SECTION 1807 - EMBEDDED POSTS AND POLES 1

[ReverenceEng]

I have been searching for an answer for this for some time, but haven't came across one. Perhaps buried deep in the ENG-TIPS annals...

Anyway, Section 1807 provides the two algorithms for embedded posts and poles depending on a constrained on non-constrained condition.

The variables list 'b' as the "diameter of round post or footing or diagonal dimension of square post or footing, feet (m)."

I am charged with attempting to explain this to a plan checker because our footing, oddly enough, is technically not a square, but super close.

Anyway, I supposed the general question is: if we have a round concrete pier, we get to use the diameter, which is essentially the horizontal the projection of the concrete. But for a square pier, assuming the face of the pier is orthogonal to the load, then the horizontal projection of the concrete is just the width of a face of concrete, whereas we are "allowed" to use the diagonal....so...why? Why the diagonal?

 

[ReverenceEng]

As a follow-on, my assumption is that the use of the diagonal of the square pier will in some way conservatively allow us to account for frictional resistance contribution from the sides of the pier not otherwise engaged in direct lateral bearing without having to use a different, and more complicated, equation. That's 100% my assumption, because I don't know what else it would be.

 

[CarlB]

The attached design guide, on the last page, says use the diagonal because "research shows". Perhaps IBC equation is based on this source, or on the same research.