Foundation for a business sign

[johnw2]

I am trying to determine the required foundation design for a business street sign. The sign is 10 feet tall and is 8X10 feet supported by 2 posts into the ground. The soil is typical for middle Georgia. The weight will be minimal. I suspect I would first need to calculate the wind load, then the foundation required to prevent it being blown over. I don't have any experience with this type of design, so PLEASE explain carefully. I am new to this site and any help would be appreciated. John

 

[msquared48]

P/A+- M/S apples here assuming the resultant is inside the kern area of the footing. The footing weight will be the main resisting force againt overturning, and, depending on the local soils, an allowable soil pressure of 1500 psf, or 200 psf with wind, should not be exceeded.

If this footing requires the stamp of an engineer, and if you are unsure of the analysis procedure, you really should enlist the help of a local civil or stuctural engineer to help you.

HINT: If you do not know what the kern area of the footing is, do get the other engineer's help... You can design outside of gthe kern, but that will require diferent equations and incur higher resultant soil pressures.

Mike McCann
MMC Engineering

 

[RWF7437]

There are several other ways to design this foundation.

"WinPost will help you analyze your embedded posts. The program will perform a stress analysis on the posts and determine how deep the posts must be embedded into the ground. The program has a simple section property calculator, soil database and Wind load calculator. You also have the option to enter a single lateral load on the posts as well as an axial bearing load." Archon Engineering about $30.


"........you really should enlist the help of a local civil or structural engineer......".
"

 

[BigH]

Talk to the city or state highway department - they have lots of these signs. They can give you their rules of thumb - and likely a "design brief" of design.

 

[Ron]

johnw2...a few things to consider....

I'm not sure where you are in middle Georgia, but you are potentially in a transition zone between piedmont and coastal plains soils, so there is a fair amount of variability. This will affect your foundation design. The guideline given by Mike is right in the range for these soils without specific geotechnical info.

You indicated it was a "business street sign", implying that perhaps it is in an urban/suburban environment. There is a good potential of buried utilities, so consider that if you are thinking about using shallow drilled piers instead of a "block" of concrete.

Your "foundation" will be a beam that will need reasonably heavy reinforcement due to the moment imposed by a 90-mph basic wind speed for that area, and it will need sufficient mass to resist overturning with a safety factor of at least 1.5. In general, you are probably looking at a 12'x4'x1.5' (LxWxt)concrete section or short drilled piers on the order of d=18" and L=5 or 6 feet. Just ballpark.

 

[abusementpark]

Be sure to use the wind loads on solid signs provisions in ASCE-7-05 to calculate your wind loads.