The Direct Design Method (DDM) is a new design method for structural design, in which the entire structure is treated as a system, whose load-carrying capacity is determined by advanced nonlinear analysis without member and connections checks. This means that the structure is designed in one step in conjunction with structural analysis. The DDM allows more economical design of steel structures due to the consideration of material plasticity and redistributions of forces as the system-level.

This research investigates welded joints of structural hollow sections in the framework of the direct design method. This study focuses primarily on welded joints in truss structures, which are often used as main girders in long-span buildings. Members of trusses (top chord, bottom chord and web members) have usually different profiles and typically the web members are connected to chords by welding. Welded joints are typically modelled as hinges so that they do not transfer moments between members. In practice, the interaction of these joints with the truss they are a part of is more complicated. This study aims at more accurate structural modelling of welded hollow section joints such that their behaviour can be incorporated in the DDM. This project aims to develop a reliable and Eurocode compliant method to joint modelling and design by advanced nonlinear analysis.