向,以推广钢管混凝土结构的应用。     

八边形中空夹层钢管混凝土轴压短柱力学性能的研究

在总结圆中空夹层钢管混凝土和方中空夹层钢管混凝土柱受力性能与工程应用优缺点的基础上,提出采用八边形中空夹层钢管混凝土结构的合理性。对八边形中空夹层钢管混凝土轴压短柱力学性能进行试验分析,得到构件各组成部分的荷载-应变关系曲线和极限承载力值,由试验现象与试验结果发现八边形截面中空夹层钢管混凝土柱的承载能力比方形截面柱承载能力高,比圆形截面柱承载能力稍低,且与八边形直边与斜边之比相关。为拓展此类构件应用的几何尺寸范围,在确定材料合理的应力-应变关系模型后,采用有限元方法进一步分析此类构件的力学性能,由此得到的荷载-应变关系曲线以及构件承载力与试验结果能较好地吻合。通过对影响构件承载能力各主要参数的分析,利用试验与数值模拟结果,提出轴压条件下八边形中空夹层钢管混凝土短柱极限承载力的计算公式,供工程设计人员参考。