Mass-Timber Structures—Increased Ductility through Friction Mechanism: Fid-Bau Portal

Mass-Timber Structures—Increased Ductility through Friction Mechanism

Sarkisian, M. / Garai, R. / Johnson, B. / Horiuchi, C.

Significant developments have been made for incorporating mass-timber into structures for buildings in regions of low or no expected seismicity. Timber with its limited ductility and traditional connections have limited application of these structures, but a series of connections have been developed to create ductility in otherwise non-ductile systems. This system uses friction to dissipate energy in a major earthquake protecting timber elements and allowing the structure and its components to remain essentially elastic. Mass-timber framed buildings are relatively lightweight compared to structural steel and reinforced concrete buildings. The lower mass of timber buildings result in lower seismic mass. The lightweight benefit is offset by the relatively low seismic ductility of timber systems. These systems typically rely on yielding of steel connectors, yielding of fasteners, and crushing of the wood material for ductility. Enhanced ductility of timber frames will allow designers to realize the full benefit of the lightweight material, improving both the sustainability and resiliency of timber buildings. Three friction energy dissipating devices have been developed: the Pin-Fuse Joint, the Pin-Fuse Frame, and the Link-Fuse Joint. These devices rely on clamping forces from pretensioned high strength bolts to dissipate energy through rotation, or axial displacement, or shear displacement of the joint when the frictional forces are overcome. The devices are used in both moment resisting timber frames and cross-laminated timber shear walls systems. The devices are designed to avoid damage in the timber elements from significant seismic events. This system also allows for centering after an earthquake by releasing bolt pretension and allowing the elastic energy in the timber frame to center the building. The system enhances the ductility of the system and improves the resiliency of the building. This paper will review the theory behind the friction energy dissipaters, application of the devices in timber structures, and compare enhanced seismic design to conventional design mass-timber buildings.