Structural Efficiency of a Hybrid Construction System for a Timber Shell Demonstrator: ReciprocalShell case study

This paper evaluates the structural performance of an innovative hybrid timber system for design and construction of the robotically-fabricated shell structures. The timber system combines two configurations: hexagonal and reciprocal. While the first timber configuration generates the main skeleton of the shell based on the discretization of the input surface, the second configuration enables the cross-bracing within each hexagonal cassette. Joining the cross-bracing elements in the center of the cassettes with a reciprocal node not only resists the deformation of hexagonal cassettes and displacement of elements, but also allows for a more uniform distribution of loads that increases the structural capacity of the timber system, enabling the shell to withstand higher compression and tension forces. The joint system uses the wooden splines and screws to align and reinforce the edge connections, as well as the bolts to fasten the neighboring hexagonal cassettes. The construction system is applied to a case study of a medium-scale shell demonstrator with a maximum span of 7.5 meters that is structurally optimized by form-finding methods. The paper presents a detailed structural analysis including the Finite Element Method (FEM) results, as well as the experimental load test that is carried out to verify the validity and accuracy of the structural calculations.