Pile Embedment - Broms method vs IBC method

Question

Pile Embedment - Broms method vs IBC method

buck1017 (Structural)

(OP)

31 Aug 22 16:00

I have been doing some work with a telecom group and I have been asked to review embedment calcs for a light pole with an antenna on top. Normally for something like this, I use the module built into Tekla TEDDS for "flagpole embedment" which uses the IBC method. The designer who sent me his calc used the Broms method from AASHTO's standard on luminaire design. I checked the design using both methods and similar soil parameters. The required embedment using Broms was 8.5 feet, the IBC method was 20 feet. I have been trying to figure out why there is such a discrepancy. Additionally, the pole is 50 feet tall. A good rule of thumb that I've used in the past is to embed the pole 1/3 the height, which would be about 17 feet. Is the IBC method and therefore the rule of thumb incredibly conservative? Or is the Broms method too simplistic to be accurate?

dik (Structural) · Answer 1 · 2022-08-31 16:35:21

Not having done the sums, but 8.5' for a 50' pole seems a tad light... unless you have really good soil. My SMath calc sheet has 4 or 5 different methods and I select the one that seems to be most appropriate.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

Lomarandil (Structural) · Answer 2 · 2022-09-01 02:35:03

That said, I do consider Brom's method a higher tier analysis than IBC or h/3 rule of thumb method. Especially if your soil data is reasonable.

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just call me Lo.

SlideRuleEra (Structural) · Answer 3 · 2022-09-01 11:18:34

Quote (buck1017)
...embedment calcs for a light pole with an antenna on top.

Electric utility poles are embedded 10% of pole length plus 2 feet... seven feet for a 50' pole. This includes utility poles with (heavy) transformers on top. Depth of 8.5' seems reasonable for a free-standing pole.

MotorCity (Structural) · Answer 4 · 2022-09-01 14:14:36

Double check if either method is assuming restraint at the ground level. It is also common practice to disregard the top few feet from the embedment depth (usually disregard depth equal to foundation diameter).

dik (Structural) · Answer 5 · 2022-09-01 15:04:17

Thanks SRE...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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Pile Embedment - Broms method vs IBC method