Cyclic Testing of a Novel Buckling-Restrained Connection for Mass Timber Structures

Seismic design of tall mass timber structures continues to be challenging because of the limitations associated with the stiffness, strength, ductility, and energy dissipation capacity of traditional timber connections, which are often relied upon as yielding elements. This paper presents experimental testing and a design approach for a novel buckling-restrained connection that combines a glued-in rod with a buckling-restrained axial fuse to form a ductile and fully concealed connection that is potentially replaceable after an earthquake. The connection has high stiffness when compared to traditional screwed or bolted timber connections and overcomes several challenges in their design, including overstrength and a pinched hysteretic response that limits energy dissipation capacity. Cyclic testing of the proposed connection under a range of design configurations is carried out to evaluate its seismic performance in terms of ductility and energy dissipation capacity and a design procedure is proposed. Results of the study demonstrate that the connections can achieve strengths up to 300 kN, with the potential to scale to much higher loads, and achieves the design strength within 10% of the design prediction, resulting in low overstrength. The tested connections consistently achieved ductility ratios above 10 and exhibit wide hysteresis loops without pinching. Repeated testing of a connection after replacing the axial fuses demonstrates the potential for this connection to be a repairable solution after an earthquake.