ABAG Shaken Awake! Report -
Non-Wood-Framed Buildings

4-7 Stories, Built Before 1940

Building Damage Varies by Construction Type

Generally, these buildings consist of cast-in-place concrete buildings built during the 1930s. These apartment buildings typically follow one of two concrete construction systems: either cast-in-place reinforced concrete bearing walls or, cast-in-place concrete frames. These two types of buildings have quite different performance in earthquakes.

Construction and Performance of Buildings with Concrete Frames

Pre-1940 apartment buildings constructed out of a concrete moment-resisting frames are rare. These buildings often include infill masonry walls which usually consist of hollow clay tile or brick.

In pre-1940 buildings, the infill walls are often not reinforced and susceptible to becoming falling hazards in the event of an earthquake. In general, these types of concrete structures, where reinforcing was neither detailed nor installed to give ductile performance, have performed poorly in earthquakes. This type of structure is subject to collapse in the event of an earthquake.

Construction and Performance of Buildings with Concrete Bearing Walls

On the other hand, concrete bearing wall construction can have sound seismic force resisting characteristics. Typically, walls are poured to the level below the floor, then a floor slab is poured, and then the next portion of the wall is poured. The quality of the construction joints between pours become critical. Since the older concrete bearing-wall structures were constructed before the widespread use of plywood, the impression of the horizontal form boards are often left on the exterior walls of the building.

Pre-1940 bearing-wall cast-in-place concrete buildings have performed very well in earthquakes even though they may not have been intentionally designed to resist them. However, in all concrete buildings, non-structural damage to elevators and plumbing may occur.

Buildings in the San Francisco Bay Area

The only county where the number of units of this building type approach 1% of the local housing stock, is San Francisco. Even in this county, they account for only 1.5% of the multi-family housing stock. In the total Bay Area, Type 3 buildings account for barely 0.2% of the total housing stock. It should be reiterated that the combined non-wood building types, Type 3 through Type 6, account for only 2.5% of the total Bay Area housing stock, and that they are mainly present in the older and denser cities of the region.

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.