Strain Design Limit for Hollow Section Joints

Abstract

This paper focuses on discussions over 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 temporary solved by agreement on a displacement limit within IIW. With the advent of design by finite element (FE) solutions, and the application of high‐strength steels, it is being raised once more. A number of design guides and standards, with considerable international consensus, now exist for the design of welded hollow section joints in onshore and offshore construction. These, however, 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 for a suitable joint design resistance to be determined. Towards this objective, 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 and branch plate‐to‐CHS (circular hollow section) joints, with branches loaded in axial compression.