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RE: Void Forms under Grade Beams

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GM
 
This is a little wierd.  But I bet that the 1500 is the ultimate skin friction (1/2 the cohesion) and the 450 psf is the factored skin friction (SF appx. 3)
 
Are the piers embedded in anything hard?
 
Thanks
 
Arvel
-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com]
Sent: Tuesday, May 24, 2005 2:28 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Void Forms under Grade Beams

Thanks to all. What he is now saying is that I need to design the piers for an uplift skin friction of 1500 psf on the upper four feet of the piers only. This seems way too high to me, since the downward skin friction is only 450 psf….

 

He backed down for the dual requirements, but initially told me I had to design the piers for the uplift on the grade beams even if I used the void forms. Now he wants me to design for a 25 kip uplift from 4 feet of skin friction???? I questioned this too and he’s researching….

 

*head a shakin*

 

-gm

 

-----Original Message-----
From: Arvel L. Williams, P.E. [mailto:awilliams(--nospam--at)gwsquared.com]
Sent:
Tuesday, May 24, 2005 12:18 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Void Forms under Grade Beams

 

Grade beams on void boxes - No Uplift unless tied to floor.

 

Uplift on piers - yes through skin friction, need to account for this in the design and steel in pier.  Geotech should give you active zone (depth) and uplift force per unit area.

 

Note:  If you bell the piers then the tensile stresses are likely to control the steel percentage.

 

Arvel

-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com]
Sent:
Tuesday, May 24, 2005 1:34 PM
To: seaint(--nospam--at)seaint.org
Subject: Void Forms under Grade Beams

I have a soils engineer requiring me to design grade beams for a pier and grade beam residential foundation for an uplift of 1500 psf. He is also requiring void forms underneath the grade beams…. I thought this was an either or type of thing, not both. It’s a 1 story house and this will easily govern the design.

 

Any input appreciated.

 

-gm

SSF, CA