L-shaped Concrete-filled Steel Tubular Columns Research Articles

Design of improved multi-cell L-shaped CFST columns under compression and bending

In recent years, there has been a notable surge in proposals for various forms of special-shaped concrete-filled steel tubular (CFST) columns. Despite various methods developed by researchers for determining the bearing capacity of multi-cell special-shaped CFST columns under different loading conditions, these methods remain lack unified. In this study, FE models were developed to simulate performances of improved multi-cell L-shaped CFST (ML-CFST) column under compression and bending. Parametric analyses have been performed to evaluate impact of various factors, including steel yield strength fy, compressive strength of concrete fcu, steel thickness t, loading direction θ, web height c, and axial load ratio n, on performances of ML-CFST columns. The findings of study indicate that the unidirectional flexural capacity of ML-CFST member exhibits a nearly linear relationship with the variables of t, fy, and c, with a minimal impact observed from fcu on flexural capacity. The width of extended section b, fcu, fy, and t have a certain effect on flexural capacity at any angle, particularly fy, t, and b. While fcu, fy, and t exert some influence on N/Nu-M/Mu correlation curves, their influences are marginal compared to the loading direction, which is the predominant influencing factor. Additionally, Mx0/Mπ/4-My0/M3π/4 curves gradually protrude outward with the increase in n. The effects of t, fy, and fcu on the shape of Mx0/Mπ/4-My0/M3π/4 curve were relatively insignificant. Simplified unidirectional flexural capacity calculation models were proposed based on stress analysis of cross-section under ultimate states. Given that flexural capacities estimated by simplified calculation model are slightly conservative, it is recommended to increase the flexural capacities by 10 %. Furthermore, an elliptical equation was formulated to predict the flexural capacity at any angle, with the predictions being slightly conservative. Based on ultimate equilibrium theory, a simplified calculation method was presented to predict unidirectional eccentric bearing capacities of ML-CFST columns. Through regression analysis, a simplified calculation method expressed as polar coordinate form for biaxial eccentric bearing capacity was established, with calculated values aligning well with FE results.

Experimental Study on L-shaped Concrete-filled Steel Tubular Columns under Axial Compression and Eccentric Compression

Experimental Study on L-shaped Concrete-filled Steel Tubular Columns under Axial Compression and Eccentric Compression

Finite Element Analysis of Axial Compression Behavior of L-Shaped Concrete-Filled Steel Tubular Columns with Different Combinations

L-shaped concrete-filled steel tubular (CFST) columns, a kind of structural member appropriate for high-rise buildings, not only avoid the defect of conventional square columns protruding from the wall but also have the green and low-carbon properties of steel structures appropriate for fabricated construction. To learn more about their axial compression behavior, refined 3D finite element models were established using the general finite element software ABAQUS. The reliability of the models was subsequently verified based on failure tests and load–displacement relation tests on eight L-shaped specimens. The axial compression mechanism of L-shaped CFST columns was investigated using the verified finite element models. Further systematic parameter analysis was carried out to investigate the influence of parameters such as steel strength, concrete strength, length ratio of long limb to short limb, the angle between the two limbs, and combination methods on the axial compression behavior of L-shaped CFST columns. The results demonstrate that the angle between the two limbs has a significant impact on the stress distribution of concrete and steel pipes. The corner effect increases as the angle between the two limbs decreases. The combination of F-type specimens can better exert the constraint effect of steel pipes on concrete, while the triangular cavity of unequal-limb specimens and specimens with an included angle of 60° cannot effectively trigger the interaction between steel pipes and concrete. The initial stiffness of L-shaped CFST columns increases with an increase in concrete strength and a decrease in limb length ratio, which is not sensitive to changes in steel strength and the included angle. The peak bearing capacity of the specimens increases with increases in steel strength and concrete strength and a decrease in the limb length ratio. Compared to C-type and Z-type specimens, the initial stiffness of F-type specimens is slightly higher, and the peak bearing capacity is significantly increased.

Experimental Study on the Seismic Performance of L-Shaped CFST Columns in Different Combinations

L-shaped concrete-filled steel tubular (CFST) columns represent a valuable structural element with an L-shaped cross-section, primarily employed in the corner columns of framed structures. These columns offer several advantages, including space efficiency by avoiding column protrusion, robust mechanical properties, high load-bearing capacity, ductility, and efficient utilization of internal building space. This article presents the outcomes of an experimental investigation into the seismic behavior of L-shaped CFST columns. The experimental study investigated the seismic performance of nine L-shaped CFST columns while considering different cross-sectional dimensions, their combinations, and varying levels of confinement. The results obtained from this study indicate that L-shaped CFST columns possess favorable seismic performance characteristics. However, there exists the potential for significant improvement by modifying certain parameters. Enhancements in seismic performance were observed when increasing the cross-sectional dimensions of the column and the length of its legs. The use of steel tubes and the provision of adequate confinement also demonstrated notable benefits. Moreover, the better arrangement of steel tubes within the column positively influenced seismic performance. These findings can potentially inform and enhance the design of L-shaped CFST columns, rendering them more resilient to seismic forces.

Experimental research on fire behavior of L-shaped CFST columns under axial compression

Six L-shaped concrete-filled steel tubular (LCFST) stubs were designed and tested under the axial compression and ISO-834 standard for fire. The temperature distribution, axial deformation development, fire resistance, and failure modes of LCFST columns under fire were investigated. The fire test results show that the fire resistance of the specimen decreases with the increasing axial compression ratio and increases linearly with the thickness of the fire protection layer; and the tension-bar stiffened column has slightly higher fire resistance than multi-cell columns. The fire behavior of LCFST columns was then analyzed using the finite element program ABAQUS and the simulated temperature distributions and fire resistances were found to be in good agreement with the test results. Moreover, the LCFT column has slightly higher fire resistance than the square CFST column specified in the design code GB50936–2014. The parametric analysis results show that slenderness ratio, column limb thickness, eccentricity ratio, and fire protection layer thickness all affect the fire resistance of LCFST columns. It was discovered that the first level fire-resistance rating of LCFST columns could be achieved by adopting a reasonably thick fire protection layer. Lastly, simplified formulas for the fire resistance and fire protection layer are proposed, which can reduce the fire protection layer thickness by 50% compared to the current fire design requirements for CFST columns.

Behavior of stiffened and multi-cell L-shaped CFST columns under eccentric compression

The mechanical behavior of the traditional special-shaped concrete-filled steel tubular (CFST) columns can be improved by employing longitudinal stiffeners or using multi-cell cross-section. In practical application, the stiffened and multi-cell L-shaped CFSTs are often subjected to bi-directional loading. However, there are only few research studies on their performance as loaded eccentrically with different orientations of the loading and there is no relevant design guideline. This paper reports tests on 16 L-shaped CFST columns (nine stiffened, six multi-cell specimens and one reference specimen) loaded in eccentric compression. The main variables were the angle indicating the orientation of the load action line (0°, 45°, 135°, 180° and 225°), load eccentricity ratio (0, 0.25 and 0.5) and slenderness ratio (31.5 and 41.9). Finite element models for the eccentrically loaded stiffened and multi-cell L-shaped CFST columns were developed. Based on the parametric analysis, practical design methods were proposed for predicting the bearing capacity based on the stability loss and the axial force vs. bending moment interaction diagrams for the members considering the influence of the load orientation at the end face of the column.

Experimental and numerical study of fire performance of L-shaped concrete-filled steel tubular columns under eccentric compression

Six special-shaped columns composed of concrete-filled steel tubes (CFST) were designed and tested based on the ISO-834 temperature curve to access their fire performance under eccentric loads. Key test variables include the types of stiffener, load eccentricity, as well as load angle, and the failure modes, temperature distribution, and deformation of specimens were analyzed. The test outcomes indicate that the L-shaped CFST columns’ fire resistance declines as the load eccentricity rises, but its decrease amplitude narrows under a relatively high eccentricity. Besides, the impact exerted by the load angle on the columns’ fire resistance is also significant. A Finite Element Analysis (FEA) method was carried out afterward and compared with the test outcomes. Moreover, an extensive parametric analysis containing 2008 FEA models was developed to study the impact of major parameters on the L-shaped CFST columns’ fire resistance, namely load ratio (n), slenderness ratio (λ), column limb width (B), column limb depth-to-width ratio (D/B), load eccentricity ratio (e/r0), steel ratio (αs), steel strength (fy), concrete strength (fck), and load angle (θ). The analysis results imply that the parameter of load ratio (n) remarkably affects the columns’ fire resistance, while the other parameters exert a certain impact on the fire resistance when n < 0.5. Given the test and analysis, a simplified calculation approach for the fire resistance of L-shaped CFST columns is designed.

Performance of composite L-shaped CFST columns with inner I-shaped steel under axial compression

To improve the behaviour of conventional L-shaped concrete-filled steel tubular (CFST) columns, experiments and numerical modelling of composite L-shaped CFST columns with inner I-shaped steel under axial compression were conducted. Experiments of thirty-two specimens, including 16 short columns and 16 middle long columns, were carried out with various steel tube confinement index (θ), built-in steel ratio (ρ) and slenderness ratio (λ). The load-average longitudinal strain curves, load-deflection curves and bearing capacity of the specimens were also investigated. The experimental results demonstrate that those specimens with higher values of θ and ρ, and lower value of λ, have higher ultimate bearing capacity. When the height of column remains constant, the strength and ductility can be improved by increasing θ and ρ. With the increase of λ, the local buckling failure is gradually transformed into a combination of local buckling and global buckling. A finite element analysis (FEA) model was developed to investigate the performance of composite L-shaped CFST columns with inner I-shaped steel under axial compression, and the feasibility of the FEA model was verified by the comparison against experiment results. Finally, the formulas were also proposed to estimate the ultimate bearing capacity of short and middle long composite columns and the estimated results match well with the experimental results.

Hysteretic behavior of multi-cell L-shaped concrete-filled steel tubular columns at different loading angles

Multi-cell L-shaped concrete-filled steel tubular (CFST) columns have the advantages of avoiding column protrusion, saving room space and good mechanical behavior. They can be used as the corner columns in building structures. In practical engineering, the columns may be subjected to earthquake action from different directions. However, there are few experimental and numerical studies on this kind of columns at different loading angles. This paper presents four tests carried out on multi-cell L-shaped CFST columns subjected to combined constant compression and lateral cyclic loads. The main variables were loading angles (0°, 45° and 135°) and axial load levels (0.25 and 0.5). The failure modes, lateral load – displacement hysteretic curves, envelope curves, stiffness degradation, ductility, energy dissipation, deformation and moment – curvature curves were obtained. A finite element model was developed to simulate the multi-cell L-shaped CFST columns at different loading angles, and the predicted results agreed well with the test results. Moreover, the parametric analysis was conducted to investigate the effects of various parameters on lateral load – displacement curves of the columns under diagonal loading.

Experimental study on hysteretic model for L-shaped concrete-filled steel tubular column subjected to cyclic loading

L-shaped concrete-filled steel tubular (L-CFST) column can improve the space layout and can increase the utilization rate of the indoor space. It is a new type of structural column in civil engineering. At present, the research on seismic performance of L-CFST column is insufficient. In this paper, nine L-shaped concrete-filled steel tubular columns were subjected to cyclic loading to study the seismic performance, such as the hysteretic behavior, bearing capacity and stiffness. In the test, three parameters (slender ratio, axial compression ratio and steel ratio) were considered. Simultaneously, the regression analysis of the test results is carried out to establish the hysteretic model of the L-CFST column, and the authors proposed the calculation formulas on the model curve based on the parameters, i.e. load, displacement and stiffness degradation. The results of the hysteretic model of L-CFST columns are in good agreement with the experimental results, which provides a theoretical basis for the analysis of the non-linear seismic behavior of L-CFST columns.

Seismic Damage Investigation of Spatial Frames with Steel Beams Connected to L-Shaped Concrete-Filled Steel Tubular (CFST) Columns

Currently, the frame structures with special-shaped concrete-filled steel tubular columns have been widely used in super high-rise buildings. Those structural members can be used to improve architectural space. To investigate the seismic behavior of spatial composite frames that were constructed by connecting steel beams to L-shaped concrete-filled steel tubular (CFST) columns, a finite element analysis (FEA) model using commercial finite element software ABAQUS was proposed to simulate the behavior of the composite spatial frames under a static axial load on columns and a fully-reversed lateral cyclic load applied to frames in this paper. Several nonlinear factors, including geometry and material properties, were taken into account in this FEA model. Four spatial specimens were designed, and the corresponding experiments were conducted to verify the proposed FEA model. Each testing specimen was two-story structure consisting of eight single span steel beams and four L-shaped CFST columns. The test results showed that the proposed FEA model in this paper could evaluate the behavior of the composite spatial frames accurately. Based on the results of the nonlinear analysis, the stress developing progress of columns is investigated. The load transferring mechanism and failure mechanism are also determined. The results are discussed and conclusions about the behavior of those spatial frame structures are presented.

Axial load behavior of L-shaped CFT stub columns with binding bars

This paper is concerned with the axial load behavior of L-shaped concrete-filled steel tubular (CFT) stub columns with binding bars provided to improve the mechanical behavior of these elements. Six specimens with binding bars and one specimen without binding bars were tested to examine the effects of horizontal spacings and diameters of binding bars, and width-to-thickness ratios of steel plates on the failure modes, maximum strength, and ductility of L-shaped CFT stub columns. Experimental results demonstrate that the local buckling of the steel tube can be delayed by setting binding bars, the confinement effects on the core concrete can be improved significantly, and the bearing capacity and ductility of the L-shaped CFT stub columns are enhanced by 7% and 26%, respectively. Based on a constitutive model of confined concrete, a method for calculating the maximum strength of L-shaped CFT columns with and without binding bars is proposed. The method is verified with experimental results from this test program and data from other experiments. The results predicted by the proposed method show better agreement with the experimental values than the values predicted by AISC (2005), BS5400 (2005), EC4 (2004) and GJB (2001).

Study on Mechanism of L-Shaped Concrete-Filled Steel Tubular Columns Subjected to Axial Compression

In this paper, a constitutive relationship of the concrete core restrained by L-Shaped steel tube is put forward based on referring to the constitutive relations of core concrete in concrete-filled square steel tube columns, which takes the restraint of steel tube to concrete as an equivalent confinable effect coefficient . Load-deformation relationship of L-Shaped concrete-filled steel tubular column subjected to axial compression is analyzed by finite element analysis (using ABAQUS software). The predicted load versus deformation relationship cures are in good agreement with those of tests based on the finite element analysis, loads carried by steel tubes and concrete respectively during the loading process, as well as interactions between them are analyzed. Finally, influences of length-width ratio and width-thickness ratio on the interaction between steel tubes and concrete are investigated.