Kim J.R. Rasmussen

Full-range stress–strain curves for stainless steel alloys

Abstract The paper develops an expression for the stress–strain curves for stainless steel alloys which is valid over the full strain range. The expression is useful for the design and numerical modelling of stainless steel members and elements which reach stresses beyond the 0.2% proof stress in their ultimate limit state. In this stress range, current stress–strain curves based on the Ramberg–Osgood expression become seriously inaccurate principally because they are extrapolations of curve fits to stresses lower than the 0.2% proof stress. The extrapolation becomes particularly inaccurate for alloys with pronounced strain hardening. The paper also develops expressions for determining the ultimate tensile strength ( σ u ) and strain ( ϵ u ) for given values of the Ramberg–Osgood parameters ( E 0 , σ 0.2 , n ). The expressions are compared with a wide range of experimental data and shown to be reasonably accurate for all structural classes of stainless steel alloys. Based on the expressions for σ u and ϵ u , it is possible to construct the entire stress–strain curve from the Ramberg–Osgood parameters ( E 0 , σ 0.2 , n ).

Plate slenderness limits for high strength steel sections

Abstract The paper describes a test programme on stub columns fabricated from BISALLOY 80 steel plates with nominal yield stress of 690 MPa. The programme comprises 18 box, cruciform and I-section specimens. The slenderness of the component plates are chosen in the vicinity of the yield slenderness limit, beyond which the stub column strength is reduced below the squash load as a result of local buckling. The purpose of the tests was to determine whether the yield slenderness limits used in the Australian Steel Structures Standard AS 4100 are applicable to BISALLOY 80 steel plates. The paper also assesses whether the plate strength rules of the Australian Steel Structures Standard AS 4100, the Load and Resistance Factor Design Specification of the American Institute of Steel Construction (AISC-LRFD), the British Standard BS 5950 Part 1 and the European Convention for Structural Steelwork Eurocode3 are applicable to high strength steel. For this purpose, the plate strength curves of these specifications are compared with the BISALLOY 80 test results and with test results from the USA and Japan on high strength steel plates with nominal yield stress of 690 MPa.

Tests of high strength steel columns

Abstract 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.

Network Effects on Scientific Collaborations

Background The analysis of co-authorship network aims at exploring the impact of network structure on the outcome of scientific collaborations and research publications. However, little is known about what network properties are associated with authors who have increased number of joint publications and are being cited highly. Methodology/Principal Findings Measures of social network analysis, for example network centrality and tie strength, have been utilized extensively in current co-authorship literature to explore different behavioural patterns of co-authorship networks. Using three SNA measures (i.e., degree centrality, closeness centrality and betweenness centrality), we explore scientific collaboration networks to understand factors influencing performance (i.e., citation count) and formation (tie strength between authors) of such networks. A citation count is the number of times an article is cited by other articles. We use co-authorship dataset of the research field of ‘steel structure’ for the year 2005 to 2009. To measure the strength of scientific collaboration between two authors, we consider the number of articles co-authored by them. In this study, we examine how citation count of a scientific publication is influenced by different centrality measures of its co-author(s) in a co-authorship network. We further analyze the impact of the network positions of authors on the strength of their scientific collaborations. We use both correlation and regression methods for data analysis leading to statistical validation. We identify that citation count of a research article is positively correlated with the degree centrality and betweenness centrality values of its co-author(s). Also, we reveal that degree centrality and betweenness centrality values of authors in a co-authorship network are positively correlated with the strength of their scientific collaborations. Conclusions/Significance Authors’ network positions in co-authorship networks influence the performance (i.e., citation count) and formation (i.e., tie strength) of scientific collaborations.

Numerical Investigation of the Interaction of Local and Overall Buckling of Stainless Steel I-Columns

This report describes research carried out at the University of Sydney to study the interaction of local and overall buckling in stainless steel I-columns. A finite-element model was constructed using the commercially available ABAQUS software package, taking into account the specific material properties of stainless steel: nonlinear stress-strain behavior, anisotropy, and enhanced corner properties as a result of cold working. The model was verified against the experimental data presented in the companion paper and yielded good predictions of the behavior and ultimate capacity of the test specimens. The finite-element model was subsequently used in parametric studies, which covered the practical ranges of overall and cross-sectional slenderness values. The current Australian/New Zealand, North American, and European design guidelines for stainless steel were assessed using the available experimental and numerical data. It is demonstrated that the current design standards fail to appropriately account for the local overall interaction effect in stainless steel I-columns.

Numerical modelling of stainless steel plates in compression

Abstract The paper describes the development of numerical models for analysing stainless steel plates in compression. Material tests on coupons cut in the longitudinal, transverse and diagonal directions are included as are the results of tests on stainless steel plates. Detailed comparisons are made between the experimental and numerical ultimate loads, load–displacement curves and load–strain curves. It is shown that excellent agreement with tests can be achieved by using the compressive stress–strain curve pertaining to the longitudinal direction. The effect of anisotropy is investigated using elastic–perfectly-plastic material models, where the anisotropic material model is based on Hill’s theory. The models indicate that the effect of anisotropy is small and that it may not be required to account for anisotropy in the modelling of stainless steel plates in compression.

Combined Distortional and Overall Flexural-Torsional Buckling of Cold-Formed Stainless Steel Sections: Experimental Investigations

This paper presents a series of 48 full-scale tests on press-braked stainless steel lipped channel section columns subjected to concentric compression. The tests were carried out between fixed ends in the Structures Laboratory of the University of Liege and the test specimens were designed such that distortional buckling developed in the section prior to overall flexural-torsional buckling. The stainless steel alloy was 1.4003 chromium weldable steel, popularly known as 3Cr12. Three different geometries were tested using the same experimental setup. A critical summary of the standards and methods for calculating the carrying capacity of cold-formed stainless steel compression members is presented in a companion paper by the same writers.

Behaviour of cold-formed singly symmetric columns

Abstract An experimental investigation into the behaviour of cold-formed plain and lipped channel columns compressed between fixed and pinned ends is presented in this paper. It is shown experimentally that local buckling does not induce overall bending of fixed-ended singly symmetric columns, as it does of pin-ended singly symmetric columns. Consequently, local buckling has a fundamentally different effect on the behaviour of pin-ended and fixed-ended singly symmetric columns. In order to show this fundamental different effect caused by local buckling, a series of tests was performed on plain and lipped channels brake-pressed from high strength structural steel sheets. Four different cross-section geometries were tested over a range of lengths which involved pure local buckling, distortional buckling as well as overall flexural buckling and flexural-torsional buckling. The different effects of local buckling on the behaviour of fixed-ended and pin-ended channels are investigated by comparing strengths, load–shortening and load–deflection curves, as well as longitudinal profiles of buckling deformations. The purpose of the paper is to demonstrate experimentally the different effects of local buckling on the behaviour and strengths of fixed-ended and pin-ended channels.

Recent research on stainless steel tubular structures

Abstract The paper summarises research undertaken at the University of Sydney during the 1990s on stainless steel tubular members and connections. The tubes were cold-formed from annealed AISI 304L austenitic stainless steel coil strip. Tests were performed on square, rectangular and circular hollow section columns and beams, as well as welded X- and K-joints in square and circular hollow sections. The paper summarises the design rules proposed on the basis of the tests and describes how these rules are being implemented in the first Australian standard for stainless steel structures currently in preparation.

Bifurcation of locally buckled members

The paper presents a general bifurcation analysis of members that are locally buckled in the fundamental state. The members are assumed to be geometrically perfect in the overall sense such that bifurcation of the locally buckled member in an overall mode may occur. The analysis applies to arbitrary types of loads and support conditions. The cross-section, which may be arbitrary in shape, is assumed to be composed of flat plates. The paper derives the general variational equations expressing equilibrium of the fundamental and bifurcated states. The variational equations are applied to doubly symmetric columns and doubly symmetric beam-columns. The differential equations and boundary conditions are derived from the variational equations and solved for the fundamental and bifurcated states, thus providing the bifurcation loads of the members.