Drilled pier subjected to axial and lateral loads

[gmoney731]

Hello,

I have a very basic question. I have a drilled pier/light pole system subjected to a concentric axial load and lateral loads due to the pole, which will cause an associated moment at the base.

My question is, can I just do P/A + M/S, S being the section modulus of the circular caisson, and compare that to the bearing pressure and call it a day?

 

[WARose]

You'd probably get something excessively conservative.....but yes, you can do that.

Be sure your resultant is in the middle third so you get full contact.

 

[JLNJ]

Most light poles have a large moment reaction and a small axial load. This give you a big eccentricity. You can't just do M/S because it gives you tension stresses in the soil (which isn't really possible).

Light poles require some sort of side bearing analysis to make them work.

 

[BridgeSmith]

As JLNJ said, you have to do an analysis for lateral bearing to determine the maximum moment (which will be higher than the applied moment at the base of the pole) to check against the structural capacity, and the deflection. Our pole foundation designs are usually controlled by the deflection limit. We use an automated P-y curve method to analyze many different types of drilled shaft foundations, including those for poles. We use Allpile and Lpile.

 

[Once20036]

For a simplified/one off analysis, IBC provides some equations for this foundation type, I beleive that its in the foundation section of the code.
For more complicated/critical analysis, I believe LPile is a very common program, as mentioned by HotRod