The strain limit state criterion for hollow section joints

Abstract This paper focuses on discussions about establishing the design resistance of hollow section joints, which have now been ongoing for 30 years. The question arose once physical experiments could be replaced by numerical tests and was temporarily solved by agreement on a displacement limit within the IIW. With the advent of design using finite element (FE) solutions and the use of high‐strength steels, this question is being raised once more. Many design guides and standards with considerable international consensus are now available for the design of welded hollow section joints in onshore and offshore construction. However, they typically cover relatively standardized joint types, geometries and loading cases. In the event of unusual joints it is now common for finite element modelling to be performed, but specific guidance needs to be provided on acceptable FE modelling procedures and the interpretation of the output in order to determine a suitable joint design resistance. With this objective in mind, this paper describes appropriate FE modelling and ultimate limit states that can be used; in particular, a 5 % ultimate strain limit state. Application of these ultimate limit states is demonstrated using validated FE models for RHS‐to‐RHS (rectangular hollow section) X‐joints, with braces in axial compression and tension, and brace plate‐to‐CHS (circular hollow section) joints with braces loaded in axial compression.