General considerations
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III. Structural Problems and Strengthening
Methods General considerations |
Earthquake upgrading is done for two reasons: first, to guard
against house collapse in an earthquake which could cause deaths
or injuries; second, to reduce damage and economic losses, Major
damage to buildings in earthquakes is usually caused by the
failure of the weakest link in the structural system. Weak links
can be upgraded to match the strength of the rest of the
structural system, but it is not effective to strengthen one
element of a structure to a higher level without strengthening
others. You should also keep in mind that because it is more
difficult to upgrade than to build new, it will probably be too
costly to upgrade an existing building to the strength level of a
new building. However, in most cases, you can significantly
reduce earthquake hazards in your house.
The strengthening measures described in this section are ordered
so that the most important and effective tasks are listed first.
While this priority ranking may not be applicable to all cases,
it is meant to be a guideline for making individual upgrade
plans. The strengthening methods presented here are the most
common ones, although there are other ways to achieve the same
result. Housing design varies greatly in California so the most
appropriate method will depend on each individual house and its
setting. Heavier structures, such as multiple-story houses or
those with tile roofs, may suffer more damage in an earthquake
and should be strengthened accordingly. Strengthening work for
unique buildings, such as those with unusual configurations or
located on steep hillside sites, should be designed by an
engineer or architect licensed in California.
Costs are provided to give a sense of the typical range. The average costs described are associated with construction done in ordinary situations. Strengthening costs will in fact vary from project to project. The costs quoted here are in 1990 dollars and are based on an average one-story Bay Area home approximately 2000 square feet in area on a flat lot. The costs include materials and labor and are what can be expected from a builder. However, if you intend to do the work yourself, you can save a large amount of money because materials account for a only a small portion of the total costs.