Abstract:
The philosophy when designing timber connections is to use many small diameter fasteners in order to ensure that a minimum amount of ductility is present and that the joint will absorb the seismic loads on the structure. However, even if brittle failure of the timber is prevented at the joint, the yielding failure of the timber/fastener combination will include an increased amount of pinching at every subsequent cycle. Designers have accepted this pinching behavior as a characteristic of timber connections resisting cyclic loads. In the paper, a new connector is presented that prevents this pinching behavior in timber connections. The main principle of the connector is based on eliminating the “slack” that occurs at every load cycle. This offers the advantage that the joint fasteners, even in their bent state, can mobilize the full energy-absorbing capacity of the embedment of the timber. In the absence of slack, the governing failure mode becomes Mode-I of the European Yield Model regardless of slender or stocky fasteners used. An experimental demonstration was conducted to show that slender fasteners cross-over from failure Mode-II/III initially to Mode-I eventually, attaining the load plateau as pinching was eliminated with the PFC. With stocky fasteners, the response of the connection on every loading cycle was repeatedly stiff and at a consistent load. In this configuration, a displacement ductility of 10 was achieved. This connection was compared to ordinary brackets in numerical simulations of a rocking shear wall subjected to ground motions. The PFC reduced peak displacements by a factor of 2.8 to 3.2, and post-peak vibrations were substantially muted. This contrasts with the large swings in displacements of the “loose” bracket connection possessing slack. This connector has the potential to alter the design philosophy of using many small doweltype fasteners in timber connections to offer a ductile connection.