Behavior of Two-Chord Steel–Concrete Composite Columns under Axial Compression (original) (raw)
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This paper investigates the behaviour of concentrically axially loaded circular and square high strength steel tube (Fe310 grade) columns filled with different grades (M20, M30 & M40 etc.) of concrete. The effects of grade of concrete and composite action between the steel tube and the concrete core on axial load capacity are studied & graphs of Axial load v/s vertical deflection (axial shortening curves) are plotted experimentally. Some important performance indices entitled as Ductility Index (DI), Strength factor (SI) and Concrete Contribution Ratio(CCR) are also evaluated and compared between the circular and the square shaped Concrete Filled Steel Tube (CFST) columns.By referring many research works, we can know firmly that confinement effect is restricted to short column only. So, we choose 300mm length for all the specimens of 88.9mm dia and 80×80mm size, to keep the columns stub only for getting benefit of confinement effect especially in circular sections.From the results, it has been noted that square columns have higher axial capacity when compared with circular columns of same resisting area under compression. Hence, size reduction for square column is possible. While ductility index for circular columns are quite better than square ones. Ultimate failure patterns are obtained by applying axial compression loads concentrically up to ultimate stage on circular and square CFST stub columns. as expected, the results shows a Local buckling i.e. crushing of concrete type of failure at supports. Ultimate axial load capacity of Concrete filled steel tubular columns are evaluated and compared experimentally as well as by calculations also, as per the guidelines suggested by EC4(Eurocode part-4, British Standards Institutions) code, which is the best suitable code for design of CFST columns amongst all other international codes for composite structure design. From the study it is concluded that, loads obtained by EC4 fits nearer to perfection and depicts the behaviour well enough by 15-20% error with experimental ultimate loads. The results obtained by experimental and EC4 code are validated well with the previous scholar researchers too
Comparative Study of Concrete Filled Steel Tube Columns under Axial Compression
International Journal of Constructive Research in Civil Engineering
In recent days, due to the expansion of cities it is required to construct the high storey buildings. Composite buildings prove to be promising for multi storey building. As a result, composite columns have recently undergone increased usage throughout the world, which has been influenced by the improvement of high strength concrete enabling these columns to be considerably economized. Columns are designed to resist the majority of axial force by concrete alone can be further economized by the use of thin walled steel tube. The paper discusses about the behavior of the composite column and various codal provisions. Experimental research carried out by comparative study between experimental results and analytical results for hollow steel tube (HST) and concrete filled steel tubes (CFST) under axial compression. To compare the experimental results of CFST with AISC-LRFD 2005 and Eurocode-4. The investigation is carried out on HST & CFST specimens of Rectangular cross section with three different sizes. The grade of concrete used for infill concrete is M20 and M40. The tests on said CFST specimens are carried out with the help of compression testing machine. The axial load is applied gradually on specimens. This paper presents the details of study carried out and the conclusions arrived.
Engineering Structures, 2010
On the basis of the theory of elasticity, a unified formulation is proposed in this paper to predict the composite compressive strength of circular concrete-filled steel tube (CCFST) columns. The formula is obtained from the analytic solution of an elastic composite cylinder under axial compression. The formula is further calibrated by introducing a number of correlation coefficients that are validated by test results. Furthermore, the stability factor of CCFST long columns under axial compression is derived on the basis of the Perry-Robertson formula. The newly derived formulas of stability bearing capacity are applicable for both hollow and solid CCFST columns, which is again validated through comparisons with experimental results. One of the important features of the new formulas is that they provide a unified formulation for both hollow and solid CCFST columns that relates the compressive strength or the stability capacity of a CCFST column and a series of design parameters.
Marine Structures, 2019
Concrete-Filled Steel Tube (CFST) columns combine the benefits of high ductility and tensile strength of steel with high stiffness and compressive strength of concrete. It can be used in marine structures. This paper presents the mechanical performance of CFST columns strengthened by steel Reinforcing Bars (RBs) under axial compression. A series of experiments were carried out on 22 CFST columns using two different D/t ratios and different patterns of RBs as parameters. Furthermore, different diameters and numbers of RBs were utilized. The RBs were either welded on the internal surface of the steel tubes or embedded within concrete as a reinforced concrete. Various patterns were used to enable a better understanding of the strengthened CFST columns performance. Moreover, the compressive loading vs. end shortening curves, failure modes, strength index and RBs contribution ratio were analysed. The design methods of the ordinary CFST columns (EC4, AISC, Han, Yu, and Liang) were modified and assessed against the experimental results to trace the suitable formulation for design purposes. According to the theoretical results, the analytical formulations of certain methods are acceptable for the analysis of reinforced and stiffened CFST columns.
Proceedings of the 7th International Conference on Civil, Structural and Transportation Engineering (ICCSTE'22)
This paper presents an experimental investigation on circular concrete-filled double steel tubular (CFDST) slender columns under axial loading. The test parameters include the column slenderness ratio and the thickness of the inner steel tube. Test results show that the common failure mode of CFDST slender columns is the global failure of the columns. It is found that increasing the column slenderness decreases the ultimate strengths of the columns and the thickness of the inner steel has an insignificant influence on the ultimate strength of the columns. The design model specified by Eurocode 4 for conventional CFST slender columns is shown to overestimate the ultimate strength of CFDST slender columns under axial loading.
Performance of Concrete Filled Steel Tubular Columns
Recent advancements in the availability of higher strength steels, better coating materials for protection and high strengths/performance concretes have expanded the scope of concrete filled steel composite columns with wide ranging applications in various structural systems with ease of construction, highly increased strengths and better performance. This experimental study is carried out on the behavior of short, concrete filled steel tubular columns axially loaded in compression to failure. Three dimensional confinement effect of concrete along with support provided by concrete to the thin walls of steel tube to prevent local buckling had a composite effect on the strength of the composite column increasing the compressive strengths by almost 300 to 400%. In addition to the concrete core, the parameters for the testing were shape of the steel tube and its diameter-to-thickness ratio. It has been observed that ultimate strength of concrete filled steel tubes under concentric compression behavior is considerably affected by the thickness of the steel tube, as well as by the shape of its cross section. Confining effect in circular CFST columns improves their strength, appreciably. The axial load-deformation behavior of columns is remarkably affected by the cross-sectional shape, diameter/width-to-thickness ratio of the steel tube, and the strength of the filled concrete. The load deformation relationship for circular columns showed strain-hardening or elastic perfectly plastic behavior after yielding.
A COMPARATIVE STUDY ON SQUARE AND CIRCULAR HIGH STRENGTH CONCRETE-FILLED STEEL TUBE COLUMNS
This paper investigates the behavior of axially loaded square and circular high strength concrete-filled steel tube (CFST) columns. The effects of steel tube thickness and bond strength between the steel tube and the concrete core on axial load capacity and ductility are studied. The performance indices named ductility index (DI), strength enhancement index (SI) and concrete contribution ratio (CCR) are also evaluated for the square and the circular high strength CFST columns. The experimental results are compared with the values estimated by current design codes such as Eurocode 4 (EC4) and AISC-LRFD (1999). The results show that the difference of the axial load capacity due to loss of bonding is significant for both of the square and the circular high strength CFST columns. However, this difference is equal for both of the square and the circular columns with H/t or D/t smaller than 20. The EC4 design code, contrary to the AISC-LRFD (1999), generally overestimates the axial load capacity of the square and the circular high strength CFST columns.
Engineering Structures, 2013
Current design practice of concrete-filled steel tube (CFST) columns uses different formulas for different section profiles to predict the axial load bearing capacity. It has always been a challenge and practically important issue for researchers and design engineers who want to find a unified formula that can be used in the design of the columns with various sections, including solid, hollow, circular and polygonal sections. This has been driven by modern design requirements for continuous optimization of structures in terms of not only the use of materials, but also the topology of structural components. This paper extends the authors' previous work [1] on a unified formulation of the axial load bearing capacity for circular hollow and solid CFST columns to, now, including hollow and solid CFST columns with regular polygonal sections. This is done by taking a circular section as a special case of a polygonal one. Finally, a unified formula is proposed for calculating the axial load bearing capacity of solid and hollow CFST columns with either circular or polygonal sections. In addition, laboratory tests on hollow circular and square CFST long columns are reported. These results are useful addition to the very limited open literature on testing these columns, and are also as a part of the validation process of the proposed analytical formulas. Keywords：Concrete-filled steel tube (CFST), hollow and solid section, circular and polygonal section, load bearing capacity Notations sc f combined strength of CFST sc ϕ stability factor of CFST 0
Structures, 2019
External confinement and internal stiffening have been widely adopted for strengthening concrete-filled steel tube (CFST) columns. This paper presents an attempt to study the possibility of combining the external confinement using reinforcing rings and the internal stiffening using reinforcing bars for strengthening CFST columns. In order to investigate the structural performance of the proposed combination method, a total of 18 specimens were tested under axial compression. These specimens were strengthened using three different methods: confinement in the form of external reinforcing rings (ERRs), stiffening in the form of internal reinforcing bars (IRBs), and a combination of both methods. For all tested specimens, the thickness of steel tube, outer diameter, and tube length were 4.15 mm, 114.3 mm, and 260 mm, respectively. CFST specimens were filled using self-compacting concrete (SCC) of normal compressive strength. The main parameters considered in the test procedure are the spacing between the ERRs, the number of IRBs, and a combination of the ERRs spacing and the number of IRBs. The experimental results show that the proposed combination method is more effective to improve the structural performance of short CFST columns compared to using only ERRs or IRBs. Further improvement is achieved when the spacing between the ERRs decreases and the number of IRBs increases. The proposed combination method increases the compressive load-carrying capacity up to 27.2% and 57.4% compared to ERRs and IRBs, respectively. It deserves noting that the proposed combination method, ERRs, and IRBs improve the compressive load-carrying capacity up to 120.3%, 93.5%, and 40%, respectively, compared to the control specimen. In addition, specimens strengthened by the proposed combination method show an excellent ductility behavior.