Slide 9 of 10
- One or two story wood frame dwellings with no more than four units are usually simple structures
- Retrofitting them often includes:
- bolts in the sill plate
- plywood on the cripple walls.
- Engineers and building officials have developed guidelines to install these and other items needed for a seismic retrofit. These guidelines are called “prescriptive standards”.
- Prescriptive Standards
- Limited to residential buildings containing one to four units.
- The figure shows a typical simple structure house.
- Large numbers of one-to-four unit wood frame buildings that have structural weaknesses.
- The seismic retrofit for many of these structures are simple to install for contractors and many homeowners.
- Allow building owners to seismically retrofit simpler buildings without having to hire an architect or engineer to prepare drawings.
- Although professional advice is generally desirable and frequently required, prescriptive standards may allow appropriate cost savings. This will make retrofitting more desirable.
- No details are provided in this course; details can be obtained from the City of Los Angeles and/or other major cities.
- Even using the prescriptive method, contractor must still contact the City or County; still obtain permits, approvals etc.
- How do we know that the prescriptive standards work?
- Example: In a neighborhood of bungalow houses, a single 1920s bungalow house had been retrofitted prior to the Northridge Earthquake. After the quake, it was the only house left standing; the only damage was a fallen chimney.
- Remember that houses retrofitted incorrectly can be damaged just as much as those that were not retrofitted at all.