ABAG Shaken Awake! Report -
Wood-Frame Multifamily Buildings

4-7 Stories, Built Before 1940

Typical Building Damage

These buildings often lack appropriate shear strength at the base of the structure so that in severe earthquakes they may rack. Also of concern is the connection to the foundation. These buildings often lack appropriate foundation anchorage and the building can move off its foundation under strong shaking. Cracking in the foundation may also occur due to a lack of appropriate reinforcement within it.

Photo of Typical Damage

Source -- Courtesy of the California Office of Emergency Services, Coastal Region

Construction

Most buildings in this category are four-story apartment complexes. As opposed to the post-1940 four-story apartment buildings, most of the pre-1940 four-story buildings are constructed entirely of wood. Typically framed with wood posts, wood joists and stud walls, the exterior walls are usually reinforced with 1x diagonal sheathing boards. A less common form of construction was a first floor of unreinforced masonry, either housing additional units, or a lobby. Finally, this floor may have been built as, or converted to, parking. Such buildings exhibit typical "soft-story" problems, as shown in the photo of the multifamily building damaged in San Francisco during the 1994 Loma Prieta earthquake.

Occurrence of This Building Type in the San Francisco Bay Area

Units in this general type of buildings are a significant part of the housing stock in the older cities in the Bay Area. In the County of San Francisco they account for 6.9% of the total housing stock and 10.5% of the multifamily stock. However, over the entire Bay Area, they comprise only 1% of the housing stock.



ABAG, the Association of Bay Area Governments, is the regional planning and services agency for the nine-county San Francisco Bay Area.

This page is based on a 1996 ABAG report. It was last updated 9/26/03 by jbp.