Practical strain-hardening material properties for use in deformation-based structural steel design

Abstract

Through the development of an innovative full cross-section tensile testing method, a programme of experiments was conducted to investigate the influence of average cross-section properties on the constitutive relationships for carbon steel, to validate the use of an elastic linear hardening model in practical design, and to assess the resulting accuracy enhancements to the new deformation-based Continuous Strength Method (CSM) of structural steel design. A total of seventeen full cross-section tensile tests on hot-rolled I-sections, hollow sections and cold-formed hollow sections were performed and these were compared with coupon test data obtained from a supplementary programme of fourteen tensile coupon tests and data carefully obtained from the literature. The overall behavioural response of the crosssection tensile tests demonstrated that assuming an elastic, linear hardening material model for the CSM is a reasonable assumption and the previous assumption concerning the magnitude of the strain-hardening modulus, based upon the recommendations of EN 1993-1-5, is overly-conservative. A revised suite of material models was presented and was shown to furnish the CSM capacity equations with a higher degree of accuracy when compared against experimental data.

Stress-strain curves for hot-rolled steels

“…Foster [8] also reported that the yield plateau of full cross-sections in tension was consistently shorter than the corresponding plateau measured in tensile coupon tests, by an average of about 40% and 30% in hot-rolled I-sections and hollow sections, respectively. The ECCS publication [34] recommended a constant strain hardening modulus of Esh = 2%E together with a strain hardening strain εsh of 10εy.…”

“…EN 1993-1-5 [14] permits an elastic, linear hardening model with Esh = 1%E in limit state design using computational methods, and this model has also been employed in the CSM to represent material strain hardening effects [6,7,[15][16][17][18][19]. A series of studies have been conducted to develop suitable expressions for defining Esh in the CSM elastic, linear hardening material model on the basis of tensile coupon test data [29] and full cross-section tensile test results [8].…”

“…6, including the full cross-section tension data from Foster et al [8] and Wang et al [39]. Based on regression analysis, the following equation is proposed to predict εsh for hot-rolled carbon steels:…”

“…Although a number of stress-strain models have been developed for hot-rolled carbon steels [8][9][10], they are either only applicable to a limited strain range or are too complex to be readily implemented in practice. Comprehensive reviews of existing stress-strain models for structural steel have been presented by Huang [9], Foster [11] and Bruneau et al [12], while a brief overview is presented in the following section.…”

Material properties and compressive local buckling response of high strength steel square and rectangular hollow sections

“…The ratio of yield stress f y,cs /f y lies within the range of 0.95 to 1.07, while that for the ultimate tensile strength f u,cs /f u is between 0.96 and 1.16, indicating a relatively small difference between these testing methods for the examined hot-finished high strength steel hollow sections. More significant differences have been found in sections of variable thickness, such as UBs and UCs [44]. The lower fracture strain displayed by the full cross-section tensile tests relates to the gauge length over which it was measured, which was taken as the full length of the specimen, since no standard gauge lengths exist for full cross-sections, hence making the comparisons with the respective coupon test results of limited validity.…”