Lateral Distortional Buckling Research Articles

Lateral Buckling Strengths of Cold-Formed Channel Section Beams

This paper is concerned with the inelastic lateral buckling strengths of cold-formed channel section (CFC) beams. Code rules for designing steel beams against lateral buckling that are based on data for hot-rolled I-section beams may be unsuitable for CFC beams, because they have different stress-strain curves, residual stresses, and initial imperfections. Distortion may reduce the resistance of a CFC beam to lateral buckling. In addition, because of the monosymmetry of the cross section, the effective shear center moves toward the web and the effective section becomes asymmetrical after yielding, so that a CFC beam under major axis bending is subjected to minor axis bending and twisting. Also, the minor axis bending and warping strain distributions, and therefore the strengths of CFC beams, are related to the twist rotation and minor axis deflection directions. This paper deals with these problems by developing an advanced finite element model to investigate the elastic lateral-distortional buckling, inelastic behavior, and strengths of CFC beams with residual stresses and initial imperfections. The results are used to develop improved design rules for CFC beams. The effects of moment distribution and load height on the strengths are also studied.

A simplified distortional buckling model for doubly symmetrical I-sections

Lateral torsional instability of I-beams considers the relative displacement of the unstable compression flange to the stable tension flange. It is commonly assumed that little or no distortion takes place between the two flanges. In this paper, an approach is proposed whereby the section properties that control lateral torsional buckling are adjusted to allow for the influence of cross-section distortion, by the use of simple spring models representing the relative stiffness of the flanges and the web. The model is developed for elastic, inelastic, and plastic cases and compared with the results obtained from finite element models developed by other researchers. A method of quantifying the lateral distortional buckling resistance of I-beams is of particular importance in the hogging moment region of continuous composite beams; the ability of the proposed model to deal with this complex problem has been previously demonstrated by the authors. In this paper, the proposed model is used to illustrate the influence of distortional buckling on doubly symmetrical I-sections.Key words: lateral, distortional, I-beams, elastic, inelastic.

Analytical and Experimental Study of Lateral and Distortional Buckling of FRP Wide-Flange Beams

A combined analytical and experimental evaluation of flexural-torsional and lateral-distortional buckling of fiber-reinforced plastic (FRP) composite wide-flange (WF) beams is presented. Based on e...

Buckling Experiments on Hollow Flange Beams with Web Stiffeners

The hollow flange beam (HFB) is a new cold-formed and resistance-welded section developed in Australia. Due to its unique geometry comprising two stiff triangular flanges and a slender web, the HFB is susceptible to a lateral-distortional buckling mode of failure involving web distortion. Investigation using finite-element analyses showed that the use of transverse web plate stiffeners effectively eliminated lateral-distortional buckling of HFBs and thus any associated reduction in flexural capacity. A detailed experimental investigation was then carried out to validate the results from the finite-element analysis and to improve the stiffener configuration further. This led to the development of a special stiffener that is screw-fastened to the flanges on alternate sides of the web. This paper presents the details of the experimental investigation, the results, and the final stiffener arrangement whereas the details of the finite-element analyses are presented in a companion paper.

Lateral-Distortional Buckling of Hollow Flange Beams

While the flanges of cold-formed hollow flange beams (HFBs) are very stiff torsionally, their webs are comparatively flexible, and may allow web distortion effects to reduce their resistances to lateral buckling. There is no simple formulation for predicting the effects of web distortion on the lateral buckling of HFBs. As a result, structural designers are unable either to check or to extend the available elastic buckling predictions; thus code writers are not able to provide explicit formulations for the effects of distortion. The conversion from elastic buckling to strength for HFBs is also questionable, since cold-formed beams have different stress-strain curves, residual stresses, and geometrical imperfections from those of hot-formed beams. This paper deals with these problems, first by finding a simple but sufficiently accurate closed-form solution for the effects of distortion on the elastic lateral buckling of simply supported HFBs in uniform bending, and then by developing an advanced theoretical method of predicting the effects of the stress-strain curve, residual stresses, and geometrical imperfections on the strengths of HFBs that fail by lateral-distortional buckling. Such a method allows the development of a conversion from elastic buckling to strength, which is appropriate for HFBs. The use of this conversion together with the simple approximation developed here for elastic lateral-distortional buckling provides a rational basis for the lateral buckling design of unbraced HFBs.

Elastic distortional buckling of tapered composite beams

The overall buckling mode in a composite steel-concrete beam over an internal support is necessarily lateral-distortional, in which the bottom compressive range displaces laterally and twists, since the top flange is restrained by the nearly rigid concrete slab. An efficient finite element method is used to study elastic lateral-distortional buckling in composite beams whose steel portion is tapered. The simplified model for a continuous beam that is presented herein is a fixed ended cantilever whose steel portion is tapered, and is subjected to moment gradient, This is intended to give an insight into distortion in a continuous beam that occurs in the negative bending region, and the differences between the cantilever representation and the continuous beam are highlighted. An eigenproblem is established, and the buckling modes and loads are determined in the elastic range of structural response. It is found from the finite element study that the buckling moment may be enhanced significantly by using a vertical stiffener in the region where the lateral movement of the bottom range is greatest. This enhancement is quantified in the paper.

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.

Lateral Distortional Buckling of Monosymmetric Beams under Point Load

Based on a new expression for the work done due to buckling, a computationally efficient method is presented for the lateral distortional buckling of monosymmetric beams. The method requires a knowledge of the stress distribution in the beam. For a simply supported monosymmetric beam subjected to a concentrated vertical load, a simplified stress distribution is assumed and the Rayleigh-Ritz method is used to analyze the lateral distortional buckling behavior. When distortion of the web is suppressed, the present approach agrees with the classical energy methods. However, for short beams and for concentrated loads, web distortion becomes important and the classical methods seriously overestimate the critical load. Other methods that have allowed for web distortion have been limited to end moments (or a cantilever), whereas this method can deal with any type of load including concentrated loads. The accuracy of the method is verified by results obtained from ABAQUS.

Lateral distortional buckling of monosymmetric I-beams under distributed vertical load

An energy method is developed for analyzing the lateral buckling behaviour of beams subjected to distributed vertical load, with full allowance for distortion of the web. The paper presents a simple method which uses nonlinear elastic theory to obtain the external work due to buckling, and which obtains a new formulation of total potential energy for a monosymmetric I-beam. The method is validated by comparison with the classical energy methods when distortion of the web is suppressed (rigid web case). For both uniform distributed load and end moments the solution matches the critical lateral load obtained from the classical energy equations. For the case when the web is flexible, a 5th order polynomial shape function is used to describe the web buckling shape. The accuracy of the method is verified by results obtained from ABA QUS. The paper shows that for short beams the classical method seriously overestimates the critical load.

Lateral torsional and distortional buckling of channel- and hat-sections

Abstract For thin-walled sections, lateral and lateral-torsional buckling are often affected by distortion of the section and this can severely reduce the critical stress. A calculation method for the critical stress which takes account of distortional effects, based on Generalised Beam Theory (GBT), is presented in this paper. The limiting slenderness at which distortional effects begin to take effect is evaluated for channel- and hat-sections on the basis of parametric studies. Approximate formulae for the limiting slenderness are then given.

Lateral-Distortional buckling of steel I—Section members

Abstract The usual types of buckling of steel members assumed in design are lateral-torsional and local buckling modes. In lateral-torsional buckling, the cross-sections of the member translate and twist as rigid bodies. On the other hand, local buckling is characterized by localised distortions of the cross-section over a short wavelength in the absence of lateral translation. These two modes are really limiting buckling types for short members (local buckling) and for long members (lateral-torsional buckling). For intermediate length members, the two modes interact to produce a lateral-distortional buckle, characterised by simultaneous distortion and lateral deflection of the cross-section. During the past 15 years or so, a proliferation of research work has been undertaken in Australia to quantify the effects of lateral-distortional buckling. The paper provides a survey of this research, and concludes with recommendations regarding the relevance of lateral-distortional buckling to design situations.

Distortional Buckling Solutions for Continuous Composite Beams

The paper presents a theoretical analysis of fixed-ended composite steel-concrete beams, representative of members continuous over an internal support. The analysis is elastic, and allows for the variation of sagging and hogging bending along the member. The stress resultants obtained from the virtual work analysis are used for an extensive finite element study of lateral-distortional buckling of fixed-ended composite beams. The details of the computer program adopted are described elsewhere. Based on the elastic buckling solutions, a design method is proposed to calculate the strength of the composite beam with respect to the buckling limit state. This design method is less conservative than that implied in current design codes, and leads to economies of material. The analysis for continuous composite beams provides a benchmark study for future studies.

Closure to “ Lateral Distortional Buckling: Predicting Elastic Critical Stress ” by P. Goltermann and S. E. Svensson (july, 1988, Vol. 114, No. 7)

Closure to “ <i>Lateral Distortional Buckling: Predicting Elastic Critical Stress</i> ” by P. Goltermann and S. E. Svensson (july, 1988, Vol. 114, No. 7)

Discussion of “ Lateral Distortional Buckling: Predicting Elastic Critical Stress ” by P. Goltermann and S. E. Svensson (july, 1988, Vol. 114, No. 7)

Discussion of “ <i>Lateral Distortional Buckling: Predicting Elastic Critical Stress</i> ” by P. Goltermann and S. E. Svensson (july, 1988, Vol. 114, No. 7)

Lateral-distortional buckling of tee-section beams

A fine element method that incorporates plate behaviour is developed for modelling the lateral-distortional buckling of tee-section beams. The method is shown to agree well with independent buckling results for tee-beams. Since relatively few elements are needed to obtain satisfactory convergence, the method is efficient computationally. The finite element analysis is used to study the elastic distortional buckling of tee-beams of practical geometry under moment gradient. The disparities found between the elastic flexural-torsional and distortional buckling moments are discussed.

Lateral Distortional Buckling: Predicting Elastic Critical Stress

The problem of restrained lateral beam buckling is being treated in this paper. The restraint represents complete lateral and arbitrary continuous rotational restraint of one flange, the latter is represented by the spring stiffness C0. A simple theory, in which the problem is transformed into an ordinary fourth order differential eigenvalue problem is presented and design‐tables are given. It refines a method previously developed by Svensson. The results obtained are compared with exact results for C0=0 (the classical theory) and C0=∞ the latter based on results given in the published literature. For C0=0 a maximum deviation of 1% and for C0= deviations in the range of 1% to 4% were found. The results also confirm that a method proposed by other researchers yields similar good results. It is concluded that the method developed in the present paper, due to its generality and simplicity, provides an accurate and quick method for solving complex lateral distortional buckling problems.