Seismic Fragility Analysis and Retrofit of Conventional Residential Wood-Frame Structures in the Central United States

Abstract

Site-built wood-frame (light-frame) construction is the most common form of construction for residential structures in the United States. Such structures have suffered significant damage in recent earthquakes, and wood-frame construction practices in the western United States (WUS) have improved considerably in the last 2decades. On the other hand, little is understood about the expected performance of wood-frame structures located in the central and eastern United States (CEUS), where the seismicity is moderate compared to the WUS and construction practices seldom provide earthquake resistance. This paper examines the seismic performance of typical one- and two-story wood-frame structures in the CEUS. Six structures with two foundation types were considered, for which conditional limit state probabilities (fragilities) were evaluated considering three possible failure mechanisms: excessive interstory drift, wall uplift, and sill plate splitting. This examination shows that seismic damage to wood-frame structures in the CEUS under earthquakes of moderate intensity is unlikely to lead to loss of life, but may result in significant financial losses. An evaluation of two possible retrofit strategies illustrates how the expected seismic performance of the CEUS structures can be improved by adding more anchor bolts and perimeter sheathing nails to the shear walls.