I-section Columns Research Articles

Finite element modelling and design of welded stainless steel I-section columns

Stainless steel is widely used in construction due to its combination of excellent mechanical properties, durability and aesthetics. Towards more sustainable infrastructure, stainless steel is expected be more commonly specified and to feature in more substantial structural applications in the future; this will require larger and typically welded cross-sections. While the structural response of cold-formed stainless steel sections has been extensively studied in the literature, welded sections have received less attention to date. The stability and design of conventionally welded and laser-welded austenitic stainless steel compression members are therefore the focus of the present research. Finite element (FE) models were developed and validated against a total of 59 experiments, covering both conventionally welded and laser-welded columns, for which different residual stress patterns were applied. A subsequent parametric study was carried out, considering a range of cross-section and member geometries. The existing experimental results, together with the numerical data generated herein, were then used to assess the buckling curves given in European, North American and Chinese design standards. Following examination of the data and reliability analysis, new buckling curves were proposed, providing, for the first time, design guidance for laser-welded stainless steel members.

Experimental study of end-plate joints with box columns

Bolted joints between I-section beams and I-section columns have been widely adopted in prefabricated steel frames to avoid field welding, but it is difficult to use bolted beam-to-column joints when box columns are used because of the lack of constructional spaces and the absence of practical design methods. In order to solve this problem, a new end-plate joint form with box columns and I-section beams, as well as three prefabrication techniques for this connection form, are proposed in this paper. Four full-scale specimens were tested: one of the specimens was subjected to monotonic loads, and the other three, constructed with different prefabrication techniques, were subjected to cyclic loads. On the basis of the test results, the resistance, stiffness, rotation capacity, energy dissipation capacity and failure modes of the end-plate joints with box columns were analyzed, and the influences of different prefabrication techniques on the seismic behaviours of the joints were compared. Parametric analysis was conducted with finite element models. The joint specimens prefabricated with different techniques showed similar macro-mechanical properties, and the joint rotations were mainly caused by bulges of the column flanges. All the specimens showed satisfactory deformability and ductility, developing storey drift angles of >0.07rad before initial fractures. The prefabrication techniques notated XW and NW were recommended as preferred because of their superior seismic performance compared to that of the technique notated YW.

Mechanical performance of a new I-section weak-axis column bending connection

This paper reports a novel steel beam-to-column connection suitable for use in the weak axis of I-section column. Monotonic and cyclic loading experimental investigations and numerical analysis of the proposed weak-axis connection were conducted, and the calculation procedure of the beam-column relative rotation angle and plastic rotation angle was developed and described in details. A comparative analysis of mechanical property and steel consumption were employed for the proposed I-section column weak-axis connection and box-section column bending connection. The result showed that no signs of fracturing were observed and the plastic hinge formed reliably in the beam section away from the skin plate under the beam end monotonic loading, and the plastic hinge formed much closer to the skin plate under the beam end cyclic loading. The fracture of welds between diaphragm and skin plate would cause an unstable hysteretic response under the column top horizontal cyclic loading. The proposed weak-axis connection system could not only simplify the design calculation progress when I-section column is adopted in frame structural design but also effectively satisfy the requirements of \'strong joint and weak member\', as well as lower steel consumption.

On modelling of the buckling resistance of welded I-section columns

This paper analyzes the influence of geometrical and material imperfections on the buckling resistance of welded I-section columns subjected to axial compression through numerical and analytical models. The paper is divided into two parts. The first part recalls a FEM parametric study of members under compression taking into account different slenderness ratios, as well as different amplitudes of initial crookedness and different values of postwelding residual stresses. The formulation of analytical approach is the main issue of the second part of the paper. Analytical formulation of the buckling resistance is based on a statistical hypothesis of the minima value approach, called the Marchant-Rankine’s-Murzewski approach (M-R-M). Calibration of imperfection factors included in the analytical formulation is made using the results of FEM simulations performed in the first stage of research investigations.

Compressive buckling strength of extruded aluminium alloy I-section columns with fixed-pinned end conditions

The compressive buckling behaviour of extruded aluminium alloy I-section columns with fixed-pinned end conditions has been experimentally and numerically investigated in this study. A total of 11 column tests, involving two heat-treated aluminium alloys – 6061-T6 and 6063-T5, were carried out to acquire the compressive buckling strengths. Prior to the column tests, material properties of the two aluminium alloys were determined from tensile coupon tests, while the initial local and global geometric imperfections were separately measured by means of experimental techniques. By using the ABAQUS software package, finite element (FE) models that could account for material non-linearity and initial geometric imperfections were developed. The FE models were further validated against the test results, enabling reliable simulation of the compressive buckling behaviour of the tested columns with fixed-pinned end conditions. Based on the obtained test and numerical results, the calculation methods in the current design standards, including the European, Chinese, American and Australian/New Zealand specifications, were all assessed. It was shown that the design provisions in all the four standards provided relatively conservative strength predictions, especially for the aluminium alloys with more pronounced strain hardening capacity.

Experimental investigation and a novel direct strength method for cold-formed built-up I-section columns

This paper aims at investigating the structural response and predicting the ultimate strength of the cold-formed built-up I-section columns affected by local, distortional, global and in particular by the local-distortional (LD) interactive and local-distortional-global (LDG) interactive buckling modes. For this purpose, a total of 18 single C-section columns and 18 built-up I-section columns were tested under uniaxial compression load, respectively. The cross-sectional dimension, the thickness and the length of the tested members were varied in the test so as to cover a wide range of local, distortional and overall slenderness. It was shown in the test that noticeable LD interaction was observed for a built-up column with short length as well as LDG interaction for a built-up column with intermediate length. Due to the clear evidence obtained in the test that LD and LDG interactions cause substantial ultimate strength erosion in cold-formed built-up I-section column, a novel direct strength based method was proposed in this paper to quantify such an erosion effect. The validity of the proposed method was then verified by comparing the results obtained from the proposed method with the test results in this paper as well as several other test results in the literature. The comparison results proved that the proposed method can be used successfully in estimating the ultimate strength of cold-formed built-up I-section column affected by pure buckling mode as well as interactive buckling mode.

Investigation of composite action on seismic performance of weak-axis column bending connections

This paper presents a developed beam-to-column connection which is suitable for weak axis of I-section column and H-shaped beam. Ten cruciform joint specimens, including five bare steel joint specimens (SJ) and five composite joint specimens (CJ) reinforced with partial shear connection, were tested under reversal of loads to evaluate the effect of composite action on the developed weak-axis connections. The beam ends were designed with standard, RBS, cover-plate, taper flange, and welded haunch respectively. The experimental results are analyzed and the composite action is discussed based on the test data. Overall, most joints failed due to welding fracture at the conjunction of diaphragm, skin plate and beam-end flange. But relatively speaking, the composite specimens performed well and achieved the story drift ratios of 0.04rad before experiencing 20% strength degradation because only slight strength degradation occurred in the composite joints compared to bare steel joints, thus the composite joints have a more stable bearing capacity. The test data clearly illustrate that the neutral axis shifted upward significantly under positive bending, resulting in larger strains on beam bottom flange. The reinforcing bars in concrete slab did not work well, but remained in elastic state. The slab slippage was negligible even in 50% degree partial shear connection. The welding quality is an important guarantee to avoid the brittle failure of the connections, and lamellar tearing resistant steel is suggested to be used in skin plate.

Compressive behavior of FRP-confined concrete-encased steel columns

FRP-confined concrete-encased steel I-section columns (FCSCs) are an emerging form of hybrid columns. An FCSC consists of an outer FRP tube, an encased steel section and a concrete infill. The FCSCs possess many advantages over conventional reinforced concrete columns, including the excellent corrosion resistance, excellent ductility and ease for construction. Existing studies on FCSCs, however, have been rather limited. This paper presents a combined experimental and theoretical study on the behavior of FCSCs under concentric and eccentric compression. The experimental program included the testing of a total of 14 specimens, with the main variables being the section configuration, the thickness of the FRP tube and the loading scheme. The theoretical part included the development of a model for section analysis based on the so-called fiber element approach. The test results showed that the buckling of steel section was well constrained and the concrete was effectively confined in FCSCs, leading to a very ductile response under both concentric and eccentric compression. The theoretical model was shown to provide reasonably accurate predictions of the test results.

Estimating the local buckling capacity of structural steel I-section columns at elevated temperatures

This paper presents and analytical study to investigate the local buckling behaviour of structural steel I-section columns at elevated temperatures. An inelastic stability model is developed that accounts for the reduction in stiffness and strength of the steel when subjected to elevated temperatures. Using the model, a comprehensive parametric study is conducted to investigate the effect of each of the parameters of the column. Based on the results of the parametric study, expressions for the local buckling capacity of steel I-section columns are given in which all the parameters are reflected including the interaction between the flange and the web.

Flexural buckling of welded austenitic and duplex stainless steel I-section columns

The paper presents an investigation on welded stainless steel I-section columns. In total, 22 experiments on welded I-section columns, including members buckling about major and minor axis, for both austenitic and duplex stainless steel columns were carried out. Specimen cross-sections and lengths were carefully selected to cover a wide range of geometries and non-dimensional slenderness. Measurements were taken on geometry, global initial geometric imperfection, residual stresses and material properties. The experimental results have been supplemented by the finite element simulation. The resulting structural performance data have been used to assess the applicability of the current design provisions from EN 1993-1-4, ASCE 8-02 and AS/NZS 4673 for the design of stainless steel welded-I sections. Results showed that the design provisions from EN 1993-1-4 and AS/NZS 4673 can be conservatively adopted while the ASCE 8-02 provision shows scattered predictions.

Thermal Buckling Analysis of Axially Loaded Columns of Thin-Walled Open Section with Nonuniform Sectional Properties

This paper presents an analytical study on the thermal buckling analysis of axially loaded columns of thin-walled open section with nonuniform sectional properties. Obtained herein are critical loads related to flexural, torsional and flexural-torsional buckling of an I-section column subjected to an axial compressive load applied at the geometric centroid, and under linearly varied non-uniform temperature distribution scenarios. The analysis is accomplished using traditional energy methods. The influences of thermal strain, nonuniform distribution of pre-buckling stresses, and variation of pre-buckling stresses along the longitudinal axis of the column on critical buckling loads are examined. The present results highlight the importance of nonuniform sectional properties in the buckling analysis of columns of doubly symmetric section.

Local–overall interactive buckling behaviour of welded stainless steel I-section columns

The local–overall interactive buckling behaviour of welded stainless steel I-section columns was experimentally and numerically examined in this study. A total of ten test specimens were fabricated from hot-rolled stainless steel plates and axially loaded between two pin-ended supports. The specimens failed by local–overall interactive buckling about the minor axis. Prior to the member testing, material properties, residual stresses and initial local and global geometric imperfections were all accurately determined. Detailed finite element (FE) models, capable of simulating the interactive buckling behaviour and predicting the ultimate capacity of welded stainless steel I-section columns, were validated against the obtained test results. The validated FE models were subsequently used to carry out systematic parametric studies, exploring the influences of the key input parameters, including the welding residual stresses, initial geometric imperfections, material properties and slenderness ratios. The generated test and numerical results were then used to assess the accuracy of a series of existing design methods: Eurocode 3 Part 1.4 and the design proposal of Rasmussen and Rondal, both of which employ the effective width concept, and the two separate design proposals of Becque et al. in the EN 1993-1-4 and AS/NZS 4673 formats and the proposal of Huang and Young, all of which are based on the direct strength method (DSM). Based upon the assembled data points, two separate design curves are proposed herein for austenitic and duplex stainless steels, which have been demonstrated to offer very accurate strength predictions for welded stainless steel I-section columns undergoing interactive buckling.

Experimental research on behavior of 460 MPa high strength steel I-section columns under cyclic loading

To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.

Local-Overall Flexural Interaction of Pinned-Ended Thin-Walled I-Section Columns

The structural performance of thin-walled compression members are subject to the effects of local buckling, interaction between buckling modes, loading end conditions and material yielding and that due to these effects the compressive carrying capability of thin-walled members can be significantly diminished. This paper employs the finite element simulation to examine the local-overall flexural interaction response of pinned-ended thin-walled I-section columns that covers the complete compressed loading history from the onset of elastic local buckling through the nonlinear elastic and elasto-plastic post-buckling interactive phases of behaviour to final collapse and unloading. A detailed account of the growth and redistribution of stresses on the surfaces is given in the paper. Pinned-ended conditions means, of course, simply supported conditions at the column ends with respect to global rotations and the ends of the constituent plates of the cross-section can be treated as either locally rotationally constrained or locally rotationally free. The numerical simulations take into account the influence of material nonlinearity and geometrical imperfections on the compressive ultimate failures of the sections, however, the study is limited to the interaction of local buckling with overall flexural bending as well as locally rotationally constrained condition. This paper shows that the ultimate failure of the columns is related with yielding on the compression sides of the outer surfaces of the section walls at the web, flanges and section junctions mostly located along the length of the columns.

Experimental and numerical study on the structural behavior of eccentrically loaded GFRP columns

Glass fiber reinforced polymer (GFRP) pultruded profiles are being increasingly used in civil engineering applications. Although they offer several advantages over traditional materials, such as high strength, lightness and non-corrodibility, GFRP profiles present low elasticity and shear moduli, which together with their slender walls makes them very prone to buckling phenomena. Several previous studies addressed the global and local buckling behavior of GFRP pultruded members under concentric loading. However, little attention has been given to the effect of small eccentricities, which may arise from material geometrical imperfections or construction errors. This paper presents results of experimental and numerical investigations about the structural behavior of GFRP pultruded columns subjected to small eccentric loading about the major (strong) axis. To accomplish such goal, three series of 1.50m long GFRP I-section (120×60×6mm) columns were tested in compression applied with the three following eccentricity/height of the cross-section ratios: e/h=0.00, 0.15 and 0.30. It was found that such small eccentricities are of major importance for the behavior of GFRP pultruded columns. Although the initial axial stiffness of eccentrically loaded columns was similar to that of concentrically loaded ones, for increasing loads the stiffness considerably decreased due to bowing and second-order P–δ effects. Furthermore, results show that the load capacity of columns subjected to loads applied within the kern boundaries is reduced up to 40% at an approximately linear trend. Results obtained from the experimental campaign were compared with analytical predictions and numerical simulations using (i) the finite element method (FEM) and (ii) the generalized beam theory (GBT). In general, a very good agreement was obtained between experimental data and analytical and numerical results.

The Static Stability Analysis of Single-Story Steel Frames with I-Section Columns

Static stability analysis to 12 kinds single-story steel frames with I-section columns is analyzed based upon bilinear lateral force versus displacement framework curve and finite element method, then ultimate displacements are obtained. In comparison, the framework curves and ultimate displacement calculated by modified stiffness and cross-section plastic moment theory accord with that calculated by finite element method. This provides the referential basis for the static stability analysis to a single-story steel frame.

Tests and numerical study of ultra-high strength steel columns with end restraints

High strength steels with the nominal yield strength more than 460 MPa have begun to be applied in the construction of many steel structures, but there are short of sound researches on the major axis buckling behavior of such steel welded I-section columns, especially for the ultra-high strength steels having the nominal yield strength more than 690 MPa. In this paper, the experimental research is described on the overall buckling behavior about the major axis of ultra-high strength steel compression I-section columns with end restraints. In this research 8 columns made from 2 kinds of ultra-high strength structural steels S690 and S960, with nominal yield strengths of 690 MPa and 960 MPa, respectively, were tested. Based on the test results, the finite element analysis (FEA) model was validated to analyze this behavior of ultra-high strength steel columns, and the buckling strength of pin-ended columns fabricated from such steels were calculated by the verified FEA model, which were compared with the design buckling strengths according to the Eurocode 3, the American specification for structural steel buildings ANSI/AISC 360–05, and the Chinese codes for steel structures design GB50017-2003 respectively. It shows that the major axis nondimensional buckling strengths of the ultra-high strength steel compression columns, whose buckling curve is type b according to Eurocode 3 and GB50017-2003, are much higher than that calculated according to the column curve b, even higher than the curve a 0 in Eurocode 3 and the curve a in GB50017-2003 on average, and they are also higher than the design values according to ANSI/AISC 360–05. It is therefore indicated that the buckling strength about the major axis of the ultra-high strength steel I-section columns is improved a lot compared with the ordinary strength steel columns on a non-dimensional basis, and the column curve a 0 and curve a can be adopted to design this behavior in Eurocode 3 and GB50017-2003, respectively. Besides, there is no obvious difference between the major axis nondimensional buckling strengths of the pin-ended I-section columns fabricated from these two kinds of ultra-high strength steels: S690 and S960. These research works will provide the test basis to complete the buckling design method and theory of the ultra-high strength steel columns, and also be helpful for the application of ultra-high strength steel structures.

Non-linear GBT formulation for open-section thin-walled members with arbitrary support conditions

This paper presents the development and illustrates the application of a beam finite element based on Generalised Beam Theory (GBT) and intended to analyse the elastic post-buckling behaviour of thin-walled steel members exhibiting arbitrary open cross-section and with non-standard support conditions ( e.g., in-span bracing systems). After briefly reviewing the main concepts and procedures required to obtain the GBT system of non-linear equilibrium equations, the paper describes the steps involved in the numerical implementation (incremental–iterative strategy) of a non-linear beam finite element that incorporates the influence of the non-standard support conditions. Finally, the application and capabilities of the proposed GBT-based beam finite element are illustrated by means of the presentation and discussion of numerical results concerning the post-buckling behaviour of lipped I-section columns and lipped channel columns and beams with and without localised displacement restraints. For validation purposes, most GBT-based results are compared with values yielded by shell finite element analyses carried out in the commercial code A nsys.

Finite Element Analysis on the Local Buckling Behavior of High Strength Steel Members under Axial Compression

Compared to the ordinary strength steel extensively applied in structures currently, high strength steel, a new kind of construction material, has many differences on mechanical properties. Though high strength steel has been applied in several projects in the world, which has obtained good effects, there is a lack of the design method for high strength steel structures and researches on the loading capacity of high strength steel members. To study the local buckling behavior of high strength steel members under axial compression, finite element models are developed to predict the loading capacity of high strength steel welded I-section and box-section stub columns under axial compression in this paper. With accurate simulation of 17 high strength steel specimens, the finite element analysis results agree well with the corresponding test results, and the average deviation of the ultimate loading capacity of 17 specimens is about -3.1%. It’s verified that the finite element models developed in this paper can accurately simulate high strength steel members with the initial geometric imperfections and residual stresses, and analyze the local buckling behavior of high strength steel members under axial compression. In addition, it provides a basis for the parametric study of high strength steel members under axial compression in future.

Experimental investigation and design of aluminum columns with longitudinal welds

This paper presents an experimental investigation of longitudinally welded aluminum alloy I-section columns subjected to pure axial compression. The specimens were fabricated using 6061-T6 heat-treated aluminum alloy. The test program included 20 column tests which were separated into 2 test series of different types of welding sections. Each test series contained 10 columns. All the specimens were welded using the Tungsten Inert Gas welding method. The length of the specimens ranged from 442 to 2433 mm in order to obtain a column curve for each test series. The observed failure mode for the column tests includes mainly flexural buckling around the minor axis and the major axis by applying support except for one column (ZP1217-1) which buckled in the local zone and some columns which failed in the weld. The test strengths were compared with the design strengths predicted by the European Code and China Code for aluminum structures. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section columns, and to check the accuracy of the design rules in the current specifications.