Semi-rigid behaviour and design of stainless steel bolted connections

Beam-to-column connections are regarded as one of the most critical elements in structures, especially in the case of bare metallic frame construction, as the overall structural performance is highly influenced by the connection behaviour. Significant research on stainless steel members has been reported in the recent past, but research on beam-to-column connections is still scarce. Stainless steel exhibits nonlinear stress-strain response followed by significant strain hardening, which is not appropriately considered in the current design codes, resulting in conservative predictions for member resistances, whilst appropriate design rule for connection design is almost non-existent. The aim of this research is to investigate the semi-rigid behaviour of stainless steel connections and propose suitable analytic models for predicting moment-rotation response of commonly used connection types. Beam-column sections, connecting angles and fasteners produced from the austenitic grade of stainless steel AISI 316L (equivalent to EN 1.4301) were adopted in the current study. Real scale experimental test of three connection types, namely – double web angle (DWA), top-seat angle and top-seat with DWA connections were conducted and are presented in this thesis. A comprehensive investigation on the elasto-plastic deformation patterns was carried out using traditional deformation measuring technique as well as digital image correlation technique; these careful observations allowed to gain in-depth knowledge in assessing overall stiffness, strength and rotational capacity of the considered connection types. 3D finite element (FE) model was developed to replicate the observed experimental behaviour, and good agreement was observed between numerically obtained results and experimental observations. The observed behaviour for the considered stainless steel connections was compared with those obtained analytically for equivalent carbon steel connections; comparisons demonstrated enhanced ductility and significantly higher plastic moment for stainless steel connections. Finally, analytical models were developed based on generated FE parametric results for the connections studied herein. The key connection parameters such as – initial connection stiffness, plastic hardening stiffness and moment capacity can be calculated using the proposed equations by knowing easily obtainable material and geometric properties. Proposed models were shown to produce accurate, reliable and consistent results for full range moment-rotation (M-φ) behaviour of stainless steel connections and, therefore, can be utilised in devising rational design rules for stainless steel connections