Four things that make buildings likely to suffer significant damage in an earthquake
By David Lee and Alan Klembczyk
If you live in an active seismic region such as California, it is quite possible that you will be seriously affected by an earthquake, sooner or later. Lucky people will suffer damage, often serious, but repairable. Unlucky people will die or be seriously injured. An example of this are the unfortunate residents of Northridge Meadows, which collapsed in the Northridge Earthquake in Los Angeles 23 years ago. Los Angeles is overdue for a large earthquake.
Four things contributing to unsafe structures are outlined here:
- Recent increased estimates of earthquake intensity and newly discovered fault lines.
- Corresponding improvements in building codes means that older structures are not as well-designed as newer ones.
- Non-compliant construction which means that the contractor may have cut corners or made mistakes or both.
- Deterioration over time from earth movement, dry rot, termites, wet rot and water damage.
Recent increased estimates of earthquake intensity and newly discovered fault lines.
There are currently sophisticated instruments to detect the signature of earthquakes all over the country, especially in seismic regions. Engineers have steadily improved their ability to predict the destructive power of earthquakes as well as the type of soil and building structure that will affect performance. Computers can now accurately predict how susceptible a structure is. With each major earthquake, new fault lines and new areas of susceptibility are discovered. The end result is a steadily increasing threat to people and structures.
Strengthening of building codes means that older structures are not as well designed as newer ones.
Many years ago, there were no building codes. Structures were built the same way they had been in the past. Engineers who designed buildings used crude hand analysis. Our understanding has become more exact and shows that previous rules for construction were insufficient. This, combined with the increased estimates of earthquake severity, has already motivated cities to enact ordinances requiring evaluation and/or retrofit of deficient structures.
- Back in 2013, San Francisco created the Mandatory Soft Story Program which was led by the Earthquake Safety Implementation Program and enforced by the Department of Building Inspection to ensure the safety and resilience of San Francisco’s housing. This program targets certain structures including older, wood frame, multi-family buildings with a soft story condition.
- In 2015, the city of Los Angeles passed an earthquake retrofit ordinance that may affect approximately 15,000 buildings that are made from brittle concrete or are wood frame buildings with soft, weak, or open-front walls.
- The City Council of Santa Monica approved their own retrofit requirements earlier this year that may affect 2,000 buildings, some that are steel frame structures.
It is important to note that deficient structures can usually be retrofitted to improve their performance.
Non-compliant construction which means that the contractor may have cut corners or made mistakes or both.
It would be very rare for a building to be constructed strictly according to the approved plans. Sometimes the plans have errors which are discovered late in the construction phase. Sometimes nail spacing is way too sparse. Improper material substitutions could be made. Rebar can be too sparse.
Building inspectors can catch some of these problems, but not all of them. The accuracy of these inspections has increased over the years. The older the structure the more likely that it has major drawing deviations. In fact, the older the structure, the more likely it is that the plans are either missing or incomplete.
Deterioration over time from earth movement, dry rot, termites, wet rot and water damage.
Even if a structure was built to plan, it probably didn’t stay that way. The earth under a building can compress and cause sagging and tilting. This can make the building more susceptible to earthquake damage. Wood structures can be degraded by rot, water damage and termites. Steel structures are susceptible to rust, and may have been weakened by previous earthquakes.
Fortunately, there is technology to protect your home, office or schools. For example, hydraulic dampers, similar to the shocks in your car, can protect buildings and their inhabitants from earthquakes just like the shock absorbers in a car protect you from bumpy roads. They enable a building to efficiently ride out an earthquake and minimize damage.
What You Can Do
Becoming informed and getting involved is always a good idea. Talk to your landlord, your local politicians, or your local building inspectors. They may have more information on what is being done in your area to enhance earthquake performance of your building.
David Lee is the West Coast Technical Liaison for Taylor Devices, Inc., and Alan Klembczyk is Vice President, Sales & Engineering for Taylor Devices, Inc. For more information, visit www.taylordevices.com.