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Rebar Placement for EV Charger Lightpole

12/11/2021 7:54 PM

We (HOA) will be installing two CT4021 EV Chargers on ChargePoint-specified 2’x2’x2’ “blocks” of concrete. To integrate a pole for lighting, the plan is to imbed ~15” of a 10-foot length of galvanized pipe or rigid conduit at the back of the concrete block. The stackup of dimensions/geometry dictate that the rear edge of the lightpole be located 2” inboard of the back face of the concrete block (see sketch).

I was concerned that any slight flexing of the lightpole where it exits the concrete could cause a failure at the back face of the block. To circumvent this, we decided to add (weld on) a bent length of #3 re-bar near (2” down from) the top face of the concrete block.

Q1. Does this seem like a practical solution to prevent a crack due to pole flex?

Q2. Would an additional wrapping of the top 2” of the imbedded lightpole with foam tape (see enlarged detail in the side view) be of any value in absorbing any flex that might occur?

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#1

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 1:17 AM
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#2
In reply to #1

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 8:03 AM

How much weight is to be mounted at the top of the pole?Will the weight be off center?

Unless you live in tornado alley,I don't think wind is going to be the major load on the pipe.

Rigid conduit and galvanized pipe are not the same thing.Conduit is made to be bent,and is softer,with thinner galvanized coating.

The main stress component would be the bollards.

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#5
In reply to #2

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 11:08 AM

The luminaire weighs 3.75 lbs. it’s cantilevered off of a 12” pipe nipple, coupled to the “mast” via a pipe elbow (see sketch).

Yes, I’m aware of the difference between pipe and conduit, that’s why we’re using pipe (cheaper and possibly stronger). I listed both to tamp down comments about running wires through pipe.

I didn’t mention them, so unsure about the relevance of your bollards comment.

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#4
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Re: Rebar Placement for EV Charger Lightpole

12/12/2021 11:06 AM

Don’t know why aluminum would have any great advantage, but costs are a consideration, hence the galvanized pipe. Same for the “extended pad,” plus a slight slope makes a further extension problematic.

There will be bollards (separately supported and in front) they’re just not shown, and not relevant to my questions.

BTW - You may not recall, but your initial advice on this project lead me to check out ChargePoint and it's been a fairly straightforward project since then - thanks.

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#14
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 9:50 AM

Not knowing your location, you need to consider the clear cover of the rebar as well. If I recall, most jurisdictions call for a minimum of 3" especially in colder climates where deicing salt may be used. And also consider a second "row" of rebar near the bottom of the galvanized pipe.

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#15
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 10:25 AM

ACI indicates 3 inches of cover over reinforcement is required if the concrete is cast against earth. Precast requires less cover for reinforcement protection.

The designer is looking at two issues...protection of the reinforcement metal from ground moisture and a possible tension failure in the concrete if something hits the light pole.

Hence bollards would be recommended (as indicated by Solar Eagle). The suggested reinforcement should help prevent a tension failure. I personally would not place the reinforcement bar against your light pole.

First, the interface of the pole and the concrete is a direct path for moisture to get to the reinforcement. Not right away. But, in time it will. Then, in time, reinforcement will corrode, hence expand, and hence crack your concrete.

Second, Zinc and bare steel are dissimilar metals.

Read the following:

Zinc, which comprises the hot-dip galvanized coating is very high on the Galvanic Series (right), which means it will be anodic to most other metals. So, when hot-dip galvanizing is connected to other metals, the zinc coating will not only sacrifice itself to protect the underlying base steel, but also try to protect the other connected metals. This will lead to a more rapid consumption of the zinc coating, and decrease the overall life.

When it comes to bridge design, the most common other metals that may come in contact with the steel are likely painted (bare) steel, weathering steel, and stainless steel. It would not be recommended to connect bare steel to galvanized steel, as the zinc will want to protect all of the carbon steel and the overall coating performance life will be decreased. However, if the other steel surfaces are painted or isolated with a non-conductive material, these connections will not significantly decrease the life of the galvanized coating as long as the paint or isolating materials are maintained over the coating lifetime.

So, in my opinion, your concrete block needs to be bigger to provide cover over the suggested reinforcement on all sides, not just the side cast against the exterior surface.

Based on that, consider a separate light pole foundation for the light. You may save on the cost.

Good Luck.

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#3

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 9:28 AM

Looks good to me: the foam tape is probably a good idea.

Just a thought: think about adding access to the bottom of the light pole and include a cord when it's installed, so that you can pull an electrical cable through when it's ready for the light.

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#6
In reply to #3

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 11:10 AM

Your comments came closest to addressing my questions. BTW, there will be 1/2” conduit (carrying 14-AWG THHN wires) ported into the bottom of the 1-1/4” pipe, I just didn’t show it for clarity. I have found that the more detail I provide in a post, the more irrelevant or tangential responses I get.

And, if I may ask: Are you answering as a layman, or do you have some Civil Engineering background/training?

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#7
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Re: Rebar Placement for EV Charger Lightpole

12/12/2021 1:03 PM

A conduit elbow,rated for concrete embedding is required at the bottom, with pipe dope on threads and a conduit Ell is required at the top.A plumbing elbow is not to be used for wiring.Rigid Conduit must also be used for wiring.I thought you were going to run the wiring conduit external to the lamp post.Rain tight fittings must also be used.There must also be a minimum of 1/5" of concrete over the conduit in all directions.

I recommend a floor flange for the conduit,instead of embedding.Repair is much easier if it is damaged with a flange.Same recommendation for the light pole.

(And it will be damaged eventually)

Are you licensed and qualified to do this work?

Refer to the NEC for guidance if you are in the USA in most states,but always remember the AHJ has the final word.(Authority Having Jurisdiction.)

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#8
In reply to #7

Re: Rebar Placement for EV Charger Lightpole

12/12/2021 3:57 PM

"And it will be damaged eventually" should be given considerable thought.

Also, I wouldn't plan on welding galvanized unless you really know what you are doing. Well, if you really know what you are doing I don't think you would plan on welding galvanized. I once thought that if I was outdoors and stayed upwind I could ignore the "don't do it" advise and weld galvanized. Holly smoke. No, really, holly smoke. The black smoke was so thick I couldn't see my arc. I also couldn't keep the arc going.

Using a floor flange to allow repairs is a good idea. If you do put galvanized in concrete and want to add something to it I suggest galvanized U-bolts (muffler clamps).

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#11
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 7:36 AM

"I wouldn't plan on welding galvanized" Good Point

https://weldingtroop.com/why-is-welding-galvanized-steel-dangerous/

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#13
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 9:47 AM

You can weld galvanized materials and avoid Metal fume fever" but you must ensure that you do not inhale the weld fumes or wear an appropriate mask. You will need to regalvanize the welded area to slow down corrosion. There are "cold" galvanizing products on the market to do this.

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#19
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 8:04 PM

I tend to suspect that there is a lot more going on than just staying upwind and don't inhale. I couldn't keep an arc due to the thick black smoke. Also, the smoke made the metal very dirty. I agree, somehow it can be done. I also don't think I will ever try again or try to get it done.

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#9
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Re: Rebar Placement for EV Charger Lightpole

12/12/2021 5:26 PM

For attaching the conduit to the post,use this type fittings,one for each size conduit bolted back-to-back,using the rod hanger hole in the center.

As for welding to the post,grind all of the galvanized off of the welding area,then weld it,and apply a cold galvanize spray to it.Several coats.

Most welders refuse to weld galvanized metal because of the toxic smoke produced.

It generates a white smoke(Zinc Oxide) and makes an ugly weld if the zinc coating is left on it.

I also suggest coating the buried part of the post with roofing tar to prevent corrosion.

Forget about the foam tape.When it eventually compresses due to age,UV and weather,you will have a hole around the pipe to catch water and speed up corrosion.

It is also a good idea to drill a small hole at the bottom of the pipe,90 degrees to the load, to drain water that will eventually accumulate inside.I have seen sealed pipes accumulate water over time,and burst when frozen.Trust me,it will gather water inside,somehow.

My theory is that as the temperature changes,it inhales moisture from the air,and it condenses inside the pipe at night.It cannot evaporate all of it during the day,so it accumulates,night after night.

Ask any HAM operator why they drill holes at the bottom of their towers.

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#12
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Re: Rebar Placement for EV Charger Lightpole

12/13/2021 7:45 AM

Total layman.

And in view of several other comments I now withdraw my support for the tape, and, the welding of galvanised steel.

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#10

Re: Rebar Placement for EV Charger Lightpole

12/13/2021 3:52 AM

The design looks good to me. I wouldn't use the flex tape. That would just let water in.

The surrounding soil will fail before the flagpole breaks the concrete.

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#16

Re: Rebar Placement for EV Charger Lightpole

12/13/2021 10:30 AM

It is now clear that you are not a qualified electrician or contractor,and I withdraw all of my suggestions.

Perhaps you are the neighborhood handy man.

Since this is a HOA,surely they can afford to have it done right by a qualified contractor,and avoid potential legal problems later on in the event that something goes wrong.

And I am sure you know Murphy's law.And you know insurance companies' ability to find any way out of paying a claim.

Disregard my previous suggestions.

Do not attempt to use an Ad Hoc design for this project.

Do it right,do it once.

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#17

Re: Rebar Placement for EV Charger Lightpole

12/13/2021 11:02 AM

The rebar would certainly add strength to the pole, but I would much rather see the pole closer to the middle of the block and preferably in the middle. I'm not familiar with the codes for this, but I would think 6" would be the minimum. If you do weld it, grind off the zinc coating first. I would not use the foam tape, as concrete will bond to the metal pipe. However, moisture will penetrate the concrete, so eventually the pipe will rust away. An oil spray will help in that regard.

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#18

Re: Rebar Placement for EV Charger Lightpole

12/13/2021 12:36 PM

Thanks everyone for your feedback. I'm rethinking the whole concept to eliminate the potential problems that have been cited. No need to comment further, as any observations would likely relate to some feature(s) that I have since abandoned.

p.s. To partially address the concerns of some that I am not a qualified electrician, that is true. This was just a concept and I intended to run it by a contractor I've worked with in the past. And licensed contractors will be bidding on this project, so you can rest easy. . .

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