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Result of the 1994 earthquake in Northridge, California (Photo courtesy of FEMA)
Structural Preparations E-Prep Program: Month #12
There is a 70% chance that you and your family will be at home during the next earthquake. You have a choice as to how well your home will perform. Next to loss of life, the loss of your home will be the greatest catastrophe to occur in an earthquake.
The basic rectangular, single-story, wood frame house is one of the safest types of structures in an earthquake. Most people will be safe at home if they live in a well-braced wood-frame building of one or two stories. These buildings are unlikely to collapse completely during earthquakes. Common damage in these structures is light cracking of interior walls or cracking of brick.
The key to a well-designed building is its ability to withstand an earthquake as a single unit. The shaking and lateral forces of an earthquake will separate building components at their weakest points. Therefore, all structural elements must be securely tied together:
the structure must be tied to the foundation with anchor bolts to keep it from sliding
the wall studs must be sheathed (tied) with plywood or some other material to reduce deflection and provide strength
the floors and roof must be fastened securely to the walls to tie the structure together.
This month's E-Prep activities:
Click on the Structural Preparations link at the bottom of the page to open a folder that contains Preparedness Project sheets for Adding Foundation Bolts, Sheathing Cripple Walls, Strengthening Posts and Beams, and Bracing Outdoor Structures. Print these project sheets out and add them to your Family Disaster Plan notebook for handy reference.
Calendar a morning or afternoon this month to inspect your home and create a "To-Do" list for strengthening the structural components of your home.
If you are uncomfortable performing this inspection yourself, contact an engineer experienced in seismic strengthening. You can find them in the yellow pages of the phone book.
Check your house and garage for foundation bolts. These bolts secure the wood structure to the concrete foundation. They should be a minimum of six feet apart along the sill plate.
For more information on securing your house to the foundation, follow the link at the bottom of the page.
Inspect the vertical studs that extend from the foundation to the first floor of your home. These are common in crawl space areas and are called cripple walls. If they are exposed (for example, without sheathing) on the inside, they could buckle in the ground motion that accompanies many large earthquakes.
For more information on strengthening and bracing cripple walls, follow the link at the bottom of the page.
Inspect all exposed framing in garages, basements, porches and patio covers where beams, posts, walls, floors and ceilings come together. All these components need to be connected with metal connectors.
Check all brick, masonry and stone facades to make sure they are securely attached to your home. Consult a structural engineer for advice on how to do this.
Check the chimney for loose tiles and bricks.
Check the ceiling in the attic surrounding the chimney. It should be reinforced with 3/4 inch plywood nailed to the beams to provide protection from falling bricks that might break through the roof.
If your chimney is old and extends more than five feet above the roof, consider bracing it. Consult a seismic engineer.
For more information specific to masonry chimneys, follow the link below.
Inspect all large plate glass windows to make sure they are safety glass.
Consider adding a safety film to all windows. This does not prevent the window from breaking, but it does keep the glass from falling and injuring loved ones.
If you live in a mobile home, follow the link below for information specific to mobile homes.
