This paper presents the development, implementation, and validation of a macro-element suitable for the linear analysis of innovative 3D plug-and-play joints between tubular columns and lightweight steel truss-girders. The macro-element is based on the component method, accounts for the three-dimensional interaction between the tube faces, and its components have a clear physical meaning. Simplified procedures are developed for the closed-form computation of the stiffness matrix of the macro-element based on the geometric and mechanical properties of the nodal zone. This facilitates practical application in everyday design scenarios. Furthermore, the macro-element's architecture is implemented in the framework of OpenSees as a standalone beam-to-column joint finite element. Validation of the conceptual design is accomplished through parametric studies, comparing its performance with models generated in higher-order finite element commercial software, Abaqus. This research offers a valuable resource for the linear analysis and design of innovative 3D plug-and-play joint connections in structural engineering, enhancing efficiency and reliability in construction practices.

Tubular structures are rather efficient systems due to the ease of fabrication, erection, and the high strength-to-weight ratio of their elements. However, they have seen limited use due to difficulties associated with the design and execution of joints. This scenario has changed over the years as more research focused on the behavior of these structural elements, leading to the appearance of design recommendations for some tubular joint configurations. Recently, a new plug-and-play joint configuration suitable for hybrid modular construction systems, comprising tubular columns, lightweight cold-formed steel truss-girders and cross-laminated timber slabs, has been developed in the scope of the INNO3DJOINTS project (RFCS No. 749959). The mechanical behavior of the structural system was experimentally analyzed, and macro-element models suitable for global structural analysis, explicitly including the joint behavior, were developed. In tubular structures, the out-of-plane behavior of the column’s faces is influenced by the condition of each individual face and the three-dimensional interaction between them. Currently, there is no universally accepted modelling approach for this interaction under various loading conditions. This study addresses this issue and presents a general three-dimensional macro-model for the beam-to-column joints based on the component method and accounting for the interaction between the faces of the tubular column. The architecture of the macro-element of the joint is implemented in a finite element object-oriented software framework, OpenSees, as a standalone joint finite element, and its robustness is verified by using high-order finite element commercial software.