A Lego‐like steel‐framed structural system has been developed within the frame of an RFCS project, REDUCE, to facilitate 1) deconstruction of composite structures, 2) circularity at structure and element levels, and 3) serial production in construction by promoting a greater standardization of structural elements. The system utilizes innovative demountable shear connections for composite flooring solutions with precast concrete elements, and adjustable steel connections for use in both beam‐to‐beam and beam‐to‐column connections. The first use case of the structural system has been realized in the Petite Maison project which is a demonstration project for circularity and contributes to the event ESCH2022. Each construction element is linked to a digital database and remains available for future reuse, as a result of the plug‐and‐play, demountable and robust features of the developed system. This paper presents the proposed demountable system, the results from experiments and finite element analyses on the behaviour of shear connections, composite beams, and steel connections, and indicates the analysing methods for structural engineers to open a pathway for full implementation of the structures built into digital tools, fabrication, and construction.

In the last years, new connectors of steel‐concrete composite flooring systems have been developed and investigated to enhance the circularity and standardisation of building components. Recent studies showed that timber can be used as an alternative to the concrete slab in hybrid structures. However, the knowledge in steel‐timber composite flooring systems is still very limited. This contribution presents numerical investigations of steel‐LVL timber composite beams. The load deformation behaviour was determined through 3D finite element models. The design resistance of the composite beams was estimated analytically through a strain‐controlled approach. The results of this study show that the resistances obtained in the numerical models and the strain‐controlled approach are in good agreement. Moreover, obtained deflections and slip values were given at ultimate load.

A series of demountable connections for reusable composite flooring systems and a standardized adjustable steel connection have been developed and tested, to facilitate circular economy as well as the serial production of structural elements and the suitability to be added into BIM or other digital tools. Demountable beam and floor elements and adjustable steel connections form the basis of a Lego-liked 'plug and play' circular framed structural system. This paper presents the proposed circular system, the results from experiments and finite element analyses and indicates the analysing methods for structural engineers to open a path way for fully implementation of the structures 'as built' into digital tools, fabrication and construction.