DIY top of pole rack using superstrut

[totfcboatski]

Anyone have any experience building a top of pole rack system using super strut or unistrut material. I would love to hear some ideas or see some examples or plans.
Thanks!

[peakbagger]

I did a rack with the gold superstrut, I find its a lot easier to work with than the regular dipped unistrut. It worked well but its a small array, roughly 11' wide by 8' high. I used two parallel 3x6 rectangular cross section tubes seperated by one strut width set in concrete. I have three struts, two on the outboard of the rectangular tubes and one in between the tubes with a 3/4" rod drilled through. This allows me to pivot the array seasonally and made it easy to attach the panels in place. By mounting a couple on one side and then pivoting the array and mounting a simiar number ont eh other side, I kept things balanced and could install everthing from a step ladder. It has withstood northern NH winds for 5 winters with no issues. I can change the seasonal tilt in about 5 minutes by myself as its pretty well balanced. My other smaller array on the house which is not balanced, requires a hydraulic jack to move it.

I am considering going up to a 12'6wide x 11' high array. On my original design I used 1/2 height strut for the horizontals with some full height strut behind them for stiffness. I will probably upgrade to full height strut when I go with the larger array. The photo is old, I have added 4 panels (2 on each side) since it was taken.

The biggest hassle is bolting the panels into the strut nuts. No matter what, it requires small fingers to fit either a short bolt in from behind the PV flange and into the strut nut or have a stud sticking out of the strut nut and then having to fit on a washer and then a nut. It sounds easy but much hardware ended up on the ground due to big fingers and a tight space.

Do note, the locality does not inspect electrical and I had to self certify the installation. I am not sure if the NEC code allows non engineered racking so do you homework. I have another array on my house that is made with gold unistrut, it is about 10 years old and has no significant deterioration. There is some external staining where it is up next the cedar siding (which is corrosive). I have looked for but havent seen any galvanic issues between the galvanized strut and the aluminum frames. This is an issue with a coastal installation where there may be salt in the air. Rather than going with aluminum or stainless strut (much more $$), I would have made up some nylon spacers to isolate them. I did install seperate ground clips on each panel frame. If I could come up with an easier clip to replace the panel to strut nut hassle, this design would go up quick, once the concrete is poured. I went through 50 bags of sackrete to pour the base and keeping the columns vertical and centered was a pain to do by myself.

I have a basic cad drawing without a lot of dimensions. I can PDF and send it if you PM me.

[Naptown]

When I built the two pole mounts we basically built a teepee type structure with the peak centered over the foundation hole. hung a chain fall from the center and basically hung the pipe from the top. Got 3 tie down straps and strapped the pipeplumb from the three legs of the teepee. Backed a concrete truck up and poured away. Note the most difficult part was keeping the driver from trying to unload the concrete in 2 minutes which played hell with keeping the first one plumb. When he finally realized he was taking more time as we had to stop and replumb he slowed down on the second and it went much more smoothly.

[totfcboatski]

question

why didnt you just dig and pour your concrete? Im in rural area and have alot of land so it makes sense to just dig and pour.
Question what is the formular for how deep you should go when digging a hole for a top of pole rack and how many yards of concrete? is their an industry driven formula?
thanks
Jeff

[Naptown]

That's what we did. Sonotube was not used we just formed up a little around the top with some flexible material i think it was masonite to neaten up the exposed part.

We used a hole that was 3' in diameter and 6' deep. The size was specified by DPW the rack manufacturer and took into account soil type and wind area. We were also burying 5 feet of pipe in the concrete. We also used fibercon concrete

[russ]

Don't think there will really be a rule of thumb number. Depends on soil type, height and wind load (considering orientation) at a minimum.

The supplier of a rack system would probably have a formula they enter that data in to to come up with a design

[peakbagger]

Formula "P" applies. If in doubt add more pounds. In reality the "rules" are always to go below frost line and make sure the backfill is reasonably course gravel versus clay. If you have the time, what works as well as a solid column of concrete is a flat base slab buried below the frostline with a rebar mat that ties into the rebar inside of a sonotube that runs up to ground level. Once you backfill it properly its just about as good as a big cross section but its more work. My high winds tend to correspond with winter so the ground is generally frozen when the worst winds arise, which stiffens things up.

A PE would have to assume soil bearing capacity to do calcs or would have to do a soils test

[BadgerBoy]

Trying to see the picture of the mount and get started in this forum. Just starting

Ok, trying to see the picture of the mount and also trying to get started in this forum. It looks like you need to do at least one post before they let you see the pictures. So. This is my first post.

I did a rack with the gold superstrut, I find its a lot easier to work with than the regular dipped unistrut. It worked well but its a small array, roughly 11' wide by 8' high. I used two parallel 3x6 rectangular cross section tubes seperated by one strut width set in concrete. I have three struts, two on the outboard of the rectangular tubes and one in between the tubes with a 3/4" rod drilled through. This allows me to pivot the array seasonally and made it easy to attach the panels in place. By mounting a couple on one side and then pivoting the array and mounting a simiar number ont eh other side, I kept things balanced and could install everthing from a step ladder. It has withstood northern NH winds for 5 winters with no issues. I can change the seasonal tilt in about 5 minutes by myself as its pretty well balanced. My other smaller array on the house which is not balanced, requires a hydraulic jack to move it.

I am considering going up to a 12'6wide x 11' high array. On my original design I used 1/2 height strut for the horizontals with some full height strut behind them for stiffness. I will probably upgrade to full height strut when I go with the larger array. The photo is old, I have added 4 panels (2 on each side) since it was taken.

The biggest hassle is bolting the panels into the strut nuts. No matter what, it requires small fingers to fit either a short bolt in from behind the PV flange and into the strut nut or have a stud sticking out of the strut nut and then having to fit on a washer and then a nut. It sounds easy but much hardware ended up on the ground due to big fingers and a tight space.

Do note, the locality does not inspect electrical and I had to self certify the installation. I am not sure if the NEC code allows non engineered racking so do you homework. I have another array on my house that is made with gold unistrut, it is about 10 years old and has no significant deterioration. There is some external staining where it is up next the cedar siding (which is corrosive). I have looked for but havent seen any galvanic issues between the galvanized strut and the aluminum frames. This is an issue with a coastal installation where there may be salt in the air. Rather than going with aluminum or stainless strut (much more $$), I would have made up some nylon spacers to isolate them. I did install seperate ground clips on each panel frame. If I could come up with an easier clip to replace the panel to strut nut hassle, this design would go up quick, once the concrete is poured. I went through 50 bags of sackrete to pour the base and keeping the columns vertical and centered was a pain to do by myself.

I have a basic cad drawing without a lot of dimensions. I can PDF and send it if you PM me.

[inetdog]

If you have the time, what works as well as a solid column of concrete is a flat base slab buried below the frostline with a rebar mat that ties into the rebar inside of a sonotube that runs up to ground level.
A PE would have to assume soil bearing capacity to do calcs or would have to do a soils test

I have seen (on Holmes on Homes) a prefab variation on the sonotube called, I believe, the Bigfoot, which come in two parts, a cylinder and a truncated cone for the bottom which provides a footprint area possibly four times the area of the cylinder. Don't know if you need to use rebar with it or could get away with fibre-added concrete mix. It is primarily designed for downward loads, I believe.
The foot definitely has to be below the frost line.
One big advantage is it is done in just one pour.

One of the recommended uses is Sun Rooms, which is a place to put solar panels, right?

PS: To prevent uplift, they show just vertical rebar running straight down the middle of the tube and the foot. No horizontal runs required.

[russ]

Kind of a strange way to pile something - excavate the area first!

I guess they are not going deep so it isn't a big deal but my civil engineers would fall down laughing.

I would expect them to augur the hole. The instructions for the bottom of the hole "" 2. Base should be placed on undisturbed soil or 4" - 6" of compacted crushed stone or gravel." are kind of cute as well. Well intentioned or CYA they are often difficult to achieve.

[Naptown]

That system may be OK for pier footings for a deck or sunroom but I wouldn't use for a pole mounted solar array.
In order to get the mushroomed portion down in the hole would mean boring an oversize hole. Now you are left with a space around the top tube portion that may be 6 feet or more deep. Since the purpose of the pier is to resist both uplift and more importantly lateral movement trying to compact the ground around that tube would be difficult at best and no where near what undisturbed earth would bear. That and the relative small cross sectional area of the top of the pier doesn't lend itself to resisting lateral movement neatly as well as a large cross section would such as a 3' diameter pier.

[peakbagger]

I have had more than a few designs stamped by Civil PE's (my stamp stays in the drawer unless its mechanical), that used the buried base slab approach. The buried slab (actually a wide footing) I mentioined would be far larger than the "elephants foot" style device that is popular with contractors. Unlike compression loading which is dependent on soil compaction, I think the overturning moment calcs are more dependent on the weight of soil on top of the buried slab. I do agree that a single hole design like a phone pole does depend on undisturbed soil compaction, on the other hand I have seen many poles installed completely in backfill.

In northern NH (and much of the region) we have 2 to 3 foot of topsoil and then glacial till which is basically rocks surrounded by clay. Its hard as a rock when dry but when wet it is pretty marginal stuff. It is rare that any hole can be drilled with an auger type unit due to the rocks, although some folks like the utilities pull it off. The frost line is about 5 to 6 feet down so we have to dig down into the till. About all we can do it make sure not to dig down too deep so we have base for the footing on undisturbed soil and then backfill the hole, so the uplift ends up being more a function of soil weight. Rather than pouring large blocks of concrete from the footing up, it makes sense to install some bent rebar from footing rebar to a slender column with verticals and have that poke up from the ground.

When I did mine I dug down 6 feet and formed up a 2x2 box and encased the steel box sections in the concrete. I really hope I never need to take it out.

[Naptown]

The slab at the bottom adds a tremendous amount of moment to the assembly. In order to move it laterally you need to lift one side of the slab. The fill in this case will act as ballast. Not so much on the rounded thing designed for support as opposed to lateral movement.

[Cipherion]

Economical idea

I did a rack with the gold superstrut, I find its a lot easier to work with than the regular dipped unistrut. It worked well but its a small array, roughly 11' wide by 8' high. I used two parallel 3x6 rectangular cross section tubes seperated by one strut width set in concrete. I have three struts, two on the outboard of the rectangular tubes and one in between the tubes with a 3/4" rod drilled through. This allows me to pivot the array seasonally and made it easy to attach the panels in place. By mounting a couple on one side and then pivoting the array and mounting a simiar number ont eh other side, I kept things balanced and could install everthing from a step ladder. It has withstood northern NH winds for 5 winters with no issues. I can change the seasonal tilt in about 5 minutes by myself as its pretty well balanced. My other smaller array on the house which is not balanced, requires a hydraulic jack to move it.

I am considering going up to a 12'6wide x 11' high array. On my original design I used 1/2 height strut for the horizontals with some full height strut behind them for stiffness. I will probably upgrade to full height strut when I go with the larger array. The photo is old, I have added 4 panels (2 on each side) since it was taken.

The biggest hassle is bolting the panels into the strut nuts. No matter what, it requires small fingers to fit either a short bolt in from behind the PV flange and into the strut nut or have a stud sticking out of the strut nut and then having to fit on a washer and then a nut. It sounds easy but much hardware ended up on the ground due to big fingers and a tight space.

Do note, the locality does not inspect electrical and I had to self certify the installation. I am not sure if the NEC code allows non engineered racking so do you homework. I have another array on my house that is made with gold unistrut, it is about 10 years old and has no significant deterioration. There is some external staining where it is up next the cedar siding (which is corrosive). I have looked for but havent seen any galvanic issues between the galvanized strut and the aluminum frames. This is an issue with a coastal installation where there may be salt in the air. Rather than going with aluminum or stainless strut (much more $$), I would have made up some nylon spacers to isolate them. I did install seperate ground clips on each panel frame. If I could come up with an easier clip to replace the panel to strut nut hassle, this design would go up quick, once the concrete is poured. I went through 50 bags of sackrete to pour the base and keeping the columns vertical and centered was a pain to do by myself.

I have a basic cad drawing without a lot of dimensions. I can PDF and send it if you PM me.

I was informed by the local building department that we would need engineered mounting if we used non-UL listed materials. However using a super strut design would not need engineering. Just thought someone in the design phase may find this helpful and worth a call to their local building regional dept.

[russ]

I was informed by the local building department that we would need engineered mounting if we used non-UL listed materials. However using a super strut design would not need engineering. Just thought someone in the design phase may find this helpful and worth a call to their local building regional dept.

What does the UL listing have to do with a structural member? Nothing so the person you talked to must have misunderstood the question.