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Load versus displacement curves for specimens with different stiffener configurations: (a) B/t = 64, (b) B/t = 88 and (c) B/ t = 112.
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As China’s infrastructure grows rapidly, the use of concrete-filled steel tubular structures for engineering applications is attracting increasing interest owing to their high section modulus, high strength and good seismic performance. However, for concrete-filled steel tubular members with large width-to-thickness ratio, steel tubes are prone to...
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Citations
... However, owing to the square steel tube wall could not provide effective confinement to the core concrete as that of the circular ones, ductility of square CFST columns is significantly weaker than their circular counterparts, particularly when they are in service under high level of axial loads (Yuan et al., 2023). Thus, to address the insufficient ductility concerns of square CFST columns, many well-known stiffening measures have been suggested by a wide range of previous studies, including (i) installing the bidirectional bond bars (Cai and He, 2006;Ding et al., 2018), (ii) welding shear connections (Wang et al., 2012), (iii) welding steel tie-bars , (iv) welding the longitudinal stiffeners (Tao et al., 2007;Yuan et al., 2019aYuan et al., , 2019b, (iv) adding the internal circular steel or FRP tube (Li et al., 2011;Feng et al., 2015;Ekmekyapar and Hasan, 2019), and (v) placing the steel spirals inside the tube (Ding et al., 2014(Ding et al., , 2020Zheng and Chen, 2015;Hu et al., 2020aHu et al., , 2020bTeng et al., 2021;Chen et al., 2021;Yuan et al., 2022aYuan et al., , 2022bYuan et al., , 2023. Among these measures, the former three could relatively helpful in delaying the steel tube local buckling, but may less effective in enhancing the confinement made by the steel tube to the core concrete. ...
Owing to the inherited structural defects of recycled aggregate concrete (RAC), such as deficiencies in durability and mechanical properties, its further applications in modernized civil engineering practices are significantly limited. To this end, this study aims to achieve the sustainable application of RAC and improve its mechanical properties by infilling it into the steel tube to form the recycled aggregate concrete filled steel tubular columns (RA-CFST columns). Numerous studies have indicated that embedding steel spiral stirrups inside the steel tube is helpful in improving the ultimate strength (Nu) and ductility of square CFST columns. Thus, this paper designed several square RA-CFST columns confined by high-strength steel (HSS) spiral stirrups (HSS-RA-CFST columns) and their concentric and eccentric compression behavior were experimentally studied. The test specimens were divided into two different parts, including (i) axial compression and (ii) eccentric compression test specimens. For the former, 16 columns were designed, including 4 traditional non-confined RA-CFST columns, 4 normal-strength steel (NSS) spiral-confined RA-CFST columns (NSS-RA-CFST columns), and 8 HSS-RA-CFST columns. For the latter, 8 specimens were prepared, including 2 non-confined and 6 HSS-RA-CFST columns. Effects of the critical test parameters, such as the steel tube thickness, steel spiral pitch, replacement ratio of recycled aggregate (RA) to natural aggregate (NA), and eccentricity ratio on the compression behavior of the specimens were examined. Subsequently, the failure modes, load-deflection responses, strain distributions, ductility, and the composite confinement mechanism of the columns were comprehensively studied. Finally, this paper also suggested the
improved design models in predicting the Nu of the spiral-confined CFST columns (i.e., NSS-RA-CFST and HSS-RA-CFST columns), and the effectiveness and accuracy of the recommended design models were validated by using the experimental results acquired from this study and those studies collected from the literature. This study could serve as the experimental and theoretical references for the mechanical properties and determination of the Nu for the spiral confined-RA-CFST columns under both the concentric and eccentric compression.
... In order to strengthen the performance of square concrete-filled steel tubular (CFST) columns, many scholars have suggested a variety of structural schemes, such as installing binding bars [1,2], welding tie bars [3], welding shear studs [4] and welding longitudinal stiffeners [5][6][7]. Although these approaches are effective in solving the local buckling of steel tube, the ability to improve the confinement effect of square steel tube is weak. ...
In this paper, eccentric compression behavior of square CFST columns with inner spiral stirrup was investigated. First, an eccentric compression test was conducted on 18 CFST columns with influential variables of the spiral pitch, the diameter-width ratio, the slenderness ratio, the eccentricity ratio, the longitudinal rebar ratio and the tube thickness. Test results showed that the spiral stirrup avoided the rapid loss of bearing capacity caused by excessive local deformation of the CFST column under eccentric compression. The performance of CFST columns with inner spiral stirrup can be improved by reducing the spiral pitch and increasing the diameter-width ratio. With the increase of the slenderness ratio and the eccentricity ratio, the ability of spiral stirrup to improve the eccentric compression behavior of CFST columns was significantly weakened. Before the peak load, the strain distribution of the steel tube along the section depth basically conformed to the plane section assumption, and the maximum strain of the spiral stirrup appeared near the corner of the steel tube in the compression zone. Furthermore, a parameter study using the fiber model method was performed to investigate the influence of steel distribution, including a spiral stirrup, longitudinal rebar and steel tube, on the bearing capacity of columns. It is found that the order of contribution efficiency of increasing the steel ratio of each component to the eccentric bearing capacity was spiral stirrup > steel tube > longitudinal rebar. Moreover, a finite element model was established for further analysis of the failure process. Finally, the recommendations on steel distribution and the formulas for calculating the eccentric load-carrying capacity were provided.
... To address the insufficient ductility of square CFST columns, various measures have been proposed in a series of studies [15][16][17][18][19][20][21] to improve their ductile performance, such as installing the bidirectional bond bars [15,16], welding shear connectors [17], welding steel tie-bars [18], and welding the longitudinal stiffeners [19][20][21]. These aforementioned measures are relatively helpful in delaying the local buckling of the steel tube, but may less effective in improving the confining ability of the steel tube to the core concrete. ...
... To address the insufficient ductility of square CFST columns, various measures have been proposed in a series of studies [15][16][17][18][19][20][21] to improve their ductile performance, such as installing the bidirectional bond bars [15,16], welding shear connectors [17], welding steel tie-bars [18], and welding the longitudinal stiffeners [19][20][21]. These aforementioned measures are relatively helpful in delaying the local buckling of the steel tube, but may less effective in improving the confining ability of the steel tube to the core concrete. ...
Ductility of square concrete filled steel tubular (CFST) columns is generally significantly lower than that of circular ones, especially when they are under high level of axial loads. Many previous studies suggested that adding internal steel spiral stirrups is an effective measure to improve ductility of square CFST columns. To investigate the effect of high-strength steel (HSS) spirals on the seismic behavior of the HSS spiral-confined CFST (HSS-CFST) columns under high axial load ratio, 15 square CFST columns, including 3 conventional CFST columns without internal steel spirals, 3 normal-strength steel (NSS) spiral-confined CFST (NSS-CFST) columns, and 9 HSS-CFST columns were experimentally studied through the cyclic loading tests. The critical test parameters included the steel spiral pitch and axial load ratio. Final failure modes, hysteretic response, skeleton curves, strain distributions , ductility, energy dissipation capacity, and stiffness degradation of the specimens were investigated in detail. The experimental results indicated that (i) apparent outwardly local bucking of the steel tube and core concrete crushing were observed for all specimens in the plastic hinge regions at the ultimate state; (ii) adding both the NSS and HSS spirals would beneficial in improving the hysteretic behavior and energy dissipation capacity of square CFST columns, but contributions to these improvements made by the HSS spirals were more significant than that of the NSS ones; (iii) the increase of axial load ratio and internal steel spiral pitch would impair the load-carrying capability and ultimate deformation ability of square CFST columns; (iv) ductility of the NSS-CFST and HSS-CFST columns could be improved as the increased of spiral volume ratio and the ductility enhancement was more pronounced in the HSS-CFST columns; and (v) the internal steel spirals were helpful in delaying the stiffness degradation rate of square CFST columns, particularly for those specimens under a high axial load ratio of 0.8.
... To solve the problem of inadequate ductile performance of square CFST columns, a number of researchers have proposed various measures to improve the stability of the steel tube wall, such as installing bidirectional binding bars [14,15], welding steel tie-bars [16], welding shear studs [17], and welding longitudinal stiffeners [18][19][20], as shown in Fig. 1. These measures could delay the buckling of steel tubes locally; however, they were less helpful in improving the confinement effectiveness of the steel tubes filled with concrete: the ductility of the CFST columns increased only marginally. ...
The ductility of concrete-filled steel tubular (CFST) columns with square cross-sections is significantly lower than circular ones when subjected to large axial forces or when thin-walled steel tubes and high-strength concrete are employed. The additional confinement contribution of the internal steel spiral compensates for the shortcomings of the rapid reduction of the ductility and strength of square CFST columns. The axial compressive performance of high-strength steel (HSS) spiral-confined square CFST (HSS-CFST) columns was experimentally investigated to enhance this advantage. 20 HSS-CFST columns, five normal-strength steel spiral-confined CFST (NSS-CFST) columns, and four CFST columns without an internal steel spiral were tested under axial compression. It was found that the high strength characteristic of the internal HSS spiral was fully utilized, thereby alleviating the non-uniform confinement of the square steel tube and significantly enhancing the ductility and strength of CFST columns. The ultimate strength improvement induced by increasing the volume of HSS spiral is more pronounced than that caused by increasing the same volume in the outer steel tube. A strong interaction exists between the confinement contribution made by the internal steel spiral and that provided by the outer steel tube. A new ultimate axial load model was subsequently proposed based on the experimental findings of the author's own and those collected from the literature, which significantly extends the range of the parameter space and clearly illustrates the interaction between the steel tube and internal steel spiral.
... However, the former ones are mostly preferred in designing composite columns attributing to their ease of connection to the steel beams. Besides, in some studies [4][5][6][7], stiffening methods/schemes have been used for enhancing the confining pressure of rectangular sections, as shown in Figure 1. Moreover, CFDST members with octagonal sections can suit the architectural and functional requirements of CFDST members because they provide greater confinement than that induced by the rectangular sections and ease of connection to the steel beam compared to circular sections. ...
... Surface-to-surface interaction is utilized to model the interaction between the metal and concrete in this study [1,5,17]. Hard contact condition was specified to simulate the behavior in the normal direction designated by avoiding the surface penetration in compression and allowing the separation in tension [33,34], while the Coulomb friction model with penalty friction and directionality of isotropic was adopted to simulate the interface in the tangential direction. ...
... For the longitudinal stiffeners, these components were merged with the steel tubes in a single part, hence the interaction between the steel tubes and stiffeners was considered by the inherent way of sharing common nodes. Although the longitudinal stiffeners were merged with the steel tubes, they were embedded into the sandwiched concrete [5,33]. Since the Figure 3. ...
Octagonal concrete-filled double-skin steel tube (OCFDST) columns have drawn the attention of
academia and building industries since they combined the advances of higher confinement of circular
CFDST columns and the better constructability options of square CFDST columns. Therefore, this
paper investigates numerically the behavior of axially compressed OCFDST stub columns by the
means of finite element analysis employing ABAQUS software. The accuracy of the developed finite
element (FE) models was validated against th e experimental results in terms of axial load-axial
shortening curves and the ultimate strength of the test specimens. Then, subsequent parametric studies
considering a wide range of outer parameters were performed by the verified FE model on the effects
of various parameters including the thickness of outer steel tube (to), the thickness of inner steel tube
(ti), the diameter of inner steel tube (Di) and type and arrangement of stiffening schemes. The
numerically generated data were then used to evaluate the applicability of the design guidelines
provided by existing European, North American, and Chinese provisions for composite columns.
Based on the results, it was found that EC4 and modified EC4 formulas can safely be adopted to predict
the design ultimate strength of OCFDST stub columns. AISC360 can also give a reasonable for
non-stiffened specimens while, DBJ provides un-conservative predictions of ultimate strength when
applied to non-stiffened OCFDST stub columns, while it can accurately calculate the ultimate strength
of the OCFDST axial members with different stiffening schemes
... Square steel tubes are widely used in engineering construction owing to their large section inertia and convenient connection with beams [16,17]. Yuan et al. [18] investigated the mechanical properties of square CFST columns under axial compression through experiments and numerical simulations. Hu et al. [19] conducted numerous experiments and analyses on the axial compression performance of square CFST columns and proposed various design suggestions considering the load capacity of square CFST columns under axial compression. ...
This paper presents an experimental study on the axial performance of square/rectangular concrete-filled steel tubular (CFST) columns. A total of 34 specimens, classified as four groups, were fabricated and tested under uniaxial compression. The failure modes, axial stress–strain curves, ultimate axial stress, and ductility were analysed in detail considering the effect of the steel ratio, steel fibre addition, concrete type, cross-section type, and size of the specimens. Further, the confinement index (ξ) and strength index (SI) was discussed. The obtained findings revealed that the ultimate axial stress of CFST columns was increased by increasing the thickness of the steel tube and adding steel fibres to the concrete mixture. When the steel ratio, steel tube thickness, and specimen height were the same, the type of cross-section (the square and the rectangular section) exhibited an insignificant effect on the axial stress–strain of the CFST column. Finally, a formula was proposed to estimate the ultimate axial stress of both square and rectangular CFST columns, with the concrete core strength ranging from 70 MPa to 150 MPa.
... Extensive experimental investigations have been undertaken to determine the behavior of CFST circular and rectangular columns (Ci et al., 2021;Fujimoto et al., 2004;Giakoumelis and Lam 2004;Huang et al., 2019;Han 2002;Lee et al., 2011;Sakino et al., 2004;Uy 2001;Yuan et al., 2019;). It has been well understood that the circular cross section provides significant confinement on the filled concrete, which improves both the concrete strength and ductility, whereas the confinement induced by the rectangular or square tube is minor but the ductility of the encased concrete is shown to improve considerably (Sakino et al., 2004). ...
Hexagonal concrete-filled steel tubular (HCFST) columns have been used to carry large loads in tall composite buildings. Their behavior and strength are different from those of circular and square concrete-filled steel tubular (CFST) columns due to the confinement effect. This article describes a computational modeling method of nonlinear fiber analysis recognizing the concrete confinement for the response simulation of HCFST short columns subjected to axial compression. New constitutive relations of confinement for quantifying the confining stresses on the concrete confined by the hexagonal steel tube and the residual concrete strength are developed by means of analyzing existing test data. The computational modeling program written is verified by existing experimental data and then employed to ascertain the behavior of HCFST columns with important parameters. The current design standards for CFST circular columns are used to determine the strengths of HCFST columns to evaluate their applicability to the design of HCFST columns. Proposed is a new simple design equation for computing the axial capacities of HCFST columns. The computational model and the design equation proposed are shown to be accurate, and effective simulation and design tools for HCSFT stub columns that are loaded concentrically in comparisons with the current design codes.
... Because of their higher bearing capacity, ductility, and ease of connection to the beams, square concrete-filled steel tubular (CFST) columns are widely used in the construction of composite structures (Wang et al., 2018;Yuan et al., 2019;Zhu et al. 2019). The square CFST columns are often made of thin-walled steel tubes that are particularly susceptible to the localized buckling which affects their structural performance significantly. ...
In this paper, the structural behavior of concrete-filled double steel tubular (CFDST) stub columns composed of square hollow sections is investigated experimentally and numerically. The experimental program comprises compression tests on short columns loaded concentrically. The test parameters mainly focused on the influences of the width-to-thickness ratios of steel tubes and concrete strength on the axial behavior of CFDST stub columns. Finite element (FE) models are also developed to investigate the influences of a wide range of structural parameters on their axial performance. It is observed that square CFDST columns have improved strength and ductility compared to their CFST and DCFST counterparts. Finally, a calculation formula is proposed to predict their ultimate compressive strengths under the axial compression load.
... Extensive experimental and numerical researches on the failure behavior of CFST columns under axial compression [2][3][4][5][6], eccentric compression [7][8][9] and flexure [10] have been conducted, however the shear behavior of CFST columns was only addressed in extremely limited literatures [11][12][13][14][15]. Tomii and Sakino [11] put forward a series of experiments on shear behavior of square CFST columns with sectional width of 100 mm subjected to constant axial compression and shearing force. Results show that the shear failure dominates when shear-span ratio ranges from 0.83 to 1.0, while the bending failure dominates when shear-span ratio ranges from 2.0 to 3.0. ...
Concrete-filled steel tubular (CFST) short columns under the action of wind and seismic load often endure high shearing force and show brittle shear failure, which may exhibit obvious size effect. In this study, a three-dimensional meso-scale simulation method that can consider both the concrete heterogeneity and the contact behavior between concrete core and steel tube was established to investigate the failure behavior and size effect of square CFST columns under combined lateral and axial loads. After verification of the meso-scale model, simulation tests were carried out to discuss the influence of shear-span ratio, axial compression ratio and steel ratio on the failure modes, the nominal shear strength, the ductility and the size effect of square CFST columns. Results indicate that, when the shear-span ratio increases from 1.0 to 3.0, the failure mode of CFST columns turns from brittle shear failure to ductile bending failure, the nominal shear strength decreases and ductility increases, and the size effect in shear would be weakened. The nominal shear strength increases and the column shows better ductility with the increasing axial compression ratio less than 0.4, while the nominal shear strength decreases and the columns present obvious brittleness with the increase of axial load larger than 0.4. Moreover, as steel ratio increases from 0.05 to 0.15, the nominal shear strength and ductility of CFST columns increase, and the size effect on nominal shear strength cannot be weakened. At last, a theoretical formula that can quantitatively show the influence of shear-span ratio on size effect in shear strength was proposed to predict the shear capacity of square CFST columns. The available test data and the simulation results illustrate the rationality and applicability of the theoretical formula.
... According to the different section shapes, CFST columns can be generally divided into circular, square, T-shaped, cross shaped and L-shaped CFST columns. Although the researches show that the effect of confinement on circular CFST (C-CFST) columns is better than that of the squared CFST (S-CFST) [3], S-CFST columns have the advantages of higher bending rigidity and simpler beam-column joints in practical engineering [4]. ...
... The results proved that the corrosion would lead to a significant reduction in the ultimate strength of the CFST stub columns. Han and his research team [4,[13][14][15][16][17] conducted test research and theoretical analysis on the performance degradation of the CFST columns under sustained load and chloride corrosion, specifically including tension, compression and bending, and finally proposed simplified calculation formulas. Zhang [18] carried out axial static load test on thin-walled C-CFST columns being in corrosive environment. ...
The axial performance degradation of 40 concrete-filled squared thin-walled steel tubular stub columns in severe cold and acid rain area were studied in this paper. The test parameters include freeze-thaw cycles (0, 80, 160 and 240), corrosion rate (0, 10%, 20% and 30%) and wall thickness (3.0mm and 4.5mm). The test process involves three parts: only acid rain corrosion test, only freeze-thaw cycle test and alternation test of acid rain corrosion and freeze-thaw cycle. The results reflect that the failure modes of the specimens were the local buckling of the steel tube and the transverse tensile fracture at the corner of steel tube. Derived from the test results, the development of the rigidity, ductility and strength reduction factor of concrete-filled squared thin-walled steel tube with the different parameters were discussed, as well as the lateral deformation coefficient of the steel tube and the confinement effect of the core concrete. After validating the design methods in different standards, the modified Chinese standard prediction formula was recommended to evaluate the ultimate strength of concrete-filled squared thin-walled steel tube stub columns under the alternating action of acid rain corrosion and freeze-thaw cycle.
