Monday, October 19, 2015

Earthquake Safety Tips: Identify your building's potential weaknesses and begin to fix them

Buildings are designed to withstand the downward pull of gravity, yet earthquakes shake a building in all directions -- up and down, but most of all, sideways. There are several common issues that can limit a building's ability to withstand this sideways shaking.

This cutaway diagram shows how weak cripple walls can be strengthened by properly attached plywood sheets. [Illustration credit: San Leandro EQ Retrofit Program]

Common building problems

Most houses are not as safe as they could be. The following presents some common structural problems and how to recognize them. Once you determine if your building has one or more of these problems, prioritize how and when to fix them, and get started.

Inadequate foundations. Look under your house at your foundation. If the foundation is damaged or built in the "pier and post" style, consult a contractor or engineer about replacing it with a continuous perimeter foundation. Look for bolts in the mudsills. They should be no more than 1.8 meters (6 feet) apart in a single story and 1.2 meters (4 feet) apart in a multistory building. Adding bolts to unsecured houses is one of the most important steps toward earthquake safety. This can be done by a contractor or by someone skilled at home maintenance. Unbraced cripple walls. Homes with a crawl space should have panels of plywood connecting the studs of the short "cripple" walls (see figure above). You or a contractor can strengthen the cripple walls relatively inexpensively.
Soft first stories. Look for larger openings in the lower floor, such as a garage door or a hillside house built on stilts. Consult a professional to determine if your building is adequately braced.
Unreinforced masonry. All masonry (brick or block walls) should be reinforced. Some communities have a program for retrofitting buildings made of unreinforced masonry. If your house has masonry as a structural element consult a structural engineer to find what can be done. Inadequately braced chimneys are a more common problem. Consult a professional to determine if your chimney is safe.

The best building codes in the world do nothing for buildings built before a code was enacted. While the codes have been updated, the older buildings are still in place. Fixing problems in older buildings -- retrofitting -- is the responsibility of the building's owner.

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