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RE: Foundations for Shear Walls

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You need to have some mechanism to resist the uplift forces. If you use concrete dead load, you need to have enough concrete weight to counter the overturning forces. In addition, you can use the weight of soil if you have a mechanism to engage the soil to help resist uplift. But by the time you construct a deeper foundation to save on concrete, you have spent more money on the backhoe and forming. The most commonly used solution is to thicken the concrete under the shear walls to resist the overturning with the dead weight of the concrete.

Another consideration, which can be cost effective, is to use helical anchors and tie them to the concrete footing. It is worth considering. Helicals don't need a lot of specialized equipment to install.

Regards,
Harold Sprague





From: "Mike Rhodebeck" <Mike.Rhodebeck(--nospam--at)bldr.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: Foundations for Shear Walls
Date: Fri, 1 Sep 2006 07:43:41 -0500

We are designing mostly residential structures in high wind country and
are routinely faced with issues of large uplift and download forces - 5
to 20 kips -  generated by overturning resistance forces at the ends of
shear wall segments.  Some conditions have the loads very close
together, as in using a Simpson Strongwall, while others might be 6 to
10 feet apart with conventional wood frame shear wall segments.
Supporting concrete is typically a monolithic slab edge member or
interior thickened slab footer.  How should the concrete be designed?
Is it advisable/required to have enough weight of concrete to resist the
entire uplift?  How are people handling this issue?

Mike Rhodebeck, P.E.
Vice President, Engineering
Builders FirstSource
Florida Design Center, LLC
6550 Roosevelt Blvd.
Jacksonville, FL  32244
904.772.6100  X2285
Fax: 904.317.2835
mike.rhodebeck(--nospam--at)bldr.com

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