Steel Tube Thickness Research Articles

Seismic behavior of steel-plate encased concrete shear wall with paralleled circular CFST columns: Laboratory test and numerical simulation

Aiming to improve the structural behavior of high-rise buildings, a steel-plate encased concrete shear wall with parallel circular concrete-filled steel tube columns (P-CFST-SCSW) is proposed and investigated by experiments and numerical studies in this study. All seven specimens were conducted and tested under reversed cyclic force to explore the influences of different design parameters, including axial compression ratios, steel tube thicknesses, spacing-thickness ratios, and shear span ratios. The failure modes, hysteresis behavior, strength and stiffness degradation, energy dissipation were thoroughly recorded and compared in detail. Results indicated that all specimens have experienced the failure process of boundary steel tubes buckling, steel plates buckling and concrete crushing. Results also showed that the bearing capacity and deformation capacity of proposed composite walls was excellent. The peak force and initial stiffness of P-CFST-SCSWs were improved by reducing the shear span ratio and increasing the axial compression ratio, while the stiffness degradation and ductility quickly deteriorated. The increased thickness of circular steel tubes considerably improves the seismic behavior of P-CFST-SCSWs. Finally, the numerical model was established to further investigate the effect of the concrete strength, steel yielding strength, and circular CFST columns number on lateral behavior of P-CFST-SCSWs.

Experimental investigation of FRP-confined HSC-filled steel tube stub columns under axial compression

In this study, the axial compressive properties of fiber-reinforced plastic (FRP)-confined high-strength concrete-filled steel tube (HSCFST) stub columns were investigated, and the effects of the steel tube thickness, FRP type, concrete strength, and number of FRP layers were analyzed. The results reveal that fracturing of the FRP and bulging deformation of the steel tube are apparent when the stub column fails. An increase in the concrete strength, thickness of the steel tube, and number of FRP layers effectively improve the ultimate strength of the stub column. Compared with carbon fiber-reinforced plastic (CFRP), glass fiber-reinforced plastic (GFRP) has a more evident effect on improving the ultimate strength and delaying the stiffness degradation of stub columns. Further, a finite element model that accurately simulates the axial compressive behavior of FRP-confined HSCFST stub columns was established to better understand the stress development of the high-strength concrete (HSC), steel tube, and FRP. In addition, a calculation method for the peak strain and ultimate strength of FRP-confined HSCFST stub columns subjected to axial compression loads was developed; this method can accurately predict the actual test results.

Experimental study of bamboo scrimber-filled steel tube columns under axial compression

A new bamboo scrimber-filled steel tube (BSFST) structure consisting of a steel tube with bamboo scrimber is presented. The proposed structure can be used as an alternative to nonrenewable construction materials. To investigate the axial behavior of the structure, thirty bamboo scrimber and thirty BSFST columns were tested under axial compression. Specimen size and steel tube thickness were used as the test parameters. The results showed that for the unconfined bamboo scrimber, the failure mode changed from shear failure to split failure, and the ultimate stress decreased gradually with increasing specimen size. Based on the test results, the ultimate stress relationship between different sizes of bamboo scrimber was clarified, and a formula for the size effect was proposed. For the BSFSTs, the main damage mode was shear damage. With increasing steel tube thickness, the mechanical properties of the specimens increased greatly. Formulas for the calculation of the ultimate stress and ultimate strain of BSFST were proposed. According to the stress–strain curves of the BSFSTs, the characteristic points were defined, a formula for the calculation of characteristic points was suggested, and models of complete stress–strain curves BSFSTs were proposed. The proposed models accurately predicted complete stress–strain curves of the specimens used.

Axial compressive behavior of steel fiber reinforced concrete-filled square steel tube stub columns

This study aims to assess the influence of steel fiber on the mechanical property of concrete-filled square steel tube (CFSST) stub columns. A total of 36 specimens, with different concrete strength grades (C = 40 MPa, 50 MPa or 60 MPa), various steel tube thicknesses (t = 3 mm, 3.75 mm or 4.5 mm) and diverse steel fiber volume contents (Vf = 0%, 0.6%, 1.2% or 1.8%), are conducted under axial compressive loading. Failure modes, ultimate loads, load-displacement behavior and relative load-strain behavior are discussed. Moreover, a finite element (FE) model is proposed to investigate the reinforcing mechanism of steel fibers in CFSST columns. The test results show that the ultimate bearing capacity of CFSST columns slightly increases with the increasing of steel fiber volume content, but the energy dissipation capacity and ductility are visibly improved. However excessive steel fibers (exceeding 1.2% in this study) may cause a negative effect. FE analysis demonstrates that steel fibers with a moderate amount not only postpone the failure of concrete core, but also improve the carrying loads of concrete core at ultimate state. Finally, a design formula is put forward for the ultimate bearing capacity of CFSST stub columns.

Behaviour of square concrete-filled steel tubes reinforced with internal latticed steel angles under bending

The bending properties of square CFSTs (concrete-filled steel tubes) reinforced with internal latticed steel angles were experimentally investigated through four-point bending test, and test results of moment vs deflection curves, moment vs strain curves, bending capacity and concrete cracks were acquired, the test results showed that the latticed steel angles can restrain the cracking of concrete and delay the upwards movement of the neutral axis. After the experiment, firstly, the corresponding finite element (FE) models were established by ABAQUS and validated through comparison with test results; secondly, the bending mechanisms of the tested specimens were analysed and discussed; thirdly, the parametric analysis was conducted to investigate the influence of the main parameters, such as the yield strength and thickness of steel tube, the yield strength and area of latticed steel angles. The research results indicated that the steel tube contributed the most to the bending capacity, hence the yield strength and thickness of steel tube have the most significant influence on the bending capacity. Moreover, the design equations for the bending capacity were proposed based on the superposition method and plastic stress distribution method, and the calculation results showed that the design equations can conservatively and safely predict the bending capacity.

Behavior of ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stub columns under axial compression

A total of seventeen ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stub columns and one normal concrete encased CFST stub column were tested under axial compression. The influence of steel fiber content, diameter of steel tube, wall thickness of steel tube and strength of core concrete on the failure mode, axial load-axial strain curve, axial compression bearing capacity and ductility of the members was experimentally investigated. Furthermore, finite element model of UHPC encased CFST stub column subjected to axial compression was established. Based on the verified finite element model, typical axial load-axial strain curve, load distribution proportion, stress development and interaction between different components of the members were analyzed in depth. Parametric studies were performed to clarify the influence of steel fiber content of UHPC, CFST ratio, wall thickness of steel tube, steel yield strength, core concrete strength and stirrup spacing on the behavior of the members. At last, a simplified formula for calculating the axial compression bearing capacity of UHPC encased CFST stub columns was proposed, which could provide reference for practical engineering applications.

Experimental and numerical study on axial compressive behaviors of reinforced UHPC-CFST composite columns

To improve the fragility of UHPC columns, reinforced UHPC-concrete filled steel tube (RU-CFST) columns conjugated of peripheral reinforced UHPC and inner CFST were proposed. An axial compressive test program consisting of three RU-CFST columns and one reinforced UHPC (RU) column was conducted to study the effects of steel tube thickness and stirrup spacing on the compressive behaviors of RU-CFST columns. The test results indicated that the sudden drop of load beyond the ultimate load was effectively improved and the compressive strength as well as ductile of the RU-CFST columns were significantly promoted compared to that of the RU column. Based on the experimental results, three-dimensional FE models were developed to simulate the axial compressive performance of the RU-CFST columns, and their accuracy was confirmed by the test results. With the validated FE model, the effects of steel tube thickness, stirrup spacing and core concrete strength on the compressive behaviours of RU-CFST columns were further investigated. Finally, calculating method considering the contribution ratio of the inner CFST component was developed to predict the ultimate bearing capacity of the RU-CFST columns.

Structural Behavior of Short Thin-Walled Steel Columns Filled with High Strength Concrete Made of Recycled Aggregate

This paper introduces an experimental work to study the behavior of 12 recycled aggregate concrete-filled steel tubular (RACFST) short columns with high-strength concrete grade subjected to axial compression loading. These columns formed from six different cross-sections involving triangle, elliptical, and hexagon, whereas the other three sections included traditional forms for control purposes, involving square, rectangular, and circular. All RACFST columns used are made of mild steel plates. These columns were divided into two groups. The steel tube thickness was the only parameter modified to study its effect properly. In addition, the study included the search for the best effective section concerning the properties of stability and confinement, so these columns were designed so that the cross-sectional areas of steel tubes were approximately equal. Also, composite action and level of ductility for these columns were studied. The ultimate failure axial load, the reduction in the axial column length, the failure pattern of cross-section shape, and lateral displacement were recorded during the test. Regarding the two groups of columns with (1 and 2) mm thick steel plates, testing data obtained from RACFST columns with elliptical and circular cross-sections respectively showed better stability and confinement of concrete and the ability to withstand a higher ultimate failure stress. Moreover, columns with polygonal sections showed when the number of ribs for the steel plates of the model or increased the angle between the two sides is (90°) or more, column cross-sections can achieve more stability and confinement, respectively. In general , increasing the thickness of the steel tubes increases. Finally, for all columns, the higher values of the concrete contribution ratio (C.C.R) led to an increase in the strength index (S.I.) values. An increase in values of final failure stresses accompanied this increase.

Experimental study on the behavior of CFRP-high strength concrete-steel double skin tubular columns subjected to axial compression

This paper discusses the findings of an experimental investigation into the axial compressive behavior of fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) made using high-strength concrete. DSTCs are composite columns that consist of an inner steel tube, an outer FRP tube, and concrete in between. The diameter and wall thickness of the inner steel tube in DSTCs served as the test parameters for this investigation. 21 cylindrical specimens with a diameter of 152 mm and a height of 305 mm were fabricated from high-strength concrete with a compressive strength of 55.9 MPa and subjected to monotonic axial compression. The findings from this experimental investigation demonstrate that as the diameter of the inner steel tube grows the load capacity of the DSTCs decreases, with this impact being dependent on the thickness of the outer FRP tube. In addition, the load capacity of the DSTCs increases as the thickness of the inner steel tube increase, independent of the thickness of the outer FRP tube.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Effect of Debonding on Axial Response of Concrete Filled Steel Tubular Columns

The axial strength and ductility of concrete filled steel tubes is significantly improved due to two major factors namely, firstly due to confining effect provided by steel tube, and secondly due to the synergistic interaction between steel tube and concrete core. Sometimes, the contact between concrete core and steel tube is vanished and debonding between concrete core and steel tube (normal referred as gap) occurs owing to various reasons such as improper compaction, shrinkage in concrete, lack of curing of encased concrete, and due to non-uniform distribution of load at column top. Due to occurrence of gap, the composite action between concrete core and steel tube no longer remains effective the concrete core becomes unconfined in the initial phase of loading, consequently, the axial load carrying capacity of the concrete filled steel tubular (CFST) column decreases. The aim of this paper is to numerically investigate the effect of the gap between concrete core and steel tube on the axial load-deformation response and to Comparisons the predicted column strengths according to the Eurocode-4. In the present study, the gap between square section concrete core and encasing steel tube is considered on all the four sides with the magnitude of gap as 1 mm and 2 mm. Moreover, in order to investigate the effect of the gap on different size of square section CFST columns, keeping the length of column and steel tube thickness as constant 540 mm and 3.8 mm respectively, the side length of square section CFST column has been varied between 140 mm to 200 mm at an interval of 20 mm. The nonlinear finite element analysis of the CFST columns has been performed using the Abaqus where the C3D8R element has been used to discretize the concrete core as well as steel tube and the Drucker-Prager model has been used to simulate plastic behaviour of concrete. It has been observed that the presence of gaps between concrete core and steel tube significantly reduces the axial strength square CFST column.

Non-linear Analysis of Axially Loaded Octagonal CFDST Short Columns

Concrete Filled Double-skin Steel Tube (CFDST) is a form of composite column that consists of outer steel and an inner steel tube and the space between them is filled with concrete. The structural response of CFDST columns is significantly affected by the thickness of outer and inner steel tubes and the compressive strength of infilled concrete. Although many studies have been in the past to understand the effect of inner and outer tubes thickness on the axial compressive response of circular CFDST columns, no such study appears in the context of octagonal CFDST columns. In this paper, the thickness of both inner and outer tubes is varied. Their effect on axial compressive behavior of CFDST columns containing the concrete of different grades is numerically examined. The non-linear FE analysis of CFDST columns is performed using the ABAQUS. The study shows that axial strength and ductility of octagonal section CFDST columns are significantly influenced by steel tube thickness and the grade of sandwiched concrete. Moreover, the study highlights the importance of the proper selection of inner and outer tube thickness for the better axial response of CFDST columns.

Experimental and numerical investigations of bolted assembled joints to concrete encased CFST columns with different connection details

Concrete encased CFST (CECFST) composite components have prominent advantages over traditional CFST components such as better durability, high stiffness and strength, etc. However, the encased concrete outside caused certain difficulty in connecting to the steel beam. In this paper, two types of bolted assembled joints between CECFST column and steel beam were proposed and tested under cyclic loads, in which the end plate and cover plate joints were included. Typical failure modes of the joints were analyzed and characterized. In comparison, the CECFST column in end plate joints exhibited more severe failure and higher strength than that in cover plate joints. Seismic performance including hysteretic curves and energy dissipation were also discussed. In addition, numerical modelling of the joint was established considering the complicated material models and interactions in the joint core, of which the accuracy was validated against the test results. Further, parametric analyses were performed on the cover plate joints with CECFST columns through the numerical approach. It demonstrated that the axial ratio, thickness and strength of cover plate, diameter of bolt, strength and thickness of steel tube significantly affected the stiffness and strength of the joint. The experimental and numerical results revealed that the proposed two types of joints with CECFST column performed relatively favorable seismic behavior and could be employed in engineering practice.

Behaviour of CFRP confined square concrete-filled stainless steel tubular columns under uni-axial compression

To study the behaviour of the carbon fibre-reinforced polymer (CFRP) confined square concrete-filled stainless steel tubular (CFSST) stub column, three square CFSST stub columns and nine CFRP confined square CFSST stub columns were tested under axial compression. The test parameters included the number of CFRP sheet layers and the thickness of the stainless steel tube. The test results showed that failure modes of all CFRP confined square CFSST stub columns were the fracture of CFRP sheets and the outward local buckling of the stainless steel tube at the chamfering. The typical load–displacement curves of the tested columns exhibited four stages, i.e., elastic stage, elastoplastic stage, descending stage and residual stage. CFRP sheets could restrain the local buckling of CFSST, and improve the ultimate bearing capacity and the ductility index of the columns. With the increase in the number of CFRP sheet layers and the wall thickness of the stainless steel tube, the bearing capacity of the column increased linearly. Based on the twin-shear unified strength theory, a calculation method of the ultimate bearing capacity of the square CFSST stub column was proposed. Besides, through the superposition method and regression analysis, two simplified methods to predict the ultimate bearing capacity of CFRP confined square CFSST stub column under axial compression were obtained.

Experimental and analytical study of square tubed concrete-encased cross-shaped steel (TCCS) columns under axial compression

This paper presents an experimental and analytical study on square tubed concrete-encased cross-shaped steel (TCCS) columns under axial compression. The effect of test variables covering the steel section types (Type B and L), steel tube thicknesses (2.75, 5.00 and 7.50 mm) and external CFRP layers (0, 1, 2 and 4) on the mechanical behavior of the specimens were investigated. The test results show that obvious local buckling of the flange is mainly observed in the specimens embedded with Type B steel section with a larger width-thickness ratio and severe concrete crushing is also detected in the corresponding position. The constraint provided by the flange of the Type B steel section in suppressing the lateral deformation of inner concrete is weaker than that of the Type L section, leading to the inferior behavior of load capacity, ductility, and energy absorption, whereas the impact of steel section type becomes less significant to the dilation behavior of TCCS columns with sufficient confinement provided by the external tube. Furthermore, the confinement mechanism of steel section confined concrete is interpreted based on the buckling theory, and the stress–strain model of confined concrete in TCCS columns is proposed by considering the dual confinement from external tube and steel section. Finally, an analytical model is developed to predict the load–strain relationship of TCCS columns according to the section analysis method. By comparing the predictions with the experiments in this paper and several existing literature, it can be found that the proposed analytical model possesses satisfactory accuracy and applicability.

Behavior of concrete-filled T-shaped steel tubular beam-columns under biaxial compressive loads

Concrete-filled T-shaped steel tubular (CFTST) columns have a wide prospect of being used in high-rise buildings to avoid having protruding portions in walls. This paper presents an experimental and theoretical study on CFTST beam-columns under biaxial compressive loads. Five full-scale CFTSTs, including an axially loaded column and four biaxially loaded beam-columns, were tested and the failure modes, lateral deflections and strains were discussed. Current design methods originally for rectangular CFSTs offered a much conservative prediction for the tested T-shaped specimens as the cross-section is single-symmetric. Based on fiber element analysis, parametric study was conducted to investigate the effects of key parameters on the interaction curves that were normalized by the moment capacity of the specimen under uniaxial eccentric compression. Concrete strength, steel yield stress and steel tube thickness have insignificant effects on the normalized interaction curves but the influences of axial force ratio, cross-section dimensions and slenderness ratio are obvious. Finally, empirical interaction formulas in both complex and simplified forms were proposed for CFTSTs under biaxial eccentric loads. Accuracy of the proposed method was then verified by the experimental results and fiber element analysis results.

Experimental Study on Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns

Concrete-filled steel tubes present excellent structural and constructional performances because they ideally combine the advantage of concrete and steel tube. Thus, they are widely used in civil infrastructures. However, they inevitably suffer from either hard compacting or high costs. Thus, convenient and rapid construction for compacting concrete and cost saving are the urgent challenges for concrete-filled steel tubes. Therefore, this study investigates filling a thin-walled steel tube with self-compacting concrete to solve the challenges presented by traditional concrete-filled steel tube columns, such as poor compacting performance and high costs. This experimental study tests self-compacting concrete-filled thin-walled steel tube (SCCFTST) columns under concentric compression from loading to failure. Effects of wall thickness of the thin-walled steel tube on the failure modes, load-deformation behaviors, and the ultimate loads of the SCCFTST columns are comprehensively investigated. The ultimate loads between experiments and their calculated values in terms of design codes are also compared. The results suggest that buckling on thin-walled steel tube surface is the typical failure mode. The amount of local buckling increases with decreasing wall thickness, and the decreasing rate of the load-deformation curves in the descending branch decreases by increasing the wall thickness, as well as the ultimate load increasing with increases wall thickness. The ACI and CECS are the most conservative and accurate design codes, respectively, for predicting the ultimate load. Therefore, the SCCFTST columns can be used as structural components in civil infrastructures and their peak loads can be calculated using design codes for conventional concrete-filled steel tube columns. However, modification measures must be taken while predicting the ultimate loads of the SCCFTST columns by design codes. The experimental results of this paper can contribute towards the application of SCCFTST columns in practice.

Seismic behaviors of T-shaped steel-concrete-steel sandwich composite walls using enhanced C-channels

This paper developed the T-shaped steel-concrete-steel sandwich composite (TSCSSC) walls using enhanced C-channels, and investigated their seismic behaviors through three cyclic loading tests. The parameters studied in the cyclic loading test programme included wall thickness of the steel tube in boundary CFST columns and aspect ratio of TSCSSC wall specimens. The test results showed that TSCSSC walls exhibited flexural failure modes characterized by infilled-concrete crushing, tensile fracture of steel tubes, weld seams, and local buckling of steel faceplates and tubes. The skeleton hysteretic P-Δ curves of TSCSSC walls exhibited a typical three-stage working mechanism, i.e., elastic, nonlinear development, and recession stage. Increasing the thickness of steel tubes in the web wall improved the strength and energy dissipation capacities. Reducing the aspect ratio of TSCSSC walls improved strength and stiffness, but exhibited lower peak bending resistance owing to the effect of acting shear force on wall-base cross section. Finally, prediction equations were developed to estimate the peak bending resistance of TSCSSC walls. Validations against reported test results confirmed their limited prediction errors (≤10%). • T-shaped steel-concrete-steel sandwich composite (TSCSSC) walls with enhanced C-channels is proposed. • TSCSSC walls exhibited flexural failure and plump hysteretic load-drift behavior. • Increasing the wall-thickness of boundary steel tube improves seismic behaviors of TSCSSC walls. • TSCSSC walls with low aspect ratio failed in combined flexure and shear mode. • Developed prediction equations predict well the bending resistance of TSCSSC walls.