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Your home and your family might be in danger!!

Highslide JSAn evaluation of structural damage caused by the 2006 Kiholo Bay earthquakes has shown that Hawai'i homes most vulnerable to earthquake damage were post and pier type structures. These homes, where the living area of the home is supported on posts placed on concrete piers, were found to have several areas of structural weakness that can fail during earthquake shaking. We have developed this "Retrofit Expert" system to assist homeowners, who have post and pier type homes, to identify and correct the structural vulnerabilities. The system will provide guidance on how to correct, or retrofit, the vulnerable elements of the home, decreasing the likeliness of damage from earthquakes that occur in Hawai'i.

Studies have shown that the foundation of the structure is the area most likely to fail during an earthquake. A common type of failure is the knee brace. Most diagonal braces are connected to the posts and floor framing with only 2 toenails. During an earthquake, these connections experience tensional (pulling) forces that nails are not designed to resist. For this reason, brace end connections are typically the first elements to fail during an earthquake.

Another area of failure is the connection of the posts to the piers. Most post and pier houses do not provide an anchoring connection between the posts and the foundation piers. Without this connection, frictional resistance is the only bond that prevents the structure from sliding off its supports. Both the vertical and horizontal forces that occur during an earthquake can easily overcome the frictional bond and the structure can "walk" off its foundation piers. The result can rack a house's floor structure.

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To remedy these and other sources of failure, structural engineers recommend the installation of a "continuous load path" that ties the structure to the foundation posts and the foundation posts to the ground. It's only with a continuous, and strong load path that the structure will be able to move with the earth while maintaining structural integrity.

 

What are the options to make my home safer?

Highslide JSOur Retrofit Expert system will ask you a sequence of questions about your home: its shape and size; its location; and the size and lengths of the posts - much like a structural engineer would do if you asked him or her to show you how to make your home stronger and safer. You will need to make a few simple measurements - and we've even designed an on-screen tool that will let you use a photograph to make some of these measurements. The data that you provide to our "expert" will be used to select the appropriate program of retrofits that will enable your home to better survive future earthquakes.

Depending on where you live (in relation to the epicenters of past large earthquakes), our expert may offer as many as three different retrofit designs. If you live in an area where earthquake activity has been infrequent and of lower magnitude, then our Retrofit Option 1 may be adequate for your home. This option consists of installing metal strapping and metal connections to the existing wooden supports and braces. Retrofit Options 2 and 3, which recommend installation of either plywood or masonry shear walls could, alternatively, be installed if you wanted to further strengthen your home's foundation structure, but wouldn't be required to enable your home to survive the likely intensity of shaking forces to which it will be exposed.

Highslide JSIf you live in an area with a higher likelihood of high magnitude earthquakes or intense ground shaking, then Retrofit Option 1 won't be adequate and the Retrofit Expert will recommend Retrofit Option 2 or 3. These options recommend the installation of shear walls of a specialized design as part of the foundation system for your home. Likewise, if your home is a two-story post and pier structure, you will need to install one of the more durable and stronger retrofit options.

 

Retrofit Expert System can help!

To get started with the Retrofit Expert, download and fill out the Retrofit Expert Data Form (see below) with information on your home. If you are uncertain about the information being requested, you can run the Expert System, which includes short animations to help clarify the specific information needed, with approximate or estimated values. After you understand what is being asked, gather the requested information and work through the Retrofit Expert with your measurements. Once you've entered all the required data, the Retrofit Expert will then recommend one or more retrofit designs that are appropriate for your home, along with some detailed drawings and a materials list that you may use to gather the required materials and supplies to complete the job. Of course, if you would prefer to have a contractor take on the retrofit task, these drawings and list of building materials will help you get consistent bids from prospective contractors.

This system is based on the most common home dimensions. An "out of range" means that you should consult a structural engineer.

We have prepared a check list to gather information about your home to get retrofits. You just have to take few measurements and photos of your home to get started!

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