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Re: Flagpole and grade beam design

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Erik,
 
CBC 1805 refers to some very conservative values (1000 PSF minimum) for residential construction. 
 
If by "elasticity" you mean the modulus of subgrade reaction, it can be quite safely estimated per Bowles (e.g., 2nd edition, p. 268, eq. 9-14): ks=36qa (qa - allowable soil pressure in ksf). 
 
For CBC minimum of 1000 psf (an overkill for most of residential construction), ks=36 kcf - compare to 30 kcf for "loose sand" - or 21 pci.  In my experience, this gives you a good basis for the beam on elastic foundation design.
 
Good luck,
 
Steve Gordin SE
Irvine CA
 
----- Original Message -----
From: erik gibbs
Sent: Tuesday, November 07, 2006 9:27 AM
Subject: Flagpole and grade beam design

I am designing a patio cover for a client that wants posts at the entryway, but he does not want to use knee braces to resist the lateral forces. I designed a flagpole embeded in the soil, but the embedment depth is 4.5 ' He said that is too much, can I design a 12"x12" grade beam across the front of the entry way with the stl post embeded into the GB. So to do this I must design the GB for axial load and a moment, but I was told that there needs to be a soils report in order to determine the elasticity of the soil.(by code  CBC). Does anyone know if this is true, I can find anything in the code that talkes about this.
 
Erik Gibbs