ADVANCED ANALYSIS WITH STRAIN LIMITS FOR THE DESIGN OF STEEL STRUCTURES
Andreas C. Fieber 1*, Leroy Gardner 1 and Lorenzo Macorini 1
1 Department of Civil and Environmental Engineering, Imperial College London, London, UK
Structural analysis of steel frames is typically performed using beam finite elements. These elements cannot capture local buckling explicitly and hence limitations on the local strength and rotation capacity of members are required for design purposes. Traditionally, this is achieved by classifying cross-sections and defining class-specific restrictions on the analysis type (i.e. elastic or plastic design) and cross-section design resistance (i.e. plastic, elastic or effective bending capacity). This approach is however considered to be overly simplistic and creates artificial ‘steps’ in the capacity predictions of structural systems. A more consistent approach is proposed herein, whereby a second order global plastic analysis is performed with strain limits accounting for the effects of local buckling and controlling the deformation capacity of each cross-section. The strain limits are obtained from the Continuous Strength Method. Strains are averaged over a characteristic length to exploit the beneficial effects of moment gradients. The proposed method is applied to members, continuous beams and frames and is shown to be more consistent and user-friendly than current structural steel design methods.
Advanced analysis; Continuous Strength Method (CSM); Local Buckling; Steel Design; Strain Limits