Risk not so high
- Rebecca Mayer
- Lake Oswego Review - News
School buildings OK, quake study reveals
This fall, the Lake Oswego School District completed an earthquake safety study on seven schools the state rated as high risk in a 2007 report to the Legislature. The results expanded a screening done by the state's Department of Geology and Mineral Industries (DOGAMI) and found none of the buildings to be at risk.
The schools in the study are: Bryant Elementary, Forest Hills Elementary, Lake Grove Elementary, Oak Creek Elementary, River Grove Elementary, Lake Oswego Junior High and Waluga Junior High. (See chart on page A11).
In 2005, Senate Bill 2 required an assessment of education and emergency services buildings in Oregon.
'The DOGAMI is more of a sidewalk survey of these buildings. The work done by (the district's engineering firm) is more in depth,' explained Franz Rad, a professor of civic and environmental engineering for Portland State University.
Rad has done many of those surveys for the city of Portland.
DOGAMI used the federal technique known as FEMA Rapid Visual Screening to identify and rank buildings that are potentially hazardous.
The district's engineer - Froehlich Consulting Engineers - pointed out that an engineer is not required to perform a FEMA screening. The screening is basically a one-page form, they said.
DOGAMI contracted with experienced parties at three major Oregon universities to collect the data.
The screening looked at five key areas: 1) seismic zone (how hard the ground is expected to shake), 2) building structural type (wood frame, reinforced masonry, steel frame, etc.), 3) building irregularities (the shape of the building), 4) original construction date, and 5) soil type (softer soils amplify the severity of ground motion).
The buildings are scored on a scale ranging from 0.0 to 6.8 and relates to the probability that the building will collapse in a 'maximum considered earthquake.' A score of 0.0 suggests a 100 percent chance that a building will collapse, while a 2.0 suggests a 10 percent chance that a building will collapse. DOGAMI categorized the ratings as follows: <0.0 is Very High, 0.1-1.0 is High, 1.1-2.0 is Moderate, and >2.0 is Low.
For example, base scores are given for building structural type as follows: 1.8 for unreinforced masonry construction to 4.4 for light wood-framed buildings that are 5,000 square feet or smaller. Then different elements subtract points to result in a final score.
The district asked Froehlich Consulting Engineers to more fully evaluate the seven high-risk schools identified by the DOGAMI ratings in light of FCE's knowledge of the buildings. Froehlich found that the high-risk ratings from DOGAMI were not warranted.
The FEMA guidebook states that 'buildings identified by this procedure are not necessarily at risk, but should be analyzed in more detail by an experienced structural engineer.'
In most jurisdictions, it is not required that buildings be brought up to code unless there is a large remodel.
'We evaluated (DOGAMI scores) against the actual building plans and our knowledge of each of the schools. We found the scores assigned by DOGAMI to be low. Based on the screening criteria, we found that the buildings should have scored in the range of 2.5 to 3.5, which is in the moderate to low risk range.'
Additionally, six of the seven schools are one-story light framed wood construction, which is at the low end of seismic risk. The seventh school is Oak Creek, which is built with steel framing in 1991 after major seismic updates to the code. Its newer construction should have added more points to its score bringing it a 3.5 rating, they said.
Visit www.oregongeology.com for a complete look at the study.