embedded steel pole

[SteelPE]

I have a client who is looking to embed some steel members in the ground to support some solar panels. I have never heard of this and he is convinced that it can be done. Aside from the corrosion issues, how would you calculate the capacity of a steel section embedded into the ground….. would you use the same equations as for sheet piling? Or is this something that would require load testing?

This seems like something he would need to consult a geotech on…. But the project is nowhere near that point yet.

 

[structSU10]

I guess it may be similar to a pile design when it is embeded in the ground. A program like Lpile or something could be used. I'm not sure of the issues that arise with load reversal - I imagine these poles would be taking wind load as cantilevers? I dont know how you deal with the movement back and forth of the column, or how that affects its ability to remain stable.

Most likely i would think a concrete encasement around the steel would be wanted to provide the corrosion protection and so mass for stability and such, but I'm no geotech so I may be missing something.

 

[SteelPE]

The codes being used currently would be AISC and IBC (I'm not sure about IBC as this is not really a building). These embedded poles would be taking wind loads, seismic loads and unbalanced gravity loads. IBC does provide some guidance with embedded poles in section 1807.3 but I'm not entirely sure this section would apply.

 

[azcats]

1807.3 was my initial thought. Why do you think they wouldn't apply?

 

[SteelPE]

azcats

For one thing, it appears as if 1807.3 applies to embedded sections that are square or round. Even if I assume that my WF section is rectangular the section also references table 1806.2 for vertical loads. I wouldn't have much of a cross section to resist vertical loading so I am not sure if the section is still valid.

I suppose I could run some rough numbers using section 1807 to see what type of embedment I would get.

 

[azcats]

Do they intend to drill a shaft, insert member, then backfill with concrete (or something)? Or do they just want to hammer the sections into the ground?

I never considered you were using an WF member. Anytime I'm using this section it's in conjunction with a pipe or tube...and my vertical loads are minimal relative to lateral.

 

[FixedEarth]

On the ones I have worked on, the soils report is ordered first. The soils report should have capacity tables or charts like the ones attached plus corrosion and sulfates. You just pick the embedment depth and then complete your connection design.

Precautions:
1- Manufacturer loadings are based on Stowe position and this is often about 50 mph wind speed.
2- With HP sections, unless the moment is low due to short stanchion, pipe sections work better.
3- If the stanchions are tall, say 10 ft plus, a composite foundation design may work better. You will see the bending moment is too much for driven HP pile, and you may need to encase it in concrete pier in the upper soil zone.
4- If the client insists on concrete less system, the pile foundation Section needed for lateral and moment loads will be much heavier than the stanchion section. So you will need two HP or HSS sections.

 

[PSlem]

Broms' 1965 lateral calcs will give you pipe size. Most supports are helical piles as proper helix selection allows uplift capacity at about same depth as lateral. You need soil report or test piles, wind speed from ASCE7 and racking manufacturer to get mounting and single leg or front and rear leg frames and panel area and angle.

 

[ToadJones]

Unfortunately diving bare steel members for solar projects is the typical installation.
You will need a Geotech.

 

[transmissiontowers]

We embed 12 sided tubular steel poles all the time in the T-Line industry. Typically a hole is drilled in the soil, the pole is lowered, plumbed, and backfilled with some material that is stronger than the old soil. If the soil is poor, a slurry displacement method is used and concrete is pumped in. Sometimes a casing is driven and left in the hole.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[focuseng]

Maybe this?

http://www.macleandixie.com/products/index.asp?DEPARTMENT_ID=2697

haven't spec'd this yet but ran across this on a same situation.

Unfortunately CHEAP pole foundations are the norm for these little "structures". I don't know why they even engage the services of engineers on this because they never listen and argue the whole way about how expensive it is to do what ever is prescribed. I will never do one of these again.

 

[SteelPE]

Thanks for the suggestions. I can tell you that the project is no where near even going forward.... and my client is a steel fabricator with some connections in the solar power industry. It seems like they are trying to reinvent the wheel even before they know if this reinvention is worth the effort.

 

[Splitrings]

ASAE EP 486 Shallow Post Foundation Design is a good reference. It can be download from the ASABE site.