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Earthquake or Seismic Retrofit

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In areas that are earthquake-prone, a seismic retrofit (the modification of a structure to make it resistant to seismic activity) can provide solutions to the myriad of problems caused by these natural disasters. It is a complex process that your home may need to undergo--either by law or your own judgment for your family safety. Professionals should ultimately be responsible for completing a retrofit project, but the following information will give you an idea of what the project will entail.

Foundation Bolting

Foundation Bolting

Perhaps the largest concern in an earthquake retrofit is ensuring that the frame of the structure does not come loose from the foundation. This is achieved through foundation bolting. The bottom portion of your house's frame is known as the sill or mudsill-- the part that rests on the foundation. Using one of two types of bolts (expansion and epoxy), the sill is secured to the concrete foundation directly or with the aid of attached metal clips.

 


Some foundations are not bolted enough and some aren't bolted at all. Newer homes generally don't require this kind of retrofit, but having a contractor come and check yours is a good idea.

Cripple Wall Bracing

Many homes have a small wall between the bottom of the first floor and the foundation, providing a crawlspace underneath the house. This is known as the "cripple wall". To protect the house from collapsing into the foundation, the cripple wall needs to be reinforced with a brace of structural-grade plywood. The contractors will also check to make sure there is sufficient transfer of earthquake movements between the elements of your home so that no one part receives all of the force for too long.

Cripple walls may also require foundation hold-down brackets under certain problematic walls.

Soft Stories

Living spaces that are located above garages or other open spaces are known as "soft stories" and require retrofitting to prevent them from collapsing into the space below. This can be achieved by engineering a steel frame around the open space to add support--strengthening targeted areas of the home that will provide stability for the room in question, or other, more complex methods of bracing and support.

What You Can Do

While a seismic retrofit requires the assistance of professional contractors, there are some smaller steps you can take to protect your home:

  • Secure water heaters, as well as heavy and tall furniture to prevent them from toppling.

     

  • Make sure all shelves are firmly secured to the wall, and avoid placing very heavy items over your bed or sofa.

     

  • Check for any deep cracks in your walls or ceilings and have tem repaired as soon as possible.

     

  • Check and fasten all of electric cables, faulty fittings and gas leaks because they can potentially become a fire hazard during an earthquake. It is always a good idea to fix flexible pipes for gas and for other purposes to avoid gas leaks.

     

  • To protect glass from breakages, try to install shatter-safe window films.

     

  • Make sure to have an earthquake safety kit in an easily-accessible area of your home.

Earthquake retrofitting is an intuitive and delicate process that, if done incorrectly, could leave your home no more protected than it was before. It takes a good deal of engineering and seismic knowledge to know which bolts to us, which walls need the most support, and what bracing configurations will provide the most stability. Make sure your contractors are well-respected and experienced before choosing any for hire.

Adam Mandelbaum  Posted by Adam Mandelbaum on January 7, 2013

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