7.2.4: Soft-story Buildings

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Overview

A common failure in California’s recent earthquakes was the two- or three-car garage with living space overhead. Many condominiums have most of the ground floor devoted to parking, with apartments in the upper floors. The large open space at the garage door means less bracing against horizontal forces than in standard walls, so these open areas are the first to fail in an earthquake (Figure 11-6). A wood-frame apartment building is lighter and fares better than a massive concrete structure like a hospital. Similar problems arise on a smaller scale with large picture windows, sliding glass patio doors, or double doors.

Make sure that the wall around the garage door and the wall in the back of the garage, on the opposite side from the door, are sheathed with half-inch plywood, just as cripple walls are. Because of the limitations for bracing on the garage door itself, bracing the back wall, opposite from the door, will increase the overall resistance of the structure to earthquake ground motion sideways to the door.

Plywood sheathing should completely surround any large picture window or set of double doors. The sheathing should be at least as wide as the opening and extend from bottom to top of the opening. The interior wall is finished in drywall or plaster, so the best time to add sheathing is during initial construction or major remodeling.