Structural Behaviour and design of stainless steel bolted connections

The increasing importance of sustainability and a transition towards whole life costing has led to an increased interest in the use of stainless steel as a primary structural material. The design of stainless steel structures has traditionally relied upon assumed analogies with carbon steel design thus not accounting for the actual material response which exhibits significant strain hardening and absence of a yield plateau. Thanks to numerous research efforts, several international standards covering the design of stainless steel structures were either recently published or revised recently.

Most published research on structural stainless steel design has focused on the behaviour of individual cross-sections and members, whilst the response of connections remains largely unverified. No significant difference between stainless steel and carbon steel joints is expected regarding the initial rotational stiffness, as the Young’s modulus of both materials is similar and hence the geometric configuration will be determining the rotation stiffness. However, given that connections are subjected to localized high deformation demands in conjunction with the pronounced strain-hardening of stainless steel, carbon steel connection details commonly assumed pinned, may be able to transmit significant moments if they are employed in stainless steel. Moreover, due to the higher material ductility of stainless steel, significant gains in terms of rotation capacity and hence overall ductility and resilience of the structure are expected, however they have not been quantified to date.

This project will assess the applicability of current design provisions of EN1993-1-8 to stainless steel bolted joints. To this end, a series of experiments on bolted stainless steel t-stubs will be conducted to obtain the response of this key joint component in tension and comparisons with the design provisions will be made. Austenitic, ferritic and duplex stainless steel grades will be considered, whilst the geometry of the tested t-stubs will be such that all three failure modes are obtained experimentally. A rigorous FE model will be developed and validated against the experimental results allowing parametric studies to be conducted and design recommendations in line with the observed structural response to be made. Additional numerical analyses on the expected response of stainless steel t-stubs at elevated temperatures will also be conducted, thus allowing a comprehensive set of design rules to be derived for room and elevated temperatures. The outcomes of this project are expected to be adopted in future revisions of design standards.