Seismic improvement of XLAM-to-foundation connection

Since the late 90s, prefabricated solutions for timber structures widely refer to the use of Xlam panels (also known as CroosLam, CLT or BSP). They can provide load-bearing capacity for both wall and floor elements, ensuring a tri-dimensional distribution of strength and stiffness with low masses, particularly effective in seismic areas. Nevertheless, connections among panels, and between panels and foundation have a crucial role in the overall mechanical performance of the structure. Particularly in case of dynamic actions, e.g., earthquakes, ductile steel devices, e.g., hold-down or angle bracket types, are commonly adopted to connect vertical panels to the foundation and to dissipate energy at the base of the building. Nevertheless, these solutions fail locally in the area nailed to the timber elements, thus providing a limited dissipation capacity and inducing an irreversible damage to the panels. In the paper, an optimized-shape device for the connection of construction elements, able to control the energy dissipation in the seismic zone is proposed. It combines the geometrical and mechanical characteristics of the above mentioned common connectors with the capacity of damper systems, specifically designed to distribute gradually the plasticization in the steel elements. The improved device can be designed to provide strength and stiffness even higher than the most common hold-down connectors, but avoiding the damage of the joined construction elements. Moreover, it can be easily removed and substituted after damage due to the seismic event, if needed. The new device is object of application for Italian Patent n. MI2014A001690 filed on 09/26/2014.