Barbara Rossi

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.

Combined distortional and overall flexural-torsional buckling of cold-formed stainless steel sections: Design

This paper provides a critical summary of the European standards and design methods available for calculating the strength of cold-formed stainless steel compression members. The standards considered (so far mainly applied to columns failing by flexural buckling) are applied to the case of lipped channel section columns failing by combined distortional and overall flexural-torsional buckling. As observed during the tests presented in a companion paper, distortional buckling is found to have a considerable effect on the cross section resistance and is prone to interact with the global flexural-torsional mode. It is investigated how the different formulations account for the two buckling modes and their interaction and how accurate strength predictions they provide. A new direct strength method taking into account these failure modes is then presented and compared to the test results.

Experimental and Numerical Studies of Ferritic Stainless Steel Tubular Cross Sections under Combined Compression and Bending

AbstractAn experimental and numerical study of ferritic stainless steel tubular cross sections under combined loading is presented in this paper. Two square hollow section (SHS) sizes—SHS 40×40×2 and SHS 50×50×2 made of Grade EN 1.4509 (AISI 441) stainless steel—were considered in the experimental program, which included 2 concentrically loaded stub column tests, 2 four-point bending tests, and 14 eccentrically loaded stub column tests. In parallel with the experimental investigation, a finite-element (FE) study was also conducted. Following validation of the FE models against the test results, parametric analyses were carried out to generate further structural performance data. The experimental and numerical results were analyzed and compared with the design strengths predicted by the current European stainless steel design code EN 1993-1-4 and American stainless steel design specification SEI/ASCE-8. The comparisons revealed that the codified capacity predictions for ferritic stainless steel cross secti...

Robustness of steel and composite buildings suffering the dynamic loss of a column

Abstract In case a vehicle impacts a building frame, one or several columns may be damaged or even completely destroyed. Nowadays, it is a concern to mitigate the risk of progressive collapse of the whole structure further to such a localised exceptional event. Although this robustness requirement is part of several design codes, very few precise practical guidelines are provided, especially as far as dynamic failures are concerned. This paper focuses on building frames suffering the loss of one internal column. The dynamic response is more specifically investigated, with the aim to understand this behaviour in order to eventually derive simplified procedures for robustness assessment. This paper first briefly presents the main previous achievements relate d to the prediction of the static response of a plane frame suffering a column loss. The investigations into the dynamic behaviour are then summarised, which constitute the core topic of the paper. For the sake of simplicity, the dynamic response is described using a basic substructure that was proved to show many similarities in behaviour with a global frame that looses a column. A simplified model is finally developed for the prediction of the considered system’s dynamic response.

Carrying Capacity of Stainless Steel Columns in the Low Slenderness Range

AbstractThe strength of thin-walled stainless steel columns has been investigated extensively over the last few years. In European standards, the concept of section classification for determining the cross section capacity is used. In this system, for Class 4 cross sections, the effective width method (EWM) must be used to account for the effect of local buckling. Because of the complexity and limitations of this method, other methods have been developed, such as the direct strength method (DSM) for cold-formed thin-walled profiles and the continuous strength method (CSM), initially established for members made of nonlinear metallic materials. In the CSM, to take advantage of strain hardening, a deformation-based design approach using a continuous relationship between the cross-sectional slenderness and the cross-sectional deformation capacity is used. To a large extent, the CSM yields accurate predictions, especially in the low slenderness range where the current DSM design procedures for members submitt...

On the evaluation of the through thickness residual stresses distribution of cold formed profiles

The aim of this research is to evaluate the through thickness residual stresses distribution in the walls and in the corners of a cold‐formed open section made of a material presenting a non linear hardening behaviour. To get results as close as possible to the reality, the complete process is modeled, including coiling and uncoiling of the sheet before the cold bending of the corner itself. The elastic springback after flattening as well as after final shaping are also taken into account. In order to validate the model in predicting the residual stresses distribution, the presented results are confronted to experimental measurements and FE results collected from the literature.

Local and interactive post-buckling of RHS thin-walled members - Comparing a new special beam finite element with shell FE models

This paper presents a special thin-walled plane beam finite element that accounts for the in-plane cross-section local deformation. The element is based on the superposition of a classical beam displacement field and of an additional field describing local effects, with an approximation on the local second-order membrane stress field. The theoretical formulation is summarized and an application of the resulting numerical tool to the post-buckling analysis of RHS thin-walled members with moderate local and global slenderness susceptible to both global and local buckling is then performed. Different types of analyses are presented (computation of critical bifurcation loads, geometrically non-linear analysis, geometrically and materially non-linear analysis). The results obtained with the proposed beam finite element are compared to values provided by shell FE models.