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A principal issue in any co-rotational approach for large displacement analysis of plates and shells is associated with the specific choice of the local reference system in relation to the current deformed element configuration. Previous approaches utilised local co-rotational systems which are invariant to nodal ordering, a characteristic that is deemed desirable on several fronts; however, the associated definitions of the local reference system suffered from a range of shortcomings, including undue complexity, dependence on the local element formulation, and possibly an asymmetric tangent stiffness matrix. In this paper, new definitions of the local co-rotational system are proposed for quadrilateral and triangular shell elements, which achieve the invariance characteristic to the nodal ordering in a relatively simple manner and address the aforementioned shortcomings. The proposed definitions utilise only the nodal coordinates in the deformed configuration, where two alternative definitions, namely bisector and zero-macrospin definitions, are presented for each of quadrilateral and triangular finite elements. In each case, the co-rotational transformations linking the local and global element entities are presented, highlighting the simplicity of the proposed approach. Several numerical examples are finally presented to demonstrate the effectiveness and relative accuracy of the alternative definitions proposed for the local corotational system.

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A testing programme was conducted to investigate the material properties of a new highchromium grade of austenitic stainless steel-EN 1.4420 at elevated temperatures. A total of 164 tensile coupons extracted from both cold-rolled and hot-rolled sheets were tested; 80 coupons were tested isothermally with temperatures ranging from 25 °C to 1100 °C, and 84 were tested anisothermally with stress levels ranging from 10% to 90% of the material 0.2% proof stress at room temperature. The experimentally derived reduction factors for the key material properties were compared with existing design values. Design recommendations for the elevated temperature reduction factors were then proposed for this new grade, and a twostage Ramberg-Osgood model was shown to be able to accurately represent the material stressstrain response at elevated temperature.

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The flexural buckling behaviour and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were studied, based on a thorough experimental and numerical modelling programme, and reported in this paper. The experimental programme was performed on three series of specimens, and each series contained five geometrically identical specimens, with one unheated and the other four heated to different levels of elevated temperatures (namely 300 °C, 600 °C, 800 °C and 1000 °C). The detailed heating, soaking and cooling processes, material testing and pin-ended column tests were described, with the derived key experimental results fully presented. The testing programme was supplemented by a numerical modelling programme, including a validation study where finite element models were developed and validated against the test results, and a parametric study where the validated finite element models were employed to derive further numerical results over an extended range of cross-section dimensions and member lengths. Due to the absence of existing design codes for stainless steel structures after exposure to fire, the codified design provisions for stainless steel CHS columns at ambient temperature, as established in the Europe, America 2 and Australia/New Zealand, were assessed for their applicability to stainless steel CHS columns after exposure to fire, based on the obtained test and numerical data. The assessment results generally revealed that the design buckling curve, as adopted in the European code, and the tangent modulus method, as employed in the American specification, lead to unsafe and scattered design flexural buckling strengths for stainless steel CHS columns after exposure to fire, while the explicit approach, as used in the Australian/New Zealand standard, yields a high level of accuracy and consistency in predicting the post-fire flexural buckling strengths of stainless steel CHS columns.