Australian AS4100 Research Articles

Moment modification factors for the buckling design of steel beams – new recommendations

When a unbraced flexural steel beam is subjected to a ununiform moment distribution, a simplified moment modification factor (denoted as Cb) should be evaluated for the design of the buckling resistance of that member. However, typical standards for the buckling design of steel structures (e.g., American AISC A360, Australian AS-4100, Canadian CSA S16, Eurocode 3 and Japanese standards) currently recommend different design equations for the factor. Also, such equations are based on simplified expressions those are not exact solutions. Thus, the present study firstly revise the standard equations to discuss their advantages and disadvantages in application. Also, a numerical solution based on a finite element analysis package is then conducted in the present study to predict the Cb factor. The numerical solution is successfully validated against available research results. Based on the comparison of the modification factors between of the present numerical study and those based on the design standards, it is observed that the modification factors based on the current design standards maybe not safety enough to predict the buckling resistances in several loading cases. The present study finally recommends a new modification more on the safe side for the Cb factor to ensure a conservative design

Buckling of welded high-strength steel I-beams

National constructional steel design standards preclude many high-strength quenched and tempered steel grades, and with the growth update of such steels in structural applications, revision or new guidance is needed. This paper reports experiments and presents numerical studies of welded high-strength steel (HSS) I-section beams fabricated by welding BISPLATE-80 (nominal yield stress fy = 690 MPa) and BISPLATE-100 (fy = 890 MPa) plates. For the experimental program, three BISPLATE-80 and five BISPLATE-100 I-sections were fabricated and tested under scenarios of uniform bending and moment gradient. The specimens were designed to develop either lateral-torsional or local buckling modes, with tensile fracture not being observed during the tests. The buckling capacity so obtained significantly exceeded the predictions of Eurocode 3 and of the Australian AS4100, especially for intermediate beam slendernesses, while the ANSI/AISC 360–16 guidelines marginally estimated the buckling resistance of specimens. It was also found that lateral-torsional buckling initiated after partial yielding of the compression flange. The numerical studies consisted of two ABAQUS finite element (FE) models, being a test simulation model as well as a generic representation, to facilitate extending the pool of experimental data, which showed that Eurocode 3 and AS4100 underestimate the buckling strength of intermediate and slender beams, while the ANSI/AISC 360–16 curves overestimate the FE predictions for lateral-torsional buckling capacities of beams in inelastic portions. A parameter that is dependent on the material properties is introduced in the AS4100 beam buckling strength formula and a new curve for the buckling of HSS flexural members is proposed.

Study of the Torsional Behavior of Aluminum Foam-Filled Galvanized Steel Tubes after High Temperature

Torsional test of aluminum foam-filled galvanized steel tube before and after high temperature is performed. The influence of temperature, porosity of aluminum foam and steel ratio on torsional behavior of aluminum foam galvanized steel tubes were analyzed. Experimental results showed that torsional curves of aluminum foam-filled galvanized steel tube before and after high temperature is similar, and can be divided into four stages: the elastic torsional stage, yield platform stage, descent stage and hardening stage; Its torsional load capacity decreases with increasing porosity of aluminum foam and increases at a higher steel content and slenderness ratio; after high temperature, torsional load capacity of galvanized steel tube decreased significantly. It was found that the strength reduction factor ratio under the elevated test temperature is higher than that recommended by British ECCS, Australian AS4100 and Chinese CECS 200-2006.

Experiments on Distortional Buckling of I-Beams

This paper describes a test program on full-scale fabricated simply supported I-beams with central concentrated load and an effective lateral brace at the midspan of the top compression flange that was performed mainly with the aim of experimental verification and investigation of distortion in doubly symmetric I-section beams. The experimental ultimate loads were compared with the buckling loads of the specimens determined by using the so-called Southwell, Modified, and Massey extrapolation techniques, and in most of the cases very little discrepancy was found between the maximum test and extrapolated loads. Moreover, the experimental beam strengths were compared with the design strengths predicted by the American AISC/LRFD and the Australian AS4100 specifications. Generally, the two specifications provide unconservative predictions in the inelastic range of structural response as the beam length decreases and inelastic behavior becomes more intense. However, the AS4100 specification provides conservative predictions in comparison with the AISC/LRFD specification.

Pertinent issues on the strength design of steel structures to AS4100-1998

This paper describes of an overview to the strength rules in the Australian AS4100 Steel Structures Code that was first issued in Limit States Format in 1990. It focuses on pertinent and characteristic issues, such as the means of analysis for second order effects in frames, and highlights how the tiered approach may lead to efficient design using advanced analysis techniques. It also considers design against buckling in some detail, and shows how advanced solutions may be readily incorporated into the design rules. Implicit in the formulations are the necessity for ductility of the steel, and the scope of the code is limited to steels that display this necessary ductility characteristic.

Inelastic lateral-distortional buckling of continuously restrained rolled I-beams

An energy method of analysis is presented which can be used to study the inelastic lateral-distortional buckling of hot-rolled I-sections continuously restrained at the level of the tension flange. The numerical modelling leads to the incremental and iterative solution of a fourth-order eigenproblem, with very rapid solutions being obtainable, so as to enable a study of the factors that influence the strength of continuously restained I-beams to be made. Although hot-rolled I-sections generally have stocky webs and are not susceptible to reductions in their overall buckling loads as a result of cross-sectional distortion, the effect of elastic restraints, particularly against twist rotation, can lead to buckling modes in which the effect of distortion is quite severe. While the phenomenon has been studied previously for elastic lateral-distortional buckling, it is extended in this paper to include the constitutive relationship characteristics of mild steel, and incorporates both the so-called 'polynomial' and 'simplified' models of residual stresses. The method is validated against inelastic lateral-torsional buckling solutions reported in previous studies, and is applied to illustrate some inelastic buckling problems. It is noted that over a certain range of member slenderness the provisions of the Australian AS4100 steel standard are unconservative.

Inelastic buckling of I-beams with continuous elastic tension flange restraint

Abstract I-section beams may be restrained continuously along one flange. Two common applications of this are in composite tee-beams where buckling may occur in the hogging region, and half-through girder bridges consisting of two parallel I-section beams connected by a deck at the bottom flange level. In these applications, the compression flange is restrained only by the stiffness of the web, and the buckling mode is generally lateral-distortional. The elastic buckling mode in the compression flange is commonly predicted by the U-frame approach, and this method assumes that the half-through girder or composite tee-beam is subjected to uniform bending. The elastic buckling load may then be converted into a design strength utilising the interaction between elastic buckling and yielding. The paper uses an energy method of analysis to study the inelastic buckling of beams continuously and elastically restrained at the tension flange level, being typical of half-through girders. The inelastic buckling strength is predicted by recourse to the U-frame model and to the Australian AS4100 steel structures standard as well as the numerical method, and discrepancies between the design method and the accurate formulation are noted.`

Analysis of buckling tests on beams on seat supports

Eight tests on light full-scale hot-rolled universal beams supported on seats are reported. These tests are analysed by a finite element distortional buckling analysis reported elsewhere. The agreement between test and theory is shown to be good. The code rules given in the Australian AS4100 and in the British BS5950 are compared with the theory and tests, and conclusions are drawn regarding their relative accuracy.

Local buckling of I-sections bent about the minor axis

Abstract The paper presents a modification to an existing semi-analytical complex finite strip method of analysis to incorporate inelastic local buckling based on the deformation theory of plasticity. The method is programmed to investigate the local buckling of doubly-symmetric I-section beams bent about the minor axis. Buckling curves are derived for a variety of geometries. The limiting width to thickness ratios given in the Australian AS4100 for beams bent about the minor axis are shown to agree well with the finite strip predictions.