Seismic Performance of Confined Sill Plate Connections

In the aftermath of the 1994 Northridge earthquake, extensive field investigations revealed damage in wood frame construction in the form of splitting of the 2 × 4 or 2 × 6 wood sill plates along the line of anchor bolts that typically connect shear walls to the masonry or concrete foundation. Due to the severity of such brittle failures, the city of Los Angeles has recently restricted the use of 2× dimension lumber in sill plates and requires the use of 3× dimension lumber. This paper presents an experimental investigation of the performance of 2× dimension lumber sill plate connections at the yield and ultimate limit states during incremental quasi-static reversed cyclic loading and suggests possible cost-effective retrofit strategies for their improved seismic performance without having to increase the sill plate thickness. Proposed retrofit strategies are based on providing confinement to the sill plate using metal reinforcing straps and reinforcing clamps to increase the deformation capability and energy dissipation capacity of the connection, while maintaining substantial levels of connection strengths.