Overturning moment and directly embedded pole foundations. 1

[HSOLTANI]

I am designing a directly embedded pole foundation for a concrete pole.There is no other data except the pole tip force which has been given by pole manufacturer, and applying this tip force give a very large overturning moment which the typical embedment length of pole is not adequate. In IBC chapter 18, there is just formula for embedment length. I wonder if overturning moment is necessary to be checked in this type of foundations?. Thanks in advance for your assistance.

 

[FoxSE14]

It sounds like the overturning moment is the PRIMARY CONCERN. Not sure what you mean by "typical embedment length." Vary the diameter and embedment to suite. Propose various options of diameter vs. embedment. If the contractor thinks it's too beefy, check your assumptions and re-read the code. If you still get the same results, tell the contractor any deviation is his liability to assume.

 

[atrizzy]

Does the embedment length formula not address the capability of the soil to resist the overturning loads?

 

[TLHS]

Is this a utility pole? The rating makes it sound like it (rated force at tip of pole). Factors of safety are generally smaller, and allowable deflections much higher than in typical structural applications. You'll generally never make typical embedment depths work if you look at them using something like the IBC methodology.

 

[HSOLTANI]

Atrizzy,
Actually my question is that whether IBC equations 18-1 thru 18-3 considers the overturning or not based on lateral pressure of soil and embedment length? IBC doesn't explicitly requires the overturning moment to be checked in anywhere in Chap. 18.

 

[HSOLTANI]

THLS
Yes you are right. It is an electrical distribution concrete pole with total height of 14.5m and tip force of 2500 kg.
As per usual role of thumb method for utility poles the total embedment length will be ( d = 0.1L+0.61m = 2.06m) and the required length as per IBC equations is 2.9m. Since the IBC equations give a larger embedment length, does it consider the overturning effects in Eq. 18-1 thru 18-3?

 

[dik]

Get a copy of SMath Studio and try the attached...

Should have included the depth of the pole for the modified Bowling... 1.8m; it's in the program, but, not in the summary.

Dik

 

[dik]

a *.pdf of the revised...

Dik

 

[HSOLTANI]

Thanks dik,
Very helpful calculation.

 

[JasonMcKee71]

Excellent dik, thanks for sharing!

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
Moment Curvature Analysis
Interaction Diagrams
Reinforcement Design etc.

 

[jec67]

The analysis of a pole such as you describe is often viewed as analogous to a cantilever sheet pile wall. There is a discussion about it in "foundation Analysis and Design" by Bowles. It is in the section covering cantilever sheet pile design.

 

[HSOLTANI]

Thanks jec67