An investigation into the material response and local buckling behaviour of ferritic stainless steel structural cross-sections is presented in this paper. Particular attention is given to the strain hardening characteristics and ductility since these differ most markedly from the more common austenitic and duplex stainless steel grades. Based on collated stress-strain data on ferritic stainless steel, key aspects of the material model given in Annex C of EN 1993-1-4 [1] were evaluated and found to require adjustment. Proposed modifications are presented herein.The local buckling behaviour of ferritic stainless steel sections in compression and bending was examined numerically, using the finite element (FE) package ABAQUS. The studied section types were cold-formed square hollow sections (SHS), rectangular hollow sections (RHS) and channels, as well as welded I-sections. The models were first validated against experimental data collected from the literature, after which parametric studies were performed to generate data over a wide range of section geometries and slendernesses. The obtained numerical results, together with existing experimental data from the literature were used to assess the applicability of the slenderness limits and effective width formulae set out in EN 1993-1-4 [1] to ferritic stainless steel sections.The comparisons of the generated FE results for ferritic stainless steel with the design provisions of EN 1993-1-4 [1], highlighted, in line with other stainless steel grades, the inherent conservatism associated with the use of the 0.2% proof stress as the limiting design stress. To overcome this, the continuous strength method (CSM) was developed as an alternative design approach to exploit the deformation capacity and strain hardening potential of stocky cross-sections. An extension of the method to ferritic stainless steels, including the specification of a revised strain hardening slope for the CSM material model, is proposed herein. Comparisons with test and FE data showed that the CSM predictions are more accurate and consistent than existing provisions thus leading to significant material savings and hence more efficient structural design.
The usage of stainless steel in construction has been increasing owing to its corrosion resistance, aesthetic appearance and favourable mechanical properties. The most common stainless steel grades used for structural applications are austenitic steels. The main drawback of these grades relies on their nickel content (around 8-10%), resulting in a relatively high initial material cost. Other stainless steel grades with lower nickel content such as the ferritic steels offer the benefits of stainless steels in terms of functional qualities and design but within a limited cost frame. Hence, ferritic stainless steels may be a viable alternative for structural applications. Given the fact that little experimental information on ferritic stainless steels is currently available, the purpose of this investigation is to report a series of material and cross-section tests on ferritic grade EN 1.4003 (similar to 3Cr12) stainless steel square and rectangular hollow sections to enable a better understanding of their material response and structural performance. Four different cross-section geometries have been tested under pure compression and in-plane bending. Measurements of geometric imperfections and material properties are also presented. The obtained test results are used to assess the adequacy of the slenderness limits and effective width formula given in EN 1993-1-4 to ferritic stainless steels, those proposed by Gardner and Theofanous and Zhou et al. design approach.Highlights Experimental study of ferritic stainless steel stub columns and beams Local buckling of cross-sections with different aspect ratios Applicability of various design methods for cross-section design to ferritic stainless steel Design recommendations Keywords Effective width, element interaction, experiments, ferritic stainless steel, slenderness limits, local buckling IntroductionThe chromium present within the internal crystalline structure of stainless steels forms a selfhealing passivation layer of chromium oxide (Cr 2 O 3 ) when exposed to oxygen preventing surface corrosion. Other alloying elements are added to meet specific needs in terms of strength, corrosion resistance and ease of fabrication. Depending on their chemical composition, stainless steels can be classified into main five categories: ferritic, austenitic, martensitic, duplex and precipitation hardening. The most commonly used materials in construction are the austenitic grades which have reasonable mechanical strength with 0.2% proof stress of 210-240 N/mm 2 and display high ductility with ultimate strains ε u laying between 50 and 60%. These positive features, however, may be inhibited by the high initial material cost and considerable price fluctuations associated with the amount of nickel involved in austenitic stainless steels (8-11%). Ferritic stainless steels, on the other hand, contain little nickel leaving chromium as the main alloying element (min. 10.5%); hence, they are price stable and cheaper alloys. In comparison with the austenitic grades, the i...
a b s t r a c tThe web crippling design guides are based on empirical adjustments of available test data. These equations differ from the basic concept underpinning most of the other instabilities, the so-called strength curves. This investigation presents a new design approach for web crippling design of stainless steel hat sections based on strength curves controlled by slenderness-based functions χ(λ). The effects of web crippling on such cross-sections were studied numerically and the obtained results were used to derive the design expressions. Comparisons with tests and FE data, and with design guides show that the proposed design approach provides more accurate web crippling resistance.
Concrete-filled steel tubular (CFST) columns have frequently been utilised in the construction of mid-rise and high-rise buildings as they offer smaller cross-sectional size to load carrying capacity ratio than ordinary reinforced concrete or steel solutions. The steel tube component of CFST columns can be shaped into different forms to further increase its strength and this article focuses on hexagonal CFST short columns in compression. Firstly, the literature is revised and it was found that the available experiments on the hexagonal columns cover relatively limited hexagonal dimensions and material properties. Additionally, existing design models were observed to be inaccurate for certain diameter-to-thickness (D/t) ratios of the columns. Accordingly, this paper intends to widen the available pool of data and proposes a new design model to design hexagonal CFST short columns in compression. This is made herein through comprehensive finite element (FE) models by using Abaqus software, carefully validated against experimental results and subsequent parametric studies covering a wide range of hexagonal dimensions of regular cross-section (circular-like). The effect of various D/t ratios, material steel grades and concrete compressive strengths (fc′) on both the behaviour and strength of the hexagonal CFST short columns is investigated. Based on observations made and conclusions drawn upon analysing numerical data generated, a new design model is presented which provides better strengths compared with available design models and with accurate predictions for the full range of D/t ratios
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