Shape optimization of braced frames for tall timber buildings: Influence of semi-rigid connections on design and optimization process

Abstract With the recent development of timber as a viable structural material for high-rise structures, glulam braced frames have been recently introduced in lateral load-resisting systems of timber buildings. Based on a simple shape optimization problem of a braced frame, this paper explores one of the specificities of timber structures: the influence of semi-rigid connections on their overall structural behavior and design. Dowel-type connections are first studied to obtain a simplified relation between joint stiffness and axial load-carrying capacity. Then, the established local behavior law is introduced in the shape optimization process and design of a discrete braced frame subject to lateral drift constraint under wind load. The problem is solved by a COBYLA optimization method, combined with Optimality Criteria (OC) member sizing techniques. Solutions are then evaluated and compared with classical steel/concrete design. The semi-rigid behavior of connections finally leads to a significant increase in the volume of timber but also affects the optimal shape and topology of the X-braced frame compared with classical results.

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