Leroy Gardner is Professor of Structural Engineering at Imperial College London. He is engaged in teaching at both undergraduate and postgraduate level, specialist advisory work and leading an active research group in the area of steel structures. His principal research interests, in respect of which he has co-authored five textbooks and some 300 papers, lie in the areas of structural testing, numerical modelling and the development of design guidance for steel structures. He is a member of the European and BSI Committees responsible for Eurocode 3 and Fellow of both the Institutions of Civil (FICE) and Structural (FIStructE) Engineers. He is Editor-in-Chief of Structures and the International Journal of Steel Structures, and a member of the editorial boards of many other International journals. Prof Gardner was awarded the IABSE Prize in 2017.
Structural steel design by advanced analysis with strain limits
Department of Civil and Environmental Engineering, Faculty of Engineering, Imperial College London
The design of steel structures traditionally involves two key steps – firstly, a structural analysis is performed to determine the internal forces and moments in the structure, and secondly, design checks are carried out on the individual structural members to verify their stability. In design by advanced analysis, both material and geometric nonlinearities are captured during the analysis, hence eliminating the need for subsequent member checks. Only cross-section capacity checks are required. However, the structural analysis of steel frames is typically performed using beam elements. These elements are unable to explicitly capture local buckling, and hence current steel design specifications use the concept of cross-section classification to limit the strength and deformation capacity of a cross-section. This restricts the use of plastic design methods to Class 1 cross-sections, which possess sufficient rotation capacity for plastic hinges to develop. Local buckling prevents the development of plastic hinges for cross-sections with higher classes and, unless computationally demanding shell elements are used, elastic analysis is required. In all cases, the influence of strain hardening is ignored. A more sophisticated approach is set out herein. Firstly, an accurate material stress-strain model for hot-rolled steel, which allows for strain hardening, is described. Secondly, strain limits are employed in the advanced analysis to mimic the effects of local buckling. This allows cross-sections of all classes to be analysed in a consistent advanced analysis framework and to benefit from the appropriate level of force and moment redistribution, depending on the local slenderness of the cross-section. The approach has been applied to individual members, continuous beams and frames and has been shown to bring significant benefits in terms of accuracy and consistency over current steel design specifications.