Pinching-Free Connector for Timber Structures

Abstract

In timber structures resisting earthquakes, slender steel fasteners are traditionally employed to provide ductility in the joints. However, this is associated with pinched hysteresis loops when timber fibers are irreversibly crushed during loading cycles. A pinching-free connector (PFC) was developed to address this issue. In the PFC, crushing-induced slack is effectively absorbed through a ratcheting mechanism. Quasistatic cyclic tests verified that the PFC eliminated pinching. A stocky-fastener configuration of the PFC demonstrated improved reloading stiffness and predictability of resistance under Mode 1 behavior. This enables a smaller overstrength factor of 1.45 compared to 1.6 for conventional connections. Additional ground motion simulations indicate that the PFC reduces peak displacements by 53% relative to conventional connections. As a ratcheting connector, the PFC accumulates crushing deformation on every nonlinear cycle, whether it is small or large in amplitude. Further analyses indicate that the cumulative deformation demand can be estimated at three times the peak connector deformation. With the PFC, few stocky fasteners may be a possible alternative to conventional timber connections requiring many slender fasteners for seismic applications.