T-shaped Concrete-filled Steel Tubular Columns Research Articles

Seismic Behavior of T-Shaped Concrete-Filled Steel Tubular Column to Steel Beam Joints with Side Plates

This study investigates the seismic behavior of the T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, aimed at expanding their applicability in areas with high-seismic fortification intensity. A construction form of T-shaped CFST column to steel beam joint with side plates is presented. The variables studied in these experiments include the side plate length, the axial compression ratio, the presence of side plates, and the presence of binding bars. The force mechanism, failure modes, load–displacement curves, strength, stiffness, ductility, and energy dissipation capacity of seven specimens were evaluated under low-cycle reciprocating load. The experimental results demonstrate that the joints of side plates show a full hysteresis curve, with the ductility coefficient ranging from 1.67 to 2.49, and the equivalent viscous damping coefficient between 0.147 and 0.234. The joint panel zone displays strong deformation and energy dissipation capacity. The inclusion of side plates and binding bars improves the seismic behavior of the joint. The setting of side plates enables the formation of a plastic hinge on the steel beam, creating a beam hinge failure mechanism and satisfying the seismic design principle of “strong column and weak beam, strong joint and weak member” as required by the building structures.

Concentric and eccentric compressive behaviors of stiffened T-shaped CFST columns

Longitudinal stiffeners can improve the mechanical performance of T-shaped concrete-filled steel tubular (CFST) columns. In practical applications, stiffened T-shaped CFST is often subjected to bidirectional loading, but there has been few studies on its concentric and eccentric compressive performance considering different loading angles in the past. Therefore, six stiffened T-shaped CFST columns were tested in this paper and the main parameters were loading angle (45° and 135°), load eccentricity (0, 0.25 and 0.5), and slenderness ratio (31.5 and 41.9). Finite element (FE) models of stiffened T-shaped CFST columns under different loading angles were established, and the practical design methods for concentrically and eccentrically loaded columns were obtained on the basis of parametric analysis. The results show that the ultimate strength of stiffened T-shaped CFST column at 135° is greater than that at 45° with a difference of 12.6%. Setting longitudinal stiffeners can increase the ultimate strength by 13.2%–24.5%, and the enhancement extent declines with increasing load eccentricity. The maximum deviation of loading angles on stability coefficient under different slenderness ratios can reach 33.9%, while the corresponding deviation on relative moment (M/Mu) under different relative axial load (N/Nu) can reach 63.4%. The design method of stability coefficient for multi-cell T-shaped CFST is also available for concentrically loaded stiffened columns. Considering the loading angle transformation, the proposed interaction curve formulas can be used for the design of eccentrically loaded stiffened T-shaped CFST columns with good accuracy.

Cyclic performance of T-Shaped CFST column to steel beam joint with vertical stiffener

This paper proposes experimental and analytical research on T-shaped concrete-filled steel tubular (CFST) columns to steel beam joints in residential buildings. A novel vertical stiffener joint was advised in this paper. Six joints of 1/3 scale were performed low-cyclic loading tests, to study the seismic performance of the joints. Test parameters contain axial load ratio and vertical stiffener size. Test results indicated that the steel beam exhibited buckling failure, making all hysteretic curves present spindle-shaped. All joints demonstrated sufficient energy dissipation capacity. The peak and ultimate load decreased with increased axial load ratio. The failure mode, hysteresis curves, and skeleton curves achieved from the finite element method (FEM) are consistent with the test results. Finally, a mechanical model based on experimental and FEM results is proposed to evaluate the moment bearing capacity of the specimens.

Design of multi-cell T-shaped concrete-filled steel tubular columns under compression and bending

To date, a number of studies have been done on the calculation methods for predicting bearing capacities of multi-cell special-shaped concrete-filled steel tubular (MS-CFST) columns under axial, pure bending, and eccentric load. However, most of the existing methods only apply to a specific combination form of cross-section and have not been established in a unified formulation. In this study, finite element (FE) models were established to predict the performances of the four common combination forms of multi-cell T-shaped concrete-filled steel tubular (MT-CFST) sections subjected to axial, eccentric, and pure bending loads, and verified with the available test data. The parametric analyses were conducted to investigate the effects of steel thickness t, concrete strength fck, steel yield strength fy, aspect ratio of the web c/b, and slenderness ratio λ on the flexural and eccentric compressive performance based on the FE models. The study results demonstrated that the four common combination forms of MT-CFST sections showed the same changing trends of flexural capacity with different parameters, and the flexural capacity rose almost linearly with the increase of the parameters. The parameters (t, fy, fck, c/b, and λ) had a definite effect on the N/Nu-M/Mu correlation curve, especially c/b and λ. Furthermore, by analyzing the stress distribution of mid-span cross-section at ultimate state, the simplified calculation model for asymmetric flexural capacity applicable to different combination forms of MT-CFST section was put forward. The reduction factor of 0.9 for positive flexural capacity (WC) and the restricted width-to-thickness ratio 60235/fy are recommended. Based on the study of the constraint stress of steel tube to core concrete and the concrete constraint region distribution for the columns subjected to compression, the calculation method for predicting the axial bearing capacity applicable to different combination forms of MT-CFST section was proposed. According to the parametric analysis and shape of N/Nu-M/Mu correlation curve, the simplified method for N/Nu-M/Mu correlation curves applicable to different combination forms of MT-CFST sections was developed, which simultaneously took the influence of slenderness ratio into consideration. Besides, the calculation methods for MT-CFST members proposed in this paper have been verified with available test results and FE ones.

Seismic performance and design method of T-shaped CFST column to U-shaped steel-concrete composite beam joint with vertical stiffeners

Special-shaped concrete-filled steel tubular (CFST) columns and cold-formed U-shaped steel–concrete composite beams (CUCB) have recently been developed for efficient steel–concrete composite construction. In this study, five half-scaled T-shaped multi-cell CFST columns to CUCB joint specimens with different vertical stiffener dimensions were designed for pseudo-static test. The seismic performance of the proposed joints was analyzed based on the failure modes, hysteresis curves, ductility, and stress distribution. The experimental results show that joints with vertical stiffeners exhibit favorable seismic performance and can be considered rigid joints in a braced frame according to Eurocode 3. A finite element (FE) model for the joint was developed using ABAQUS and verified with the available experimental results. Furthermore, a parametric study was conducted to explore the effects of the vertical stiffener dimensions on joint strength and stiffness. The numerical results indicate that the vertical stiffener dimensions can significantly enhance joint strength and stiffness. A design method of such joints was proposed for practical engineering applications, including calculation formula for joint flexural capacity as well detailing for joint stiffness.

Global Stability Performance of Multi-Cellular T-Shaped CFST Slender Columns under Eccentric Compression

With the development of pre-fabricated composite structures, concrete filled steel tubular (CFST) columns have been widely used, and researches on T-shaped CFST slender columns have attracted much attention. Since ordinary T-shaped CFST columns have weak constraint on concrete at the sectional concave angle region and local buckling easily occurs in this region, a multi-cellular T-shaped concrete filled steel tubular (MCT-CFST) column was developed for improving the axial resistant performance. In this study, the global stability performance of MCT-CFST slender columns under uniaxial eccentric compression was investigated. Firstly, three pin-ended MCT-CFST slender columns were tested under eccentric compression with different eccentricities. Secondly, a refined finite-element (FE) model of MCT-CFST column was established, and the load–displacement curves, Mises stress and deformation diagrams from the FE analysis were compared with the experimental results to verify the validity of the FE model. Moreover, based on the validated FE model, a parametric analysis was carried out to study the effects of normalized slenderness ratio, thickness of steel plate and material strength on the global stability performance of MCT-CFST slender columns under combined axial and bending loads. Finally, [Formula: see text]-[Formula: see text] interaction curves were obtained from the numerical simulations, and these results were considered to provide valuable references for designing MCT-CFST slender columns in engineering practice.

Behaviors of improved multi-cell T-shaped concrete-filled steel tubular columns under eccentric loads

The improved multi-cell T-shaped CFST section is composed of four square or rectangular cavities infilled with concrete, in which the steel plates added in the section are developed as stiffeners to avoid or delay local buckling of the tube wall. In practical engineering, columns are generally subjected to eccentric load. A total of eleven multi-cell T-shaped concrete-filled steel tubular (CFST) columns were tested under eccentric loads in the symmetric axis. Effects of the web height, the slenderness ratio, the load eccentricity, and the eccentric direction of load on the mechanical behaviors of the specimens were investigated. The experimental results showed two failure modes of the specimens: before the peak load, local buckling was observed in the specimen ET-11 owing to the relatively large width-to-thickness ratio of steel plates in the web; before the peak load, slight local buckling occurred at the mid-span of the other specimens but was not observed during the test, and after the peak load, the local buckling gradually increased, which resulted from the large bending deformation. The improved multi-cell T-shaped CFST columns exhibited a better restraint effect of steel tubes on core concrete and the local buckling of steel plates was delayed or restrained. The ultimate bearing capacity of the specimen under eccentric load located on the flange (y-) was relatively larger. Furthermore, finite element (FE) models were developed to simulate the mechanical behaviors of multi-cell T-shaped CFST columns under eccentric loads and verified with the experimental results. The stress and strain analyses of core concrete at the ultimate state were conducted by using the FE models. Based on both experimental and finite element methods, the simplified calculation formulae for predicting the ultimate bearing capacity of multi-cell T-shaped CFST columns subjected to axial and eccentric compression were put forward. The calculated results agree well with the results of the test and the FE models.

Experimental research on seismic damage of T-shaped CFST column to steel beam joints

To investigate the seismic damage of T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, eight specimens with the scale of 1/2 were tested under various loadings. The failure modes, load–displacement curves, energy dissipation capacity, cyclic strength degradation, and strain distribution are analyzed. The test results indicate that the failure pattern of the specimens is mainly the shear failure of the joint panel zone and the fracture of the beam end. The hysteretic curves have no remarkable pinch effect, and the joints have excellent energy dissipation capacity. The shear bearing capacity and shear deformation capacity of specimens improve with the growth of depth to width ratio. The seismic damage of specimens with a bigger depth to width ratio develops more slowly. During the mixed loading, the monotonic deformation capacity of specimens decreases significantly with the increase of seismic damage of cyclic loading. Under cyclic loading with constant amplitude, the accumulative damage plays a major role in the failure of the specimens, and the specimens under a bigger constant amplitude are more prone to failure. The column web within the joint panel zone shows a larger damage degree than the column limb.

Behavior of T-shaped CFST column and U-shaped steel-concrete composite beam joints

This paper intends to study the seismic and shear behavior of joints for T-shaped concrete-filled steel tubular (CFST) column and U-shaped steel-concrete composite beam (USCB). In the joint details, the C-shaped slots cut in the T-shaped steel tube allowed the double-C channels used to connect the thin-walled U-shaped steel (USS) passing through the panel zone directly. A total of six full-scale specimens constructed according to the concept of strong column-weak beam were tested: two specimens were tested under the monotonic loading to obtain the load-carrying capacity and the other four specimens under cyclic loading to evaluate the seismic performance . The variables included the details of USCB, the axial load level, and the beam-column linear stiffness ratio . Test results demonstrated that the proposed joint details exhibited good seismic and shear performance. Three typical failure modes, i.e. welding fracture between the double-C channels and the steel tube, local buckling of the steel tube, and fracture of the double-C channels were observed. Some indexes of seismic performances, such as load-carrying capacity, deformability , degradation of load-carrying capacity, stiffness degradation , and energy dissipation capacity were evaluated. Finally, the joint shear resistance of the specimens was discussed according to the ASCE design guidelines. • An innovative joint details for T-shaped concrete-filled steel tubular column and U-shaped steel-concrete composite beam was proposed. • Some indexes of seismic performances for the joints, such as load-carrying capacity, deformability, degradation of load-carrying capacity, stiffness degradation, and energy dissipation capacity were evaluated. • The joint shear capacity was evaluated according the methods given by the ASCE Task Committee and by the previous findings of the authors.

Fire resistance of T-shaped concrete-filled steel tubular columns under eccentric compression

In order to study the fire resistance of T-shaped concrete-filled steel tubular (CFST) columns subjected to eccentric loading, a series of fire tests were conducted along with a numerical study. Specifically, six half-scaled T-shaped CFST columns were tested under the ISO-834 standard fire; and the parameters of stiffener type, load eccentricity, and load angle were considered. The failure modes, thermal response, and structural response were investigated. The test results show that the fire resistance of T-shaped CFST columns decreases with the increase of load eccentricity, but at a lesser degree for relatively high eccentricity. The load angle also has a significant influence on the fire resistance of the columns. A finite element (FE) analysis was then conducted to establish the temperature field model and the thermo-mechanical coupling model which were both validated by the test results. Furthermore, an extensive parametric study including 2008 FE analyses was carried out to investigate the effects of key parameters on the fire resistance of T-shaped CFST columns, including 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), material strength (fy and fck), and load angle (θ). The parametric study indicates that the load ratio n has a significant effect on the fire resistance of T-shaped CFST columns and the other parameters also have certain influences on the fire resistance when n < 0.5. Based on the numerical studies, a simplified method to calculate the fire resistance of T-shaped CFST columns is proposed.

Behavior of T-shaped CFST column to steel beam connection with U-shaped diaphragm

The connection between special-shaped concrete-filled steel tubular (CFST) column and steel beam is a particular concern to engineers. A novel U-shaped diaphragm connection is introduced in this paper to transfer the moment at beam ends in the frame with special-shaped CFST columns and steel beams. Five T-shaped CFST column to H-section steel beam connections were tested under low-cycle horizontal loading. U-shaped diaphragm was used as the connection to transfer loads from beam to joint panel zone. The experimental parameters include the size of U-shaped diaphragm and the axial load ratio of column. Based on the experimental results, the strength, ductility and strain distribution of the connections were calculated. Test results show that the connection can develop plastic bending capacity in the beam, satisfying the design code requirements of America, Great Britain, and China. Furthermore, a parametric analysis was conducted using the finite element method . The influences of U-shaped diaphragm size, tube thickness, and axial load ratio of column were analyzed. Based on the parametric analysis results, a mechanical model is proposed to calculate the yield strength and ultimate strength of U-shaped diaphragm connections. In conclusion, with a proper design, the T-shaped CFST column to H-section steel beam connection using the U-shaped diaphragm can be effectively used in practical applications. • Seismic loading tests are conducted on five large-scale connection specimens. • Finite element model (FEM) is developed and verified with the experimental results. • Parametric study using the FEM is carried out and mechanical model is proposed.

Bearing capacity of welded composite T-shaped concrete-filled steel tubular columns under axial compression

The axial compressive experiments were carried out on 21 welded composite T-shaped concrete-filled steel tubular columns, and 395 finite element models were established for parameter calculation. The calculating formula of axial compressive bearing capacity of welded composite T-shaped concrete-filled steel tubular columns is established. The results show that three typical failure modes were found: middle buckling, end local buckling, and integral bending. When the slenderness ratio λ exceeds the elastic instability limit λp, the axial stress of steel is lower than yield strength fy, and the axial stress of core concrete is lower than axial compressive strength fc. Increasing the thickness of steel has a more obvious effect on increasing the axial compressive bearing capacity of specimen. The theoretical calculating formula can effectively predict the axial compressive bearing capacity, and the theoretical calculation is partial to safety. The average ratio of axial compressive bearing capacity of the theoretical calculation to the experimental is 0.909, and the standard deviation is 0.075. The average ratio of axial compressive bearing capacity of the finite element calculation to the experimental is 0.957, and the standard deviation is 0.045. The average ratio of axial compressive bearing capacity of the theoretical calculation to the finite element calculation is 0.951, and the standard deviation is 0.039.

Experimental behavior of T-shaped concrete-filled steel tubular columns under diagonal cyclic loading

T-shaped concrete-filled steel tubular (CFST) columns have the advantage of avoiding protrusion from walls and can be used as edge columns. The practical structures may be subjected to the earthquake action from different directions, but little attention has been paid to the behavior of T-shaped CFST columns under diagonal cyclic loading. A total of 14 T-shaped CFST columns were tested under constant axial load and lateral cyclic loading. The main variables explored in the test were loading angle, axial load level, concrete compressive strength and section form. The failure mode, lateral load-lateral displacement hysteretic curves, envelope curves, stiffness degradation, ductility, cumulative energy dissipation, deformation and bending moment-curvature curves were investigated. The results show that the hysteretic curves are generally plump and the displacement ductility coefficients are over 3 for the specimens with the axial load levels of less than 0.5. The specimens at 45° and 90° have close envelope curves, while the specimens at 0° exhibit slightly lower lateral ultimate strength and better ductility. The existing codes such as Eurocode 4, AISC 360–10 and DBJ/T 13-51-2010 give obviously higher predictions of initial section flexural stiffness for stiffened specimens without an axial load and conservative predictions for most multi-cell specimens. Furthermore, the existing codes overestimate the serviceability-level section flexural stiffness for most specimens.

Design of L-shaped and T-shaped concrete-filled steel tubular stub columns under axial compression

L-shaped and T-shaped concrete-filled steel tubular (CFST) columns are becoming attractive to researchers and engineers owing to their advantages of avoiding column protrusion from walls and they can save space. In addition, these columns can be used as corner and edge columns in civil engineering applications. Numerous research studies have been conducted on the behaviour of L-shaped and T-shaped CFST columns under axial compression; however, the design methods require further investigation. In this study, finite element (FE) models were developed to simulate the axial behaviour of unstiffened, stiffened, and multi-cell L-shaped and T-shaped CFST stub columns. The FE models were verified by the experimental results of 103 specimens collected from the literature. A parametric study of 804 examples covering a wide range of parameters was conducted based on the FE models. Predictions of the ultimate strength using Eurocode 4 and a previously reported design formula were compared with the FE results, in which unsatisfactory deviations were observed. New design models for the axial compressive strength and the stiffness were proposed by performing regression for different types of L-shaped and T-shaped CFST stub columns.

Study on the behavior of multi-cell composite T-shaped concrete-filled steel tubular columns subjected to compression under biaxial eccentricity

This paper investigates the behavior of multi-cell composite T-shaped concrete-filled steel tubular (MT-CFST) columns subjected to compression under biaxial eccentricity. Nineteen specimens were tested and presented. The main variables were the position and angle of eccentric loading. The experiment showed that the main failure modes of the specimens were overall bending and local buckling. The position and angle of eccentric loading were two important factors that affected the ultimate load of MT-CFST columns. Finite element software was used to analyze MT-CFST columns subjected to compression under biaxial eccentricity. The simulated results were in good agreement with the experimental data. By modifying the relevant parameters, the effect of the strength of concrete, the thickness of steel tubes, and the section dimension on the ultimate load of specimens were investigated. Based on fiber element analysis, the N–M curves and failure surface of the specimens were obtained. According to the fiber element analysis results, a simplified formula was proposed to predict Mx/M0x–My/M0y curves for specimens subjected to compression under biaxial eccentricity. It can be used to check the bearing capability of MT-CFST columns subjected to compression under biaxial eccentricity. The results predicted by the simplified formula coincide with both the results of experimental testing and finite element analysis.

Nonlinear Analysis of Edge Joint on T-shaped Concrete-filled Steel Tubular Column-H-shaped Steel Beam Seismic Performance based on ABAQUS

To comprehensively analyze the seismic performance and failure modes of edge joint, which is composed of T-shaped concrete-filled steel tubular column and H-shaped steel beam, the joint was imposed through low frequency cycling loading. Model of edge joint was established by the nonlinear finite element software ABAQUS. The effect of different parameters, such as axial compression ratio and side plate extension length, on the seismic performance were simulated. The results indicates that the buckling of the steel beam occurs at the lateral extension of the side plate due to the strengthening of the side plate; the axial compression ratio has no obvious effect on the ultimate load; the increase of the side plate length can effectively improve the ultimate load.

Experimental Research on Static Behavior of Stiffened T-Shaped Concrete-Filled Steel Tubular Stubs Subjected to Concentric Axial Loading

Eight stiffened T-shaped concrete-filled steel tubular (CFST) columns and one non-stiffened T-shaped CFST column were tested subjected to axial compressive load in this paper. The mechanical property and failure mode of the specimens were studied. The influences of steel ratio, concrete strength and sectional size were investigated on the axial compressive performance of the specimens. A numerical program was developed to calculate concentric load-shortening curves of T-shaped CFST columns based on experimental results. The confined concrete distribution in T-shaped section and the stiffened tube’s local buckling were considered in the numerical program. A good agreement between calculating results and experimental results was obtained. Besides, a design formula of bearing capacity of stiffened T-shaped CFST columns was put forward by considering favorable effect of stiffeners.

Seismic performance of end-plate connections between T-shaped CFST columns and RC beams

An innovative end-plate connection is proposed by welding an H-shaped steel corbel to the end-plate and the end-plate is connected to the special T-shape concrete-filled steel tubular (CFST) column using a number of high-strength bolts. This paper presents experimental and numerical studies on the seismic performance of the new end-plate connection between T-shaped CFST columns and reinforced concrete (RC) beams with slabs. Tests of seven specimens are conducted: a specimen is tested under the monotonic loading in order to obtain the load-displacement curve and the development of strains until the failure; and six specimens are tested under cyclic loading. The seismic behaviour of the connections in terms of strength, ductility, energy dissipation, strength degradation and stiffness degradation are evaluated. The experimental results demonstrate that the proposed connections exhibit good seismic performance and that the length of the H-shaped steel corbel and the diameter of the high-strength bolt played important roles in improving the seismic behaviour of the connections. A finite element (FE) model based on ABAQUS is developed and validated by the experimental results for the numerical investigation of the seismic behaviour of the proposed end-plate connections. It has been found that the reinforcement ratio of beam and the concrete strength of the beam and slab can affect the seismic performance of the specimens, but the effect of the axial compressive force ratio of the column on the seismic performance can be neglected.

Seismic behaviour of innovative ring-bar reinforced connections composed of T-shaped CFST columns and RC beams with slabs

An extensive set of experimental programme on the behaviour of innovative ring-bar reinforced connections composed of T-shaped concrete-filled steel tubular (CFST) columns and reinforced concrete (RC) beams with slabs are reported in this study. Specifically, for the proposed connection, the T-shaped CFST column is welded with an H-shaped steel corbel, which is embedded into the reinforced concrete beam and slab. Moreover, a few ring-bars are fabricated to improve the seismic resistance capacity of this connection. A total of six specimens are tested: one specimen is tested under monotonic loading to investigate the load-displacement relationship and the development of strains; and the other five specimens are tested under cyclic loading to obtain the seismic behaviour of these specimens. The test results demonstrate that the seismic behaviour of the proposed connections is prominent and that the diameter and number of ring-bar and length of steel corbel are found to be significant factors of the seismic behaviour of the connections. Complementary to the experiments, a finite element (FE) model is developed to further analyse the experimental results by illustrating the failure modes of the specimens and extending the parametric studies which are not studied through the limited experiments. The comparison between the FE analysis and the experimental results demonstrates the accuracy of the proposed model. Numerical results indicate that the ring-bar and slab are able to increase the stiffness and bearing capacity of the specimens; the reinforcement ratio of beam, the concrete strength of the beam and slab play important roles in improving the ultimate strength of the specimens.

Numerical analysis on seismic behaviors of T-shaped concrete-filled steel tubular columns with reinforcement stiffeners

A numerical analysis based on previous experiment has been carried out on T-shaped concrete-filled steel tubular columns subjected to constant axial compressive load and cyclic lateral loads. Tensile bar stiffeners were introduced to be welded on inside surfaces of steel tube to postpone its local buckling and to enhance the confinement of steel tube for concrete. A modified fiber-based method was developed to establish numerical modeling program of specimens’ cyclic behavior, incorporating the effect of stiffeners on postponing steel tube’s local buckling and the confinement for concrete. The reciprocating movement of inflection point along frame column is also considered in the numerical program. A simplified arc-length method was employed as iterative control algorithm of the numerical model. Horizontal load–displacement hysteretic curves of specimens were calculated with the numerical model and verified with test results. A restoring force model based on experimental investigation was proposed as simplified method for engineering practice.