L-shaped Concrete-filled Steel Research Articles

Experimental and numerical analysis of L-shaped concrete-filled steel tube stub columns

This paper reports experimental and numerical studies on the cross-sectional compression resistance and behaviour of a novel L-shaped concrete-filled steel tube system. The novel composite system is proposed to eliminate concave corners and enhance the confinement of the outer steel tube to the concrete infill. A testing programme was firstly conducted, including nine tensile steel coupon tests, six compressive concrete cube tests and ten stub column tests. Upon testing, all the ten L-shaped concrete-filled steel tube stub column specimens were found to fail by local buckling. Finite-element models were then developed in the finite-element analysis software ABAQUS and validated against test results. The validated models were then employed to perform parametric studies to obtain an additional set of 48 numerical data. Test and numerical results were used to perform a design analysis, in which the suitability of the design rules in the European code EN 1994–1-1, the American specification ANSI/AISC 360 and the Chinese code GB 50936 for the developed L-shaped concrete-filled steel tube stub column system was assessed. The analysis results reveal that both EN 1994–1-1 and GB 50936 yield unsafe compression resistance predictions for the studied L-shaped concrete-filled steel tube stub columns, owing to the improper consideration of the contributions of the outer steel tube and the concrete infill to the overall capacity, while ANSI/AISC 360 offers safe design with high accuracy. The research findings are expected to contribute to the safe and wide use of the proposed novel L-shaped concrete-filled steel tube system in structural engineering and also to the further development of the current international design standards.

Combined axial load-biaxial bending interaction method for L-shaped CFSP shear walls

This paper reports the development of axial load and biaxial bending interaction method for L-shaped concrete-filled steel plate (CFSP) composite shear walls based on fiber section analysis model using the uniaxial constitutive relationship of materials. Owing to the complex interaction between the two perpendicular wall limbs (web and flange) of an L-shaped shear wall, the contour shape of the My-Mz curve is asymmetric. Linear transformation was employed to reduce the asymmetry of the contour shape, eliminate the influence of dimension, and perform parametric analysis. The analysis results indicate that when 0° ≤ θ(neutral axis angle) ≤ 90°, the influence of width-to-thickness ratio (hw1/bw) and shape coefficient (γ) on the coefficient that controls the contour shape (α) was negligible. The effect of shape coefficient (γ), steel content ratio (ρ), compressive strength of unconfined concrete (fc0), and yield strength of steel plate (fyp) on α is not significant for −180° ≤ θ ≤ −90°. Further, simplified equations were suggested to determine α. The axial load-moment interaction curve expressions for distinctive loading directions were determined by establishing the calculation method for the curve's characteristic points (axial load capacity, bending capacity, boundary points). Subsequently, the characteristic points were combined with the contour shape of the axial load-moment interaction curve derived by fitting the finite element simulation data to generate the axial load-moment interaction curve equations. A design approach was finally formulated based on the equations for the biaxial moment capacity curve and the axial load-moment interaction curves of the characteristic loading directions.

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 and numerical study of resistance of multi-cell L-shaped concrete-filled steel tubular stub columns under biaxial eccentric compressive loading

This study aims to understand the cross-sectional resistance and develop practical resistance equations for multi-cell L-shaped concrete-filled steel tubular (ML-CFST) stub columns under biaxial eccentric compressive loading based on experimental testing and numerical analysis. Eighteen specimens were firstly tested to investigate experimentally their failure modes, nonlinear structural behavior, and the influence of different loading angles (θ) and eccentricities on the load-carrying capacity. Secondly, detailed nonlinear finite element models were developed and validated against test results, and further used for parametric analysis to explore untested scenarios. This facilitated the construction of a failure surface, which was interpreted as a family of Mx-My interaction curves under a variety of axial compression ratios (n), where Mx and My are the bending moments about the minor and major axes, respectively. Results showed that ML-CFST specimens exhibited favorable structural performance, and n and θ had a considerable influence on the normalized Mx-My interaction curves, compared to other geometric and material strength parameters (i.e., depth-to-width ratio of section limb, steel-to-concrete area ratio, steel yield strength and concrete compressive strength) studied. To facilitate engineering use, a dimensionless interaction equation for normalized Mx-My was developed in good agreement with experimental results.

Uniaxial Eccentric Load Behavior of L-CFSST Composite Column

This study presents the mechanical behavior of L-shaped concrete-filled square steel tube (L-CFSST) composite columns under uniaxial eccentric compression. Nine specimens were tested and the effects of eccentricity, steel tube thickness, steel yield strength, and slenderness ratio were investigated regarding failure modes, ultimate load, load-lateral displacement curves, and load-strain curves. Test results showed that, under uniaxial eccentric load, these columns showed favorable mechanical properties and steel tubes showed strong cooperative working performance. There were two types of failure modes for these columns: local buckling of the steel tube or overall bending of the specimen. ABAQUS was used to simulate the loading process and the accuracy of the numerical simulation results was verified by comparing failure characteristics, load-displacement curves, and ultimate bearing capacity with the test results. The N/Nu-M/Mu curves of the columns under uniaxial eccentric load with different parameters were simulated by the finite element method. A simplified formula for predicting the N/Nu-M/Mu relationship was established based on the finite element analysis results, which might be a workable approach for designing L-CFSST composite columns in engineering practice.

Experimental and numerical study on seismic performance of square and l-shaped Concrete-filled steel tubes column Frame-Buckling steel plate shear walls

To boost the application of concrete-filled steel tubes (CFTs) in high-rise buildings, square and l-shaped CFT are used as boundary columns in frame-buckling steel plate shear walls (SPSWs). This study presents an eco-friendly and sustainable solution for using tailings and recycled aggregate concrete as the infill concrete in CFT columns. Cyclic quasi-static tests are performed on two one-span, two-story specimens. A four-corner gusset connection connects the shear wall to the boundary columns. Subsequently, the failure modes, hysteretic curves, and characteristic capacities are analyzed. The failure and hysteretic behaviors of the two tested specimens are simulated using the finite element (FE) software ABAQUS and verified against the experimental results. Based on validated models, parametric studies are established and analyzed. The results imply that the frame-buckling SPSW exhibits good seismic performance. The failure modes of the two specimens are similar; however, the specimen using the l-shaped column exhibits more excessive deformation. In addition, the use of an l-shaped column increases the bearing capacity and ductility by approximately 10 %; simultaneously, the stiffness increases by 30 %. The buckling of the steel plates primarily consumes seismic energy. The results of this study can be used as a reference for engineering practice.

Experimental study on multi-cellular L-shaped CFST slender columns under biaxial eccentric compression

Multi-cellular L-shaped concrete-filled steel tubular (MCL-CFST) column is an improved L-shaped CFST column, which is composed of multiple rectangular steel tubes welded by U-shaped steel plates and then filled with concrete. The global stability capacity of MCL-CFST slender columns is vital for engineering applications. However, few investigations have been carried out on the stability performance of the MCL-CFST slender columns. This paper mainly focuses on the global stability performance of MCL-CFST slender columns. Firstly, six hinged supported MCL-CFST slender columns were designed and tested under biaxial eccentric loading. The load-displacement curves, failure modes, strain development and second-order effects of MCL-CFST slender columns were reported. Then, a refined finite element (FE) model of the MCL-CFSTs was established and verified by experimental results. Moreover, based on the validated FE model, the effects of eccentricity, column height and sectional dimension on the stability performance of MCL-CFSTs under eccentric loading were investigated, and the bending resistance curves Mx/Mxu-My/Myu in two directions under various parameters were obtained. These results can provide valuable references for engineering practice.

Seismic research on column base joint of L-shaped CFST columns under cyclic loading

The newly exposed column base (ECB) for L-shaped concrete-filled steel tube (CFST) columns investigated in this study consists of an outer base plate, a concrete cushion, and anchor bolts. Three ECB specimens of the L-shaped CFST column were tested under constant axial loading and cyclic horizontal loading to investigate their seismic behavior. The failure mode, moment versus rotation relationship, hysteretic behavior, and ultimate moment strength were analyzed. The test results indicated that the failure mode of ECB is the failure of the concrete cushion and yielding of the base plate and anchor bolts. Furthermore, a parametric analysis based on a verified finite element model was performed to investigate the influence of various parameters on the ultimate moment strength. Finally, a simplified strength model of ECB for L-shaped CFST based on the composite yielding method was proposed.

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.

Seismic performance of joint between L-shaped CFST column and H-section beam with lower plate and extended flange plate

Bolted joints are widely used in beam-to-column joints in structures due to the advantages of fast construction, convenient installation and disassembly, and resource conservation. A bolted joint configuration between L-shaped concrete-filled steel tubular column and H-section beam with lower plate and extended flange plate was proposed, realizing fully-bolted connections between the upper and lower columns, as well as between the beam and the column. Four specimens, with different bolt numbers on the beam flange or different configurations of stiffeners, had been designed and tested under cyclic loads. Finite element models were developed and validated based on the test results, and parametric analysis was performed to analyze the influence of extended flange plate thickness on the mechanical properties of the joints. According to the results, the hysteresis curves of the specimens were plump, and the slippages between the extended flange plate and the beam flange improved the ductility and energy dissipation capacity of the specimens. Increasing bolt number on the beam flange significantly increased the joint resistance and stiffness. The beam vertical stiffeners limited the development of the plastic deformation of the beam flange, thereby reducing the local buckling of the beam section. Based on the experimental and finite element analysis results, simplified calculation formulas and design procedures for the joint are proposed.

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.

Flexural Strength Evaluation of Multi-Cell Composite L-Shaped Concrete-Filled Steel Tubular Beams

Concrete-filled steel tubular (CFST) members have been widely used in industrial structures and high-rise residential buildings. The multi-cell composite L-shaped concrete-filled steel tubular (ML-CFST) cross-section, as an innovative, special-shaped structural arrangement, may solve the issue of normal CFST members protruding from walls and result in more usable interior space. Currently, no design rules are available for the application of ML-CFST members. One of the primary objectives of the present study is to develop recommendations in line with the unified theory to evaluate the bending moment resistance of ML-CFST beams. According to the unified theory, the bending moment resistance of an ML-CFST beam is related to the compressive strength (fsc) and the flexural strength index (γm) of a composite section, in which the accuracy of γm and fsc are affected by a confinement effect factor (ξ). Nevertheless, the original expression of ξ is not suitable for ML-CFST sections, since the appreciable effect of the irregular shape on confinement is neglected. Considering the cross-sectional geometry and boundary conditions of the cells, an equivalent shape factor to modify the confinement effect was proposed in this study through dividing the infill concrete into highly confined areas and less confined areas. An adequate formula to calculate the fsc and an approximate expression of γm for the ML-CFST sections was then developed. Furthermore, four-point bending tests on eight specimens were carried out to investigate the flexural performance of the ML-CFST beams. Lastly, the proposed formulas were assessed against experimental and numerical results. The comparisons show that the proposed unified theory-based approach produced accurate and generally conservative results for the ML-CFST beams studied.

Flexural behaviour of stiffened and multi-cell L-shaped CFSTs considering different loading angles

Stiffened and multi-cell L-shaped concrete-filled steel tubular (CFST) members are often subjected to the loads from different loading angles as corner columns. Moreover, the flexural behaviour is the basis for the research of beam-columns and the determination of axial force-bending moment interaction curves. However, little work has been done on the flexural behaviour of these kinds of members at different loading angles. In this study, a total of 11 L-shaped CFST specimens with the variables of sectional type and loading angle were tested under pure bending. The failure mode, bending moment-deflection curves, moments-strain curves, deflection curves, flexural capacity and stiffness were investigated. It was found that the influence of loading angles is significant. The flexural capacity and stiffness of the specimens are highest at 135°, middle at 0° and 180°, and lowest at 45° and 225°. Setting longitudinal stiffeners or using multi-cell cross-section can improve the flexural capacity by about 20%. Then a finite element model was developed incorporating residual stress and cold-formed effect. Considering the effect of loading angles on the basis of the design model at 0°, the simplified formulas for flexural capacity of the stiffened and multi-cell L-shaped CFST members were proposed.

L-shaped concrete-filled steel hollow-section columns under diagonal cyclic loading

L-shaped concrete-filled steel hollow-section (CFSHS) columns have the potential to be widely used as corner columns, and have the advantage of creating larger usable areas in buildings. However, few experimental tests of this kind of column under diagonal cyclic loading have been reported. Tests on eight L-shaped CFSHS columns with equal legs were conducted to study their hysteretic behaviour; the test variables were: loading angle, concrete compressive strength, axial load level and presence or absence of stiffeners. The failure process and modes, stiffness degradation, ductility and energy dissipation were observed, and lateral load–displacement hysteretic curves and envelope curves were plotted. The results show that L-shaped CFSHS columns have generally good hysteretic behaviour and that the displacement ductility coefficients are in excess of 3 in most cases. Columns with a loading angle of 45° have &gt;10% decrease in ultimate strength but a slightly higher ductility than columns with a loading angle of 0°. The ultimate strength, ductility and energy dissipation of columns all decrease with increasing axial load levels. Discontinuously welded stiffeners can improve the ultimate strength and ductility, but the amplitude is limited. Finally, a finite-element model was developed; the predicted results agree well with the test results.

Experimental study on the seismic behavior of prefabricated L-shaped concrete-filled steel tube with rectangular multi-cell columns under different lateral loading directions

Prefabricated residential buildings are becoming the focus of the construction industry. Simultaneously, in order to improve the seismic behavior of traditional RC special-shaped columns, a prefabricated special-shaped concrete-filled steel tube with rectangular multi-cell (S-CFST-R) column was proposed for residential systems. The seismic test of prefabricated L-shaped concrete-filled steel tube with rectangular multi-cell (L-CFST-R) columns was conducted in this study. Three full-scale L-shaped specimens with high practical guidance were designed which were based on the common parameters of residential buildings. A quasi-static test method under a low cycle load was used to simulate the earthquake action. Taking different loading directions (0°, + 45°, and + 135°) as the main research factors, the failure state, bearing capacity, hysteretic behavior, ductility, energy dissipation capacity, strength degradation, stiffness degradation, and strain change of each specimen were studied and analyzed. Moreover, a finite element model was developed to simulate L-CFST-R columns at different loading directions, and the simulation results agreed well with the experimental results. The influence of more loading directions on the ultimate bearing capacity and skeleton curve is analyzed comprehensively. The results indicated that multi-cell special-shaped steel tubes had a strong restraining effect on the core concrete, so the L-CFST-R columns under different lateral loading directions exhibited favorable seismic behavior, which is suitable for prefabricated residential buildings.

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.