I-section Columns Research Articles

Research on Stability of High Strength Aluminum Alloy Columns Loaded by Axial Compressive Load

This paper reports experimental study of 17 high strength aluminium alloy specimens of type of 6082-T6 under axially compressed load including I-section column, rectangular hollow section. The general-purpose non-linear finite element analysis software ABAQUS is adopted to simulate the mechanical performance and overall buckling of aluminium alloy columns. The feasibility of finite element method has been verified through the comparison between the simulation results and the test finding. Finally, based on the experimental data and numerical calculation results, a useful column curve formulation to calculate the coefficient of stability of 6082-T6 aluminium alloy columns loaded by axial compressive load is derived. Comparison between column curves from proposed formulation and different code and test results has been presented, from which the validation of the proposed formulation has been verified.

Performance Enhancement of Steel Columns Using Concrete-Filled Composite Jackets

This paper studies the cross-sectional behavior of steel columns strengthened with fiber-reinforced polymers (FRPs). The composite column is constructed by wrapping the steel I-section column with epoxy-saturated glass- and carbon-FRPs (GFRP and CFRP) sheets in the transverse direction and subsequently filling the voids between the FRP and the steel with concrete. Experimental tests were performed on stub columns under axial compression including one to three CFRP wraps. A corner treatment technique, to avoid stress concentration at the corners and to improve confinement efficiency, was also investigated. A simplified analytical model was developed to predict the axial behavior of the composite columns. Experimental results showed significant enhancement in the behavior of the composite columns primarily attributable to the confinement mechanism imposed by the FRP jacket and concrete. Increasing the corner radius resulted in higher compressive strength of the confined concrete and ultimate axial strain of the composite columns. Good agreement between the analytically developed axial load-displacement relationships and the test data indicates that the model can closely simulate the cross-sectional behavior of the composite columns.

GBT formulation to analyse the buckling behaviour of FRP composite open-section thin-walled columns

Abstract This paper presents a Generalised Beam Theory (GBT) formulation to analyse the local and global buckling behaviour of FRP (fibre-reinforced polymer) composite thin-walled columns with arbitrary open cross-sections, which takes into account both shear deformation and cross-section deformation effects. After describing the steps and procedures involved in performing the GBT cross-section analysis of an arbitrarily branched composite (laminate plate) thin-walled member, the paper addresses the numerical implementation of the proposed GBT formulation, carried out by means of the finite element method (GBT-based beam element) – particular attention is devoted to the derivation of the element linear and geometric stiffness matrices, which incorporate all the material coupling effects. In order to illustrate the application and capabilities of the proposed formulation and implementation, several numerical results are presented and discussed, dealing with the local and global buckling behaviour of FRP composite I-section columns with different ply orientations and stacking sequences. Taking advantage of the GBT modal features, deep insight is acquired on the complex composite member buckling mechanics, namely those involving bending–torsion or global–local coupling effects. In particular, one investigates the influence of (i) the constitutive assumption regarding the transverse extension occurring in the cross-section composite walls and (ii) the distribution of pre-buckling normal stresses (due to axial compression) on the buckling behaviour of I-section columns. For validation purposes, the above results are compared with values recently reported in the literature and estimates obtained from shell finite element analyses.

Design of high strength steel columns at elevated temperatures

The main objective of this paper is to study the behaviour and design of high strength steel columns at elevated temperatures using finite element analysis. In this study, equations predicting the yield strength and elastic modulus of high strength steel and mild steel at elevated temperatures are proposed. In addition, stress–strain curve model for high strength steel and mild steel materials at elevated temperatures is also proposed. The numerical analysis was performed on high strength steel columns over a range of column lengths for various temperatures. The nonlinear finite element model was verified against experimental results of columns at normal room and elevated temperatures. The effects of initial local and overall geometrical imperfections have been taken into consideration in the analysis. The material properties and stress–strain curves at elevated temperatures used in the finite element model were obtained from the proposed equations based on the material tests. Two series of box and I-section columns were studied using the finite element analysis to investigate the strength and behaviour of high strength steel columns at elevated temperatures. Both fixed-ended stub columns and pin-ended slender columns were considered. The column strengths predicted from the finite element analysis were compared with the design strengths predicted using the American, European and Australian specifications for hot-rolled steel columns at elevated temperatures by substituting the reduced material properties. In addition, the direct strength method, which was developed for the design of cold-formed steel columns at normal room temperature, was also used in this study to predict the high strength steel column strengths at elevated temperatures. The suitability of these design rules for high strength steel columns at elevated temperatures is assessed. Generally, it is shown that the American and European specifications as well as the direct strength method conservatively predicted the column strengths of high strength steel at elevated temperatures. The European Code predictions are slightly more conservative than the American Specification and the direct strength method predictions.

Post local buckling strength of bi-axially loaded slender I-section columns

Slender section columns can carry additional loads up to failure after local buckling has happened in its elements. This post-local buckling capacity depends mainly on the width–thickness ratios of elements forming the section as well as the state of stresses within it. This paper presents tests to examine the influence of these factors on this additional capacity. The experimental local buckling and ultimate loads of two series of specimens are presented. Each series contains a group of slender I-sections varying in their flange and web width–thickness ratios. In the first series the loads are applied axially through the CG. of the sections, while in the other one they are applied eccentrically about the major and minor axis. Additionally, the tested specimens are simulated numerically by a non-linear finite element model considering different values of overall geometric imperfections. Generally, the post-local buckling strength gained by the sections is higher for axially loaded columns than that of bi-axially loaded ones, and it decreases with increasing eccentricity for the same web and flange width–thickness ratios.

Spatial stability of braced thin-walled members of steel structures

Abstract The solutions of the spatial stability problems for: (1) monosymmetrical columns and beams with a prescribed axis of rotation, compressed and bent under transverse loading and (2) monosymmetrical beams with a horizontal (lateral) brace, loaded with an arbitrary number of concentrated forces are provided. The considered structural members were additionally point braced along their length to prevent them from twisting and warping. The spatial stability problems were formulated as distributional differential equations, which were solved approximately using the Bubnov–Galerkin orthogonalization method and then the solutions of the problems were derived for the structural members for different support conditions at their ends. The general solutions were reduced to eigenvalue problems. The numerical calculations can be performed using in-house computer programs. Each of the considered problems is illustrated by numerical examples and ready-made particular solutions. In the case of the beams with a lateral brace, also the effect of stiffeners on the lateral buckling load was examined. The theoretical solutions have been validated by model tests carried out on laterally and longitudinally braced steel I-section columns subjected to compression and bending and on longitudinally braced steel I-beams.

Post-Buckling of Composite I-Sections. Part 2: Experimental Validation

An experimental investigation was conducted in order to verify the theoretical model described in Part 1 as well as to obtain experimental insight and to generate a database for the post-buckling behavior of composite I-sections. The experiments were performed using a combination of the shadow moiré technique, strain gages, LVDTs (linear variable differential transformer), and dial gages. A total of twenty carbon-fiber/epoxy I-section columns were manufactured and tested with seven specimens from woven fabric and thirteen from unidirectional (UD) tape. The initial buckling load, lateral deflection of the web and flange as well as the crippling load were measured. The experimental results were compared with those of the theoretical model described in Part 1. Agood agreement was observed.

Post-Buckling of Composite I-Sections. Part 2: Experimental Validation

An experimental investigation was conducted in order to verify the theoretical model described in Part 1 as well as to obtain experimental insight and to generate a database for the post-buckling behavior of composite I-sections. The experiments were performed using a combination of the shadow moire technique, strain gages, LVDTs (linear variable differential transformer), and dial gages. A total of twenty carbon-fiber/epoxy I-section columns were manufactured and tested with seven specimens from woven fabric and thirteen from unidirectional (UD) tape. The initial buckling load, lateral deflection of the web and flange as well as the crippling load were measured. The experimental results were compared with those of the theoretical model described in Part 1. Agood agreement was observed.

Lateral-distortional buckling of continuously restrained columns

A rational model for predicting the elastic buckling load of thin-walled Isection columns, restrained fully against translation and elastically against twist at one flange, is presented. The energy method used results in a third-order eigenproblem. The numerical method is illustrated by considering the elastic buckling of doubly-symmetric and monosymmetric columns with various degrees of elastic twist restraint. It is shown that the buckling mode is of a lateral-distortional type. The accuracy of the U -frame buckling model used in through girders for predicting the lateral-distortional buckling load is assessed in the study.

The strength of stainless steel built-up I-section columns

The findings of an investigation into the structural performance of stainless steel built-up I-section columns are presented. The stainless steel used in this study is a modified AISI Type 409 stainless steel designated 3CR12, a corrosion-resisting steel. Due to the gradual yielding properties of Type 3CR12 corrosion-resisting steel, column strength is best predicted by using the tangent modulus approach. The influence of residual stresses on column strength can be included in the tangent modulus formulation by using the mechanical properties of stub column tests instead of the mechanical properties of the virgin plates.

Tests of high strength steel columns

The paper describes a test programme on columns fabricated from high strength steel plates with nominal yield stress of 690 MPa. The programme comprised 13 box and I-section specimens, including fixed-ended stub columns and pin-ended long columns. For the pin-ended columns, two tests were performed for each length using eccentric and concentric axial loading. The purpose of the test programme was to select a curve for high strength steel columns with a nominal yield stress of 690 MPa from the multiple column curves used in the Australian steel structures standard. It is shown that the α b = −0·5 curve is the appropriate curve for box and I-section columns fabricated from flame-cut high strength steel plate with a nominal yield stress of 690 MPa. This curve is higher than the α b = 0 curve for box and I-section columns fabricated from ordinary steel because the effect of residual stresses is less detrimental to the strength of high strength steel columns than to the strength of ordinary steel columns. The paper also shows a comparison of the tests with column design strengths of the Australian steel structures standard AS4100, the Load and Resistance Factor Design Specification of the American Institute of Steel Construction, The British Standard BS5950: Part 1, and the draft European Committee for Standardisation (CEN) Eurocode3. The design strengths are shown to be in close agreement with the tests except for Eurocode3 which conservatively predicts the test strengths.

Compression Tests of Long Welded I‐section Columns

The results of compression tests of long, welded I-section columns composed of slender plates of high tensile steel are described. Tests of concentrically loaded specimens are compared with a finite strip nonlinear analysis model for predicting the elastic interaction of local and overall buckling of thin-walled columns. Tests of concentrically and eccentrically loaded specimens are compared with a finite strip nonlinear analysis model for predicting the elastic interaction of local and overall buckling of thin-walled columns. Tests of concentrically and eccentrically loaded specimens are compared with the proposed AISC Load and cross sections. The column strengths are also compared with those of compact columns of equivalent weight to demonstrate the economies available for columns with slender cross sections.

Restrained composite columns in uniaxial bending

Abstract The strength and behaviour of about 250 encased I-section columns, braced against sidesway and under uniaxial bending, have been presented. The cases studied cover the practical range of end eccentricity, stiffness of rotational end restrains (assumed elastic), slenderness and concrete cover, and include symetrical as well as asymmetrical arrangements of eccentricities and restraints, and major and minor axis bending cases. The columns are analysed by computer using a new iterative technique based on Newmark's integration procedure. Typical curves are presented showing the variation with load of the support and maximum moments, central deflection and strains at critical section. In almost all cases the peak load is reached when material failure occurs. The failure loads for columns under asymmetrical bending and with large effective end eccentricity are found to increase with slenderness, contrary to expectation. Because of material non-linearity, support moments in slender columns become negative at failure and moments throughout the length of certain short columns reverse. The paper also discusses the likely error in the computed strength due to the assumption of reversibility of the materials stress-strain curves.

Nonlinear Analysis of Thin Sections in Compression

The finite strip method developed by Cheung is extended to include the nonlinear response of imperfect plate strips under axial compression. Local buckling and postbuckling phenomena are included in the formulation. The convergence and accuracy of the method is tested against accepted solutions for uniformly compressed plates with different boundary conditions. Studies are made of the nonlinear response of box and I-section columns. The application of the method to the interaction of local and Euler buckling of straight columns with imperfect plates is presented.

Interaction Buckling in I-Section Columns

The interaction between local and Euler buckling in an imperfect I-section column produces an adverse effect on its strength. Analytical models based on the effective section method and the finite strip method which account for interaction buckling are compared with tests performed by Kalyanaraman, Pekoz, and Winter (1977). A design method based on the SSRC column curves is proposed to account for the effects of interaction buckling in I-section columns. This design method is also compared with the tests.

Stability of columns supported laterally by side-rails

The buckling conditions are derived for an I-section column supported laterally by uniformly spaced side-rails which provide rigid lateral support and elastic torsional restraint, the column being subjected to any combinations of axial load and uniform or non-uniform moment about the major axis. Criteria are developed to determine, for any loading condition and given spacing of lateral supports, the minimum torsional restraint which causes buckling to occur between supports rather than in an overall mode.

The effect of cross-section shape on the creep buckling behaviour of columns

The creep buckling phenomenon studied by Hoff for slender columns whose stress (σ)/strain rate ( ϵ ˙ ) law is (1) ϵ ˙ = B σ n is discussed. It is shown, in particular, that the “critical time” for a given loaded column (i.e. the time taken for the column to collapse) may be considered to depend upon three separate factors: (i) the initial “eccentricity” of the column, (ii) the “small deflexion” behaviour of the column, characterized by a constant “doubling time”, and (iii) a lateral deflexion ( ȳ ) which is a function of the column cross-section geometry and the value of n for the material. The study of (i) is beyond the scope of this paper. Factor (ii) is readily ascertained, as it involves a linearization of the material stress/strain rate law (1). The dependence of factor (iii), ȳ , on the relevant variables is studied in the paper by means of a set of numerical calculations of tho deflexions of a single-parameter column. A simple empirical formula is deduced, which appears to givo a reasonably close, and “safe’, value of ȳ for any symmetrical cross-section; the value of ȳ may then be used in a simple way to estimate the lifetime of the column. A particular result is that an “equivalent” idealized I-section column invariably has a shorter life than the actual column to which it corresponds, when n >2.

Lateral Buckling of Eccentrically Loaded I-Section Columns

Lateral Buckling of Eccentrically Loaded I-Section Columns

Lateral Buckling of I-Section Column With Eccentric End Loads in Plane of the Web

Abstract When a relatively slender column of the symmetrical I or WF shape is loaded eccentrically in the plane of the web by longitudinal end loads it may fail by elastic instability involving a combination of lateral bending and twisting. Timoshenko has shown that in the case of the solid rectangle a considerable end eccentricity causes the critical buckling load to be only slightly less than the Euler critical load for the same strip loaded axially. The corresponding solution for the WF or I-column, presented herein, shows that relatively small eccentricities of the longitudinal end load applied in the plane of the web cause a large falling off from the Euler critical load. For the ideally straight column, with a material perfectly elastic up to the yield point, there would be a critical l/r ratio for any given eccentricity, column length, and material. Below this critical ratio the column would fail by yielding, according to the secant or eccentricity formula. Above the critical ratio the failure would be by elastic instability with respect to lateral bending and twisting. Application of the equations is made to two structural wide-flange sections, of light and medium weight, and the results are presented in the form of diagrams.