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Uplift resistance

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Seth - 
.9D +or- E/1.4 is the correct load combo for seismic overturning.  I believe
that Andrew was referring to wind loads (since he is in hurricane country).
It's not expressed as a "factor of safety" in the UBC, but section 1621.1
stipulates that you can only use 2/3 of the dead load to resist wind
overturning.

I have used Chance helical anchors in northern CA to resist large uplift
point loads.  These may be similar to the devices that others on the list
mentioned.  These are long rods with one or more helical heads on the end
that are screwed into the ground.  The anchors are load tested in place
after installation to insure that they will reach design capacity with a
comfortable factor of safety.  This is a specialized installation, and you
would have to contact the manufacturer to see if there are any qualified
contractors in your area with the experience and equipment to install them.
http://www.abchance.com/

-Karen Casano, SE
San Diego, CA




To: seaint(--nospam--at)seaint.org
From: "Seth W. Cutler" <seth(--nospam--at)rlmorrisonengr.com>
Subject: Re: Uplift resistance

(SNIP)
Overturning force:  I calculated overturning using the load combination 
0.9D - E/1.4.  I did not use an overturning factor of 1.5 because I could 
not find reference for this in UBC 97 for footing or Steel design nor 
general code requirement.  No, this is not design build, but the owner is 
the contractor on this project and every item we add cost to the project we 
get a full discussion about keeping cost down.

I followed the path from 1605.2.2 which directed me to 1611.6 for retaining 
walls and 1626 for seismic.  The retaining wall section requires the 
retaining walls to be designed for 1.5 SF in overturning which does not 
cover what I'm doing.  Section 1626 is the overall section for seismic 
design.  Looking in there, 1630.8 talks about overturning but states simply 
that you need to design it for the story shears.  I also could not find any 
reference under section 18 for footings.  If anyone has any add'l info 
please let me know.

We have also contacted the Geotech on the job and are awaiting a 
response.  I'm just trying to determine what the possibilities are.

Thank you all for your responses and if you have any further insight / 
observations, they are greatly appreciated.

Seth W. Cutler
R. L. Morrison Engineering Co. 


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