JulianConstruction.com: Why Buildings Collapse During an Earthquake

By Shawn Kyles

The 1994 Northridge earthquake lasted approximately 45 seconds. Building damage from the 6.7 quake was extensive and occurred up to 85 miles away. It included the collapse of the Northridge Meadows apartment complex, parking structures at the Northridge Fashion Center and California State University and damage to the area’s freeway system.

Why do buildings and other structures collapse during an earthquake? An earthquake is a sudden release of energy from the earth’s crust that travels in waves. It is caused by a slip in a fracture, also called a fault. The slip or movement can be up, down or horizontal (lateral).

Most buildings are designed to support their own weight (vertical loads). Some attention is paid to lateral loads like the wind, but building design typically focuses on vertical loading.

Depending on the direction of the slip during an earthquake, a building can experience too much lateral or vertical stress, resulting in structural damage or, at its worst, failure. However, it is usually too much lateral load that causes the most damage.

Most houses that have been jolted off of their foundation during an earthquake have to be torn down. The really bad news is that even when a house in uninhabitable following a quake, the mortgage still needs to be paid.

Recently the University of California Irvine and Arizona State University have determined that California is overdue for another major earthquake. Scholars have concluded that major earthquakes in relation to the San Andreas Fault occur every 45-144 years on average. Therefore, our fair region of California is unfortunately far overdue for another colossal earthquake. Experts suggest the next earthquake could range anywhere from 7.0 and up, thus creating chaos and devastation in many heavily populated California cities.

Now, more than ever is the time to prepare for the obvious reality of another impending earthquake occurring in our near future. Older structures can collapse completely, trapping loved ones, and creating lasting injuries and even in the most extreme cases, death.

Retrofitting a home can help prevent earthquake damage. The process involves properly bolting the building’s understructure to its foundation, and bracing cripple walls (short stud walls between the floor and foundation of some houses) with structural-grade plywood. Tying the floor system down with approved framing anchors can also improve your home’s structural integrity.

Depending on the size of the quake, a retrofit may not prevent damage entirely, but it can definitely reduce it. It is also added insurance that you and your family will be kept safe during a seismic event.

The cost for retrofitting a home will vary depending on the size of the home and number of stories.

Older house rarely meet existing safety standards and almost always need retrofitting. In Los Angeles, homes built prior to 1940 were not bolted to the foundation. Some more modern wood frame homes built during the 1970s were bolted down, but came off their foundation during a quake because of improper bracing of the cripple walls.

The best way to determine whether or not your house is at risk for earthquake damage is to request a foundation inspection from an experienced and trained professional. You’ll find out exactly what needs to be done to prevent earthquake damage to your home and protect your family from injury.

Shawn Kyles is an expert in foundation repair & house bolting, and a partner at Julian Construction (http://www.julianconstruction.com) in Los Angeles. He has inspected over 15,000 structures, working with engineering firms & local departments of building & safety. Julian Construction owns its own company and is a “no middlemen” model--no salesmen or subcontractors--you get the principals of the company & its workers under your home. The company’s blog is http://julianconstruction.typepad.com/

Posted via email from Julian Construction's Posterous