Mindful Design Consulting Newsletter (August 2010) How Safe Are Our Buildings in Earthquakes?

So what happens when an earthquake hits our buildings, and how do we (people in the construction industry) design buildings for seismic events? I hope after reading this newsletter you will feel a bit safer inside your home. Well, at least inside the newer homes that are designed using the latest building codes which are constantly updated after large earthquakes hit the US.

There are several factors on how much damage your building can expect in a larger earthquake: proximity to the earthquake fault line, the type of soil your house is built on (available as a geotechnical report for your land before your house was built, the softer the soil, the more damage can be expected), the quality of construction (avoid cheap, inexperienced home builders) and of course the structure itself.

Liquefaction at Niigata

When an earthquake strikes, deep and sandy soils can turn to liquid by a process known as liquefaction, with disastrous consequences for the buildings above.

I will not go into all the details above, but will mention what goes into designing your building’s structure. Structural engineers calculate all the expected loads on your building structure with precision. The sizes of each structural member have to be calculated and spaced at the right distance. Every member connection and every bolt has a designation, particular strength and is used according to a different condition per design. Each building, when in design, is looked at from different perspectives applying different types of loads expected and unexpected (but possible). An earthquake is one of these loads.

Steel Connections

From what I understand, buildings in California in general are designed for 8.0 magnitude earthquakes, which is a rare occasion here. The strongest magnitude earthquake registered in San Diego was below 7. Besides, our structures are typically over-designed, which means even if a magnitude 8.0 earthquake hits your building it should be fine. Only if other factors mentioned above come into play, may your building collapse.

Here is how Michael A. McNeff, S.E., president of McNeff Engineering & Consulting Corp. answered my question on how strong our buildings are designed here in California: “...the building code doesn’t design to certain Richter scale events, but rather postulates the worst expected ground acceleration (earthquake) that would occur approximately once every 2,000 years. It’s impossible to say what exact magnitude this would be, but certainly on par with the great earthquakes of modern times (e.g. San Francisco, Mexico City, Northridge, Iran, etc.). Many of these were over 8.0.”

I hope knowing all this will make you feel a bit safer from now on during our frequent shakes in San Diego.