Structural Engineers

Are you Ready for the Big One?

Contributed by Darrel Harris, Structural Engineer

A major earthquake can strike almost anywhere on the Pacific Rim at any time. It could be today, tomorrow, next week, next year or thirty years from now. Earthquakes are often something that happens to other countries and in different cities from yours but if you are in an earthquake sensitive area, are you ready?

I inspected over 500 buildings after the 1994 Northridge earthquake in Southern California and found that almost all experienced some damage. The total repair job exceeded $4 billion and the lawsuits continue to this day.

Many currently existing buildings do not meet current earthquake standards. The state of­ the art in earthquake engineering has advanced dramatically in the last few years. There are more potential problems in older homes, but some newer homes and other buildings also have hazardous conditions. I urge you to take action now to protect against loss of life and property.

The California Seismic Safety Commission has identified ten potentially hazardous conditions found in many residences. Some may be corrected by the weekend do-it-yourselfer, while others may require professional assistance.

1. Un-braced water heaters may fall during an earthquake, causing fire and water damage. These should be secured by using heavy, metal strapping and lag screws to secure the water heater to the wall studs.

2. The structure may not be anchored to the foundation and slide off the foundation. It is recommended that bolts be drilled through the wall sill plates and into the concrete foundation to secure the building.

3. The house may rest on weak "cripple" walls (between the foundation and the lowest wood floor) which may collapse during an earthquake. Plywood should be added between the wood studs to brace these walls.

4. The house may rest on a pier-and-post foundation, which may collapse. The solution may entail adding a new perimeter foundation and cripple wall braced with plywood.

5. Un-reinforced masonry (usually brick) foundation may break and fail during an earthquake. The best solution is to remove the brick foundation and replace with a reinforced concrete foundation.

6. Un-reinforced masonry walls have been found to be a particular hazard in past earthquakes. Downtown Santa Cruz experienced substantial property damage during the 1989 Loma Prieta earthquake. Correction of this problem may require engaging the services of a Licensed Structural Engineer.

7. Un-reinforced brick chimneys commonly fall when subjected to seismic forces. The best solution is the removal of the brick chimney and replacing with wood.

8. Some newer homes are sited on steep downhill slopes, with a tall wall below the lowest floor. These walls may not be properly braced or anchored to the foundation. It is recommended that the services of a Licensed Structural Engineer be engaged to evaluate the adequacy of houses built on tall walls or posts.

9. Short walls on either side of garage doors (especially if there is a room above) have been found to fail during past earthquakes. You should consult a Licensed Structural Engineer to advise on installing steel bracing or plywood on the garage walls.

10. Other Conditions:

 A. Wood foundations in older homes should be removed and replaced with reinforced concrete foundations.

 B. Old, desiccated concrete foundations should be removed and replaced with new reinforced concrete foundations.

 C. Some newer homes with unusual design or large glass window areas are particularly vulnerable to earthquake damage. A professional Structural Engineer can advise you on how to identify and repair earthquake weaknesses.

In summary, I urge you to take action now. Begin inspecting your residence for potential hazards and strengthen as necessary. The Big One could strike anytime.