Beam-and-shell element modelling of tubular trusses with welded joints for nonlinear analysis

This study presents a finite element modelling approach for advanced analysis of trusses made of rectangular hollow section members with welded joints. Hybrid beam-and-shell element model is proposed, where truss members are modelled with beam elements and joints with shell elements. The purpose is to incorporate the actual behaviour of joints into the structural model such that it is reflected both in the global response of the truss and locally in a geometrically and materially nonlinear analysis. Ultimately, the goal is to find the load-bearing capacity of the truss by advanced analysis considering the capacity of the joints. This necessitates detailed local joint modelling with proper failure criteria that can be implemented in the analysis. To keep the analysis computationally practicable, simplifications in the joints are done, for example, the welds are not explicitly modelled. The employed shell element model for joints is validated against existing experimental results for selected T- and K-joints. The hybrid beam-and-shell element approach is also applied to a complete truss, and its global behaviour is compared with a full shell element model and a traditional beam element model. To study the capacity of the joints, failure criteria based on deformation and strain proposed in the literature are explored in this study. Moreover, applying the resistance of joints according to EN 1993–1–8 as failure criterion is examined. The numerical studies indicate that, while the global response of the truss is predicted well by the hybrid model, determining suitable failure criteria for the joints requires further research.