Method for calculating pole foundation deptt, IBC equation 18-1

[scoteboo]

Hello,
I am using IBC equation 18-1 to calculate the depth of a pole foundation. I'm comfortable with this method, although it does lead to a larger than expected pier foundation (3' diameter, 6.5' depth). Still, it's a small amount of concrete and the bulk of the cost of the construction will be the mob and setup of the drill.... so I'm not too bothered with the size.

My problem is that my design reviewer is giving me lots of push back to reduce the size by incorporate the weight of the concrete footing as a resistance to overturning and as an added resistance to lateral load due to the friction at the base. However my understanding is that the methods described in IBC 1807.3 does not account for either of those things. We've discussed this, but without any success. Perhaps I am missing something, can anyone clarify if I should incorporate the weight of the concrete into my design calcs using this method?

Notes:
- The axial load is minimal (weight of a column) in my design; it is very much a lateral load, creating a moment at the foundation.
- I've allowed for the 1/2" movement by doubling the lateral bearing pressure.

 

[msquared48]

Who is the engineer here? Tell this BO, who is probably in bed with the contractor, where to go.

Mike McCann, PE, SE (WA)

 

[BigH]

Double check against standard highway drawings - you will find a minimum 6' depth and 2.5' minimum diameter/width is typical with larger poles/long arms requiring more depth and footing size.

 

[BUGGAR]

Who is the "design reviewer". There is a big difference between that person being your boss or being the building official.

Bob

 

[woodman88]

If the structure is required to be designed per the IBC, from the 2009 "Section 1807.3 Embedded posts and poles. Designs to resist both axial and lateral loads employing post or poles as columns embedded in earth or concrete footings in earth shall be in accordance with Sections 1807.3.1 through 1807.3.3" or per section 1807.3.2 Design criteria "...or by other methods approved by the building official."

So unless you get approval from the building official I would only use EQ 18-1 for the design.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.