Compressive resistance of high-strength and normal-strength steel CHS members at elevated temperatures

The compressive behaviour of hot-finished circular hollow section (CHS) steel members in fire is investigated in this paper through numerical modelling. CHS members with high-strength steel grades of S690 and S460 are taken into consideration in addition to those made up of normal-strength grades S355, S275 and S235. Numerical models of CHS structural steel members able to replicate their response in fire are validated. Using the validated finite element models, extensive parametric studies are carried out for the purpose of exploring a broad range of factors influencing the cross-section and member buckling response of CHS steel members under axial compression at elevated temperatures. The accuracy and safety of the design recommendations provided in the European structural steel fire design standard EN 1993-1-2 for the determination of the axial compression resistances of CHS steel members in fire are assessed. New design methods able to provide accurate and safe estimations of the cross-section axial compression resistances and flexural buckling resistances of CHS steel members at elevated temperatures are proposed. The higher accuracy, reliability and safety of the proposed design methods relative to the existing design provisions in EN 1993-1-2 are illustrated

Shear resistance and design of stainless steel plate girders in fire

In this paper, the shear resistance and design of stainless steel plate girders at elevated temperatures are investigated. A broad range of parameters influencing the structural response of stainless steel plate girders in fire are taken into account, considering (i) austenitic and duplex stainless steel grades, (ii) rigid and non-rigid end posts, (iii) different aspect ratios for the unstiffened portions of the plate girders, (iv) various web slendernesses and (v) different elevated temperature levels. The influence of these parameters on the behaviour of stainless steel plate girders at elevated temperatures is considered. Currently, there is an absence of specific design rules on the fire design of stainless steel plate girders in the European structural steel fire design standard EN 1993-1-2. Considering this, an accuracy assessment of the room temperature stainless steel plate girder design recommendations of the European structural stainless steel design standard EN 1993-1-4 applied with the elevated temperature material properties of stainless steel is performed. The results indicate that this approach leads to unsafe and scattered ultimate strength estimations for stainless steel plate girders in fire. New fire design recommendations for stainless steel plate girders that are in accordance with the existing design provisions of EN 1993-1-2 and EN 1993-1-4 are proposed. The accuracy and safety of the proposed new design recommendations are comprehensively verified against the results from nonlinear finite element modelling

Flexural buckling behaviour and design of duplex and ferritic stainless steel I-section columns

In this paper, the flexural buckling behaviour and design of duplex and ferritic stainless steel I-section columns fabricated through the welding of individual hot-rolled stainless steel plates are investigated. Finite element models able to mimic the structural response of stainless steel I-section columns are developed and validated against experimental results from the literature. Employing the validated finite element models, extensive numerical parametric studies are performed for the purpose of comprehensively assessing the behaviour of duplex and ferritic stainless steel I-section columns, considering various member slendernesses and cross-section proportions. The accuracy, safety and applicability of the existing column design provisions provided in the European, North American and Australian & New Zellandian structural stainless steel design standards and guides, some of which are only recommended for the design of cold-formed stainless steel columns, are assessed for the design of welded duplex and ferritic stainless steel I-section columns. Modifications to the column design method given in the current European structural stainless steel design standard EN 1993-1-4 are proposed. The higher accuracy of the modified column design method of EN 1993-1-4 relative to the column design methods in the existing structural stainless steel design standards and guides is illustrated in addition to its safety and high level of reliability

Lateral instability of steel beams in fire : behaviour, numerical modelling and design

The lateral torsional buckling behaviour and design of steel beams in fire are investigated in this paper. Finite element models able to replicate the lateral-torsional buckling (LTB) response of steel beams at elevated temperatures are developed and validated. The validated finite element models are used to carry out extensive parametric studies to explore the LTB behaviour of steel beams in fire, considering various cross-section shapes, member slendernesses, steel grades, elevated temperature levels and different fabrication processes. A design equation for the LTB assessment of steel beams at elevated temperatures is developed on the basis of the results from the extensive parametric studies. The high accuracy, safety and reliability of the proposed design approach are illustrated, which is also compared against the beam design rules existing in the European structural steel fire design standard EN 1993-1-2. The design proposals made in this paper are compatible with the new LTB assessment equations that are due to be incorporated into the next version of the European room temperature structural steel design standard EN 1993-1-1 and lead to more accurate ultimate strength predictions relative to the beam buckling design equations existing in EN 1993-1-2

Stability and design of stainless steel hollow section columns at elevated temperatures

This paper investigates the stability and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures. Nonlinear shell finite element models are employed to conduct comprehensive parametric studies whereby extensive benchmark structural performance data on the behaviour and resistance of stainless steel hollow section columns at elevated temperatures is generated. In total, 26,760 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various member slendernesses, cross-section geometries, cross-section slendernesses and elevated temperature levels. New flexural buckling design rules are put forward for stainless steel hollow section columns in fire, which consistently considers the elevated temperature strength at 2% total strain f2,θ as the reference material strength for all cross-sections classes. The accuracy, safety and reliability of the proposed new design rules are assessed for a wide range of cases. Comparisons are also made against the results obtained through the column fire design rules of the European structural steel fire design standard EN 1993-1-2 [1]. It is demonstrated that the proposed new design rules furnish more accurate, safe-sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the column fire design provisions of EN 1993-1-2 [1]

Simulation and cross-section resistance of stainless steel SHS and RHS at elevated temperatures

This paper investigates the structural response and design of stainless steel square and rectangular hollow sections (SHS and RHS) at elevated temperatures. Finite element models able to replicate the behaviour of stainless steel SHS and RHS members at elevated temperatures are developed and verified against the results from physical experiments, which are then used to perform extensive numerical parametric studies to generate a broad range of benchmark structural performance data on the behaviour of stainless steel SHS and RHS at elevated temperatures. In total, 13860 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel SHS and RHS with a wide range of cross-section properties and subjected to various loading conditions at different elevated temperature levels are considered. A cross-section design method for stainless steel SHS and RHS under different loading conditions at elevated temperatures is proposed, considering the recent design recommendations in [1] for the local buckling assessment of stainless steel plates at elevated temperatures which will be included in the upcoming version of the European structural steel fire design standard EN 1993-1-2. Relative to the current local buckling assessment rules of EN 1993-1-2, the higher accuracy, safety and reliability of the new proposals in the estimations of the ultimate cross-section resistances of stainless steel SHS and RHS at elevated temperatures are demonstrated

GMNIA with beam elements and strain limits based fire design approach for steel beams and beam–columns

The use of advanced analysis techniques harnessing the capabilities of the currently available computational resources can lead to considerably more accurate fire design of steel structures relative to the currently adopted simple fire design methods in practice. In this paper, a structural steel fire design method by Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA) and using strain limits is put forward for the fire design of steel beams and beam–columns. In the proposed fire design method, the GMNIA of a steel member or structure is performed using computationally efficient beam finite elements and strain limits are adopted to account for the detrimental effects of local buckling on the ultimate capacities. To verify the accuracy of the proposed method, extensive numerical parametric studies are conducted through shell finite element modelling. The results indicate that the proposed approach provides accurate and safe ultimate resistance and limit temperature estimations for steel beams and beam–columns in fire, with a considerably higher level of accuracy and reliability relative to the provisions of the European structural steel fire design standard EN 1993-1-2

Fire design of steel columns through second-order inelastic analysis with strain limits

A structural steel fire design approach through second-order inelastic analysis with strain limits is proposed and applied to the fire design of steel columns as a first step in the establishment of a novel fire design framework for steel structures in this paper. The proposed method is carried out using beam finite elements, utilising their computational efficiency. In the proposed design approach, the strength and stiffness deterioration of steel in fire, the spread of plasticity, global instability effects, indirect fire actions and thermal expansion are fully taken into account through second-order inelastic analysis, while strain limits are employed to consider the deleterious influence of local buckling on the ultimate resistance. Ultimate capacity of a steel member or system is determined by (i) the load or temperature level at which the predefined strain limit is attained or (ii) the peak load or critical temperature observed during the analysis, whichever occurs first. A systematic numerical parametric study is carried out through nonlinear shell finite element modelling, taking into account a high number of I-section and hollow section steel columns whose response is considered (i) using isothermal and anisothermal analysis techniques and (ii) with and without axial and rotational end-restraints. It is demonstrated that the proposed fire design approach consistently furnishes significantly more accurate capacity and limit temperature predictions for steel columns in fire relative to EN 1993-1-2 [1] design provisions

Cross-section resistance and design of stainless steel CHS and EHS at elevated temperatures

The structural behaviour and design of stainless steel circular hollow sections (CHS) and elliptical hollow sections (EHS) at elevated temperatures are investigated in this paper. Shell finite element models of stainless steel CHS and EHS are created and validated against experimental results from the literature, which are subsequently used to generate benchmark structural performance data. Parametric studies are performed on a large number of cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS and EHS subjected to (i) pure axial compression, (ii) pure bending, (iii) combined axial compression and bending and (iv) combined bending and shear at elevated temperatures; the studied cases comprise 24,495 stainless steel CHS and EHS in fire and cover a wide range of cross-section slendernesses and elevated temperature levels. Calibrated against the benchmark structural performance data obtained from the numerical parametric studies, new design proposals for predicting the cross-section resistances of stainless steel CHS and EHS in fire are put forward. The accuracy, safety and reliability of the new design proposals are assessed. It is shown that in comparison to the design provisions of the European structural steel fire design standard EN 1993-1-2, the proposed design methods provide more accurate and safe-sided cross-section resistance predictions for stainless steel CHS and EHS at elevated temperatures

Design of web-tapered steel I-section members by second-order inelastic analysis with strain limits

A consistent design approach, performed by second-order inelastic analysis using beam finite elements with strain limits, is proposed for web-tapered steel members. In the proposed design approach, a geometrically and materially nonlinear analysis with imperfections (GMNIA) of the tapered steel member is carried out and the ultimate strength of the member is signified by reaching either the strain limit defined according to the Continuous Strength Method (CSM) or the peak load factor, whichever occurs first. To consider the beneficial effect of strain gradients along the lengths of the members on local cross-section resistances, the strains are averaged over the local buckling half-wavelength. The accuracy of the proposed design approach is verified against results from nonlinear shell finite element modelling as well as a number of experiments on tapered members considering various taper ratios, loading conditions and member slenderness values. The proposed method provides more accurate and consistent ultimate strength predictions than EN 1993-1-1 [1], because the following aspects, which are ignored in traditional design methods, are captured: (1) the interaction between cross-section elements for the consideration of local buckling, (2) the influence of local moment gradients on cross-section resistance, (3) the partial plastification of cross-sections and (4) strain hardening