Steel Tubular Beam-columns Research Articles

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 investigation of concrete-filled double-skin stainless steel tubular beam-columns

This paper presents an experimental investigation of the hysteretic behavior of concrete-filled double-skin stainless steel tubular (CFDSST) beam-columns with circular hollow section (CHS) outer and inner. A total of 18 specimens were designed and tested under constant axial compressive load and cyclically increasing flexural load to investigate the structural performance of the composite beam-columns and evaluate the effects of varied design parameters, including the thicknesses of the CHS outer and inner and concrete strength, on the performance of the hysteretic behavior of the CFDSST beam-columns. Both of the lateral load (P) versus lateral displacement (Δ) hysteresis response and moment (M) versus drift angel (θ) hysteresis response were obtained. Based on which, the failure mechanism, ductility, energy dissipation capacity, stiffness degradation, and ultimate strength of the specimens were investigated. The results show that the specimens failed in a ductile mechanism features bulge and rupture at the bottom of the CHS outer, unimpaired CHS inner, and local concrete crush, demonstrating the combined effect of the stainless tubes with the concrete. All of the specimens showed high level of ductility and energy dissipation capacity. Finally, comparisons of ultimate bending moments of the beam-columns between the test results and predictions from the existing design codes and design method demonstrate the deign codes underestimates bending moment strength of the CFDSST beam-columns.

Experimental and theoretical study on concrete-filled T-shaped steel tubular columns under uniaxial eccentric compression

This paper presents an experimental and theoretical study on concrete-filled T-shape steel tubular (CFTST) beam-columns. Four full-scale slender beam-columns with slenderness ratio of 33.7–39.1 were tested under uniaxial eccentric compressive loads. In addition, three stub columns with the same cross-sections were axially compressed to investigate the confinement effect. Failure mode, axial displacement, lateral deflection, axial strain and hoop strain were obtained to understand the structural behavior of CFTST beam-columns. For beam-columns bended about the symmetric axis, torsion was not observed but a slight rotation of the neutral axis that was no longer parallel to the centroid axis was found by analyzing the experimental results. A fiber element model for CFTST beam-columns was developed and verified for parametrical analysis. The effects of key parameters, such as material properties, cross-section dimensions, loading angle and slenderness ratio, on the behavior of stub and slender beam-columns were investigated. Finally, theoretical models were proposed to estimate the interaction curve and the load-carrying capacity of CFTST beam-columns. The prediction matches well with the experimental results.

Experimental analysis on circular concrete-filled steel tubular beam-columns under unequal load eccentricities

This paper presents eight experimental tests on circular concrete-filled steel tubular (CFST) beam-columns loaded under unequal eccentricities at both ends. This loading scheme has not been widely studied yet in previous research works on CFST columns, but it may be very common into industrial or residential multi-storey frames, where both ends are subjected to different bending moments. Tests results revealed that the ultimate resisting load increases when the column is loaded under unequal eccentricities compared to what is loaded under equal eccentricities. However, under certain conditions, the column ductility decreases. Also, the equations provided by the Eurocode 4 and AISC 360–16 for second order effects were assessed. Specifically, the equivalent moment factors, βor Cm, were calculated from experimental data and compared to those given by the standards. Although Eurocode 4 presents more accurate predictions, both codes provide safe predictions for higher slenderness beam-columns but unsafe predictions for double curvature members with low slenderness. In view of the results, further research is needed to improve the equivalent moment factor proposals including additional parameters apart from the loading eccentricity ratio.

Testing, modelling and design of normal and high strength steel tubular beam-columns

The influence of yield strength on the in-plane stability and design of structural steel square and rectangular hollow section (SHS and RHS) beam-columns under compression plus uniform bending is investigated in this study. Ten buckling tests were carried out on hot-finished S690 SHS 100×100×4 (in mm) specimens under combined compression plus uniaxial bending. Finite element (FE) models of SHS and RHS beam-columns were established, validated and employed to perform parametric studies, where supplementary buckling resistance data were numerically derived. Through comparisons with the test and FE data, shortcomings of the current EC3 beam-column interaction curves were revealed, particularly in the higher yield strength domain. A modified EC3 approach was developed accordingly, featuring more accurate compression end points and re-calibrated interaction factors, and was shown to significantly improve the design accuracy and consistency for both hot-finished and cold-formed SHS and RHS beam-columns over a wide spectrum of steel grades. Subsequent reliability analysis confirmed the applicability of the current EC3 partial safety factor to the proposed modified EC3 design approach.

Cold-formed high strength steel tubular beam-columns

High strength steel is used more often in a variety of civil engineering applications due to its high strength-to-weight ratio and cost effectiveness. This paper presents the experimental investigation on cold-formed high strength carbon steel tubular members subjected to combined compression and bending. The nominal 0.2% proof stresses of the test specimens were 700 and 900 MPa. The test specimens consisted of square hollow sections (SHS), rectangular hollow sections (RHS) and circular hollow sections (CHS). The material properties, global geometric imperfections of the specimens were measured. The behaviour of the beam-column members was investigated through testing 32 specimens which had a nominal member length of 1480 mm. The second order effects were also considered by measuring the mid-height deflections for all specimens. The compression and bending capacities, load-deformation histories and failure modes of the test specimens were also reported. The test results were compared with the values predicted from the American, Australian and European standards. Improved design recommendation is provided for cold-formed high strength steel tubular beam-columns. Based on the experimental results, finite element modelling methodology is also proposed.

Local damage identification of high-strength circular concrete-filled steel tubes under low cycle fatigue

This paper investigates the low cycle fatigue (LCF) induced damages of high-strength circular concrete-filled steel tubular (CFT) beam-columns subjected to nonstationary loading history. The test specimens are fabricated by ultra-thin walled steel tubes with 2 mm in thickness to clarify the vulnerability concerning fatigue failure, and to evaluate the fatigue life of slender and over-design circular CFT beam-column members. Experimental results indicated that the specimens with a large D/t ratio together with thin-walled steel tubes tend to trigger highly-concentrated local buckling at column bottom where sequentially experienced premature fractures due to low cycle fatigue and the fragmentation of concrete infill. This complex LCF-induced failure mode can be identified by developing a new damage detection technique using polymer optical fiber sensors with distributed placement. It is found that the sequence of variable amplitudes during LCF history plays significant influences on the accumulation of plastic deformation which is not necessarily correlated to the sequence of nonstationary loading history induced by earthquake ground motions. Moreover, the epistemic uncertainty of variable amplitude of displacement demonstrates considerable influences on fatigue life with variable displacement amplitudes.

Post-local buckling failure of slender and over-design circular CFT columns with high-strength materials

This paper investigates the ultimate behavior and post-local buckling failures of circular concrete-filled steel tubular (CFT) beam-columns under cyclic loading with constant axial force. The test specimens are fabricated by thin-walled steel tubes with 2 mm in thickness to clarify the main failure modes, and to evaluate the ultimate flexural behavior of slender and over-design circular CFT columns. Test results indicated that the column specimens with a large D/t ratio together with a thin-walled steel tube tend to trigger highly concentrated local buckling at column bottom where sequentially experienced low cycle fatigue fracture and the fragmentation of concrete infill. From the orthogonal analysis on the test results, it is found that the D/t ratio and concrete-to-steel strength ratio respectively play the most significant influences on the ultimate flexural strength and the critical axial load ratio. Finally, the fiber element model incorporating strength and stiffness degradation can accurately predict hysteresis behavior. This study provides fundamental supports for the design and analysis of thin-walled steel tubes to circular CFT columns with slender cross-section.

Mechanical Behavior of Circular Steel Tubular Beam-Columns Corroded Uniformly in Atmospheric Environment

Circular steel tube members with the absence of anticorrosive protection or coating failure are prone to uniform corrosion, which threatens the reliability and safety of members in the atmospheric environment. To fully study the mechanical behavior of uniformly corroded circular steel tubes, compression test and theoretical analysis were conducted, and two methods considering section reduction and material degradation, respectively, were adopted for the calculation of ultimate load carrying capacities of specimens. The results indicate that uniform corrosion did not change the failure modes of specimens, and all of them belonged to global buckling failure. The load carrying capacities and stiffness of specimens decreased with the increase of corrosion ratio, and the degree of reduction was greater than that of material degradation, showing a linear relationship with the corrosion rate. Under the same corrosion ratio, the specimens with larger eccentricity represented more obvious load carrying capacity and stiffness degradation. The load carrying capacities predicted by both methods were in good agreement with the test results and had a certain safety margin. The conservative degree of calculation results from three specifications followed a descending order of ANSI/AISC 360-16, GB 50017-2017, and EN 1993-1-1. Under the same corrosion ratio, the load carrying capacity variation of specimens between one-sided corrosion and two-sided corrosion was less than 3%.

Experimental and numerical studies of square concrete-filled double steel tubular short columns under eccentric loading

Square concrete-filled double steel tubular (CFDST) beam-columns consisting of an internal circular steel tube have increasingly been utilized in composite building structures because of their high structural performance. This paper describes experimental and numerical studies on the structural responses of square thin-walled CFDST columns loaded eccentrically. Tests on twenty short square CFDST columns were undertaken that included sixteen columns under eccentric loading and four columns under concentric loading. The parameters examined in the experiments included the cross-sectional dimensions, the width-to-thickness ratios of outer and internal tubes and loading eccentricity. The measured ultimate strengths, load-shortening responses, load-lateral displacement curves, stress-strain curves and observed failure modes are presented. A numerical model incorporating the fiber analysis is developed that predicts the moment-curvature responses and axial load-moment strength envelops of CFDST columns. The model explicitly accounts for the influences of the confinement exerted by the internal circular steel tube on the core concrete and the progressive post-local buckling of the external steel tube. Efficient computer algorithms implementing the inverse quadratic method is developed to produce converged solutions to the nonlinear dynamic equilibrium equations generated in the analysis. Measurements from the tests are employed to validate the proposed numerical model. It is shown that there is a good agreement between theory and experiment. The computer model is utilized to demonstrate the significance of various parameters on the behavior of thin-walled short CFDST beam-columns.

Behaviour of square CFST beam-columns under combined sustained load and corrosion: FEA modelling and analysis

This paper presents a numerical investigation on concrete-filled steel tubular (CFST) beam-columns with square sections subjected to combined sustained load and corrosion. A general numerical method is used for the simulation of the time dependent behaviour of the core concrete, while the wall-thickness loss of the outer steel tube induced by corrosion is considered in this model simultaneously. The established finite element analysis (FEA) modelling is verified with test data and used for further investigations of the load-deformation relationship, load-transfer mechanism, stress and strain development, failure modes and ultimate states on CFST beam-columns when suffering combined sustained load and corrosion. Parametric studies are conducted to reveal the effects of key parameters, based on which simplified design method is suggested for square CFST beam-columns under combined sustained load and corrosion.

Behaviour of square CFST beam-columns under combined sustained load and corrosion: Experiments

This paper presents an experimental study on concrete-filled steel tubular (CFST) beam-columns with square sections under combined sustained load and chloride corrosion. A total of 11 specimens (including 7 CFST members and 4 reference hollow steel tubes designed for comparison) were tested under 120-day sustained load in accelerated chloride corrosion environment and then loaded to failure. The main test parameters include load ratio (ratio between the long-term sustained load and the ultimate capacity of the specimen under short-term loading) and corrosion depth. The failure modes, full-range load-displacement relationship, load-strain relationship and ductility were measured and compared. Based on the experimental observation, mechanism of CFST beam-column members under the combined effects of sustained load and chloride corrosion was discussed and compared to the reference hollow steel tubes. Traditional design methods were modified for the consideration of combined sustained load and corrosion, which were calibrated and evaluated against the test results.

Experimental assessment of the cyclic behaviour of concrete-filled steel tubular beam-columns with octagonal sections

This paper presents an experimental investigation on concrete-filled steel tubular beam-columns with octagonal cross-sections (OCFST) under cyclic lateral loading with or without axial load. A total of nine specimens with different parameters, including the axial load level (n) ranging from 0 to 0.5 and concrete compressive cylinder strength (fc′) varying from 30 MPa to 90 MPa, were tested. The failure modes, ultimate strengths, displacement ductility, effective flexural stiffness and cumulative dissipated energy are presented. The results indicate that OCFST beam-columns exhibit a ductile plastic mode and excellent energy dissipation. With the increase of axial load level, the ductility and the energy dissipation capacity decreases, while the ultimate bending capacity firstly increases then drops. Concrete grades seem to have limited influence on the ultimate strength and energy dissipation capacity. The comparison results of the ultimate bending moments and effective flexural stiffness between predictions using EN 1994-1-1 and AISC 360-16 and test results reveal their applicability to the design of OCFST beam-columns.

Experimental characterization of steel tubular beam-columns resistance by means of the Overall Interaction Concept

This paper presents a series of twelve buckling tests on rectangular and circular hollow section beam-column of nominal steel grade S355. The columns were fabricated by either the hot-rolling or the cold-forming process, and were subjected to different load cases through the application of eccentric compression: mono-axial bending (My) or bi-axial bending (My + Mz) combined with axial compression (N). Preliminary measurements of cross-section geometry, material properties, geometrical imperfections, residual stresses as well as stub column tests are also reported in this paper. The (imperfect) initial geometry was measured along the whole column by means of two different procedures; the first method relied on the use of a set of equally spaced Linear Variable Displacement Transducers (LVDTs) displaced on each specimen's plates. The second method consisted in scanning the specimen's plates by means of a laser Tracker AT401. Residual stresses were also determined experimentally, and the sectioning technique was classically used to record the deformations of the released material; these results have been compared to measurements taken with electrical strain gauges. Finally, beam-column buckling strengths were plotted in an O.I.C.-type format, and complemented with an extensive experimental data collected from the literature that comprised various load cases, fabrication processes, yield strengths, cross-sections shapes, and elements’ lengths. The O.I.C. approach was shown to adequately capture the behavior of hollow section beam-columns in a straightforward and simple manner, and its potential for efficiently and rationally predicting carrying capacities was evidenced.

Nonlinear analysis of biaxially loaded rectangular concrete-filled stainless steel tubular slender beam-columns

Rectangular concrete-filled stainless steel tubular (CFSST) beam-columns utilized as supporting members for building frames may experience axial compression and biaxial moments. A numerical simulation considering the local buckling effects for thin-walled rectangular CFSST slender beam-columns has not been performed. This paper reports a stability modeling on the structural characteristics of rectangular CFSST slender beam-columns accounting for different strain-hardening of stainless steel under tension and compression. The influences of local buckling are considered in the simulation utilizing the existing effective width formulations. The developed numerical model simulates the strength interaction and load-deflection behavior of CFSST slender beam-columns. Comparisons of computed results with test data provided by experimental investigations are performed to validate the proposed fiber model. The influences of different geometric and material property on ultimate strengths, ultimate pure moments, concrete contribution ratio, strength interaction and load-deflection responses of CFSST slender beam-columns are examined by utilizing fiber model. A design formula considering strain hardening of stainless steel is derived for calculating the ultimate pure moment of square CFSST beam-columns.

Cyclic loading tests on concrete-filled double-skin (SHS outer and CHS inner) stainless steel tubular beam-columns

This paper reports a series of cyclic loading tests on concrete-filled double-skin stainless steel tubular (CFDSST) beam-columns with square hollow section (SHS) outer and circular hollow section (CHS) inner. A total of 24 specimens were tested under constant axial compressive load and cyclically increasing flexural loading to investigate the structural performance of the composite beam-columns. The test parameters included the axial compressive load level (n), the thickness of the outer stainless steel tube (to), the hollow ratio (χ) and the concrete strength (fcu).The failure modes and hysteresis curves of the concrete-filled double-skin stainless steel tubular (CFDSST) beam-columns have been reported. Based on the test results, the effects of the test parameters on the lateral load (P) versus lateral displacement (Δ) envelope curves, ductility coefficient, dissipated energy and stiffness degradation have been investigated. The results shows that, generally, the axial compressive load level and thickness of outer tubes have a primary influence on the behavior of the test specimens while the hollow ratio and the concrete strength have a little effect when the axial compressive load level is low. Finally, comparisons of initial section flexural stiffness and ultimate bending moments of the beam-columns which were obtained from the tests are made with the predicted ones using the existing design codes and design method.

Numerical modeling on post-local buckling behavior of circular and square concrete-filled steel tubular beam columns

In concrete-filled steel tubular (CFST) beam-columns under cyclic loadings, local buckling of restrained steel tube, crushing and slipping of the confined concrete could have significant influences on strength and stiffness degradation. This paper presents a numerical model based on fiber element discretization for simulating the deterioration behaviour of both rectangular and circular CFST beam columns under axial load and cyclic loading. Uniaxial stress-strain relationships for steel and concrete in CFST beam columns are proposed by introducing unified parameters to control the extent of deterioration. Axial contraction caused by local buckling was accounted by defining an inelastic region that promises plasticity and strength degradation. The numerical model was validated by comparing the simulation results and the associated experimental results. The influences of diameter-to-thickness ratio, concrete and steel strength ranging from normal strength to high strength on the deterioration behavior of circular and rectangular CFST beam-columns were analyzed. Finally, through recognizing the limit state to trigger global strength degradation of a CFST frame, the developed numerical model is applicable for simulating global behavior of CFST frames under collapse-level deformations.

Behavior of thin-walled dodecagonal section double skin concrete-filled steel tubular beam-columns

The behavior of thin-walled dodecagonal section double skin concrete-filled steel tubular beam-columns was investigated in this paper. A series of tests were carried out on specimens having the length of 2000mm. Both outer and inner tubes of test specimens were cold-formed steel dodecagonal hollow sections (DHS). The diameters of outer and inner steel tubes of test specimens were 400mm and 240mm, respectively. Each test specimen was tested to failure, and the behavior under loading was recorded. Finite element model was developed using ABAQUS and verified against the test results. Parametric study was conducted using the verified finite element model. The suitability of current design methods was evaluated.

Energy Dissipation Analysis of Composite Frame Structure with Supplemental Viscous Dampers

With a 10 layer of concrete filled square steel tubular column beam frame structure as the object of study ,discrete structure into multiparticle system and establish a dynamic differential equation,solve this dynamic equation by Newmark -β method .Establish thefinite element model of the structure is based on Sap2000 ,then dynamic elastic-plastic time history analysis are carried out, the research results show that the dynamic characteristics of structure,s story drifts,story shear and acceleration with energy dissipating devices are smaller than the model without energy dissipating devices under different earthquake intensities. the damped effect is considered obvious.

The Finite Element Analysis on the Local Compression of the Concrete Filled Steel Tubular Column-Beam Joint

In order to study the mechanical behavior of the joint between concrete filled steel tubular column and beam with discontinuous column tube at the joint zone under axial pressure, the finite element analysis software ANSYS is adopted for parametric analysis and the analysis results are compared with experimental ones. The principal compressive stress is mainly transmitted by the inside area of the joint which is subjected to local compression if it is low, but extends to more outside areas of the joint if it is high. The radial compressive stress, which is the confined stress of the ring beam to the core concrete of the joint, keeps the same as that the width of the ring beam equal to the diameter of the core area of the joint. The vertical strain on the edge of the joint, which would lead to horizontal annular cracks in the side face of the ring beam, changes from tension in the whole height to tension only in the top part and compression in the lower part of the joint, which is consistent with the experimental phenomenon.