posted
On page 26 of the Sign Stuctures and foundations book, there is mentioned a "deep base formula" in the first paragraph at the top right of the page. I don't see this formula anywhere in the book. Where am I missing it?
The sign I'm estimating now is 40''x72'', will be 10' up on a pole and so will have a wind pressure of 528lbs(based on 110mph windload).
So based on the WxHxPxC/8000 formula would require .77 yds of concrete. If I used a narrow but deep hole, the earth pressure would be greater but according to this reference, less concrete would be needed. But what formula?
Thanks
-------------------- Wayne Webb Webb Signworks Chipley, FL 850.638.9329 wayne@webbsignworks.com Posts: 7403 | From: Chipley,Florida,United States | Registered: Oct 1999
| IP: Logged |
posted
Hello Wanye, You may want to try to call them, look up under the Bio's.
We like to over estimate when not using an Engineer($300.00-$500.00) to sign-off on a project.
Typically you should always have the diameter of the hole 3 times the diameter of the post/pipe, then apply any additional requirements downward, with a minimum whole depth of 3' clear.
You should also contact your local planning deptartment in person, and request information on simular projects or the advice of the Inspector who is familiar with the local zoning codes.
Good Luck, Ron Percell
-------------------- Ron Percell Percell Signs 707-769-0639 Petaluma, California
posted
Well, I looked all through Peter's book, and I can't find what he's talking about either. What I THINK he is talking about is the same thing you mentioned: A deep, narrow foundation will support more load than a shallow, wide one. As an example, an 8'x 24" foundation will support more load than a 6'x 30" foundation, even though the 6' hole would contain more concrete.
That theory goes out the window however, when you have loose sandy soil. In that case the foundation does not rely on the support of the surrounding soil, but more on the sheer weight of the concrete.
As far as Peter Horsley's "quick formulas", he states that these should only be used for estimating purposes. In other words: when I'm preparing a bid, about how big of a hole am I going to have to dig, and about how much concrete am I going to have to buy. When it comes to the actual structural drawings, and the installation, you are going to have to do the full engineering formula.
Here's a formula that's a little simpler than Peter's. It's by Merv McIntyre and was published in Sign Builder Illustrated in the November-December 1992 issue.
-------------------- Jerry Mathel Retired Grants Pass, Oregon signs@grantspass.com Posts: 916 | From: Grants Pass, OR USA | Registered: Dec 1998
| IP: Logged |
Printer-friendly view of this topic