I'm mounting unisstrut on the roof and want to screw into the strongest place. It seems the areas between the rows of rivets lie above structural cross-members. If so that seems to be the area to mount the unistrut.
One length seems overlapped, can one assume there are two sheets of roofing there?
Any suggestion on types of screws to fasten the struts? Is the cross beam solid or has holes so a screw may not get into the cross-beam?
I can't comment on MCI construction but will make an informed recommendation to stay with stainless steel fasteners. SS self tapping screws will self tap fine in aluminum but if any part of the structure being fastened to is steel or ferrous - the SS self tappers will not do well. In that case I would recommend drilling, tapping, then using SS machine screws. Further more I used mechanical sealing SS neoprene bonded washers and stayed away from any kind of caulking. 2ndary means of sealing (below the SS neoprene bonded washer) could be a superior gasket making product called "The Right Stuff" used on the threads but would bet moisture won't get that far... My 2 cents & time-road tested...
Might try riv-nuts, where you drill a hole incert the riv-nut and use the riv-nut gun to fasten and it anchors it behind whatever panel you put it in. Much like an expansion anchor then just bolt it down to that. :^
Good ideas. The existing rivets only guide you through solid sheating but not necessarily into the solid cross member. . I like Dave's idea but unless you know there is sufficient backing material then it may not grip into the cross-member.
SS machine screws are the call for sure. I'm still considering using 3M 5200 to secure the unistrut to the exterior roofing in addition to the screws. Grinding both surfaces this time should ensure full bonding and waterproofing around holes as well.
Any suggestions on machine screw size, spacing, and pattern? This is a forever-mounted set of brackets. LOL
Don said
"Any suggestions on machine screw size, spacing, and pattern? This is a forever-mounted set of brackets. LOL"
IMO 1/4" hardware is stronger than required.
Riv-nuts are great for sheet metal as in body panels but shooting for structural frame under the body panel tapping should yield enough thread thickness.
If you have a manual, the whole structure is shown along with body panels.
Merle ;)
Don I wouldn't lay it on the roof. It should be up on at least 1/4" standoffs so water can pass under it. :^
You are going to use aluminum Unistrut?
In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.
Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.
Quote from: hogi6123 on July 07, 2021, 08:39:05 AM
In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.
Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.
With steel in the works I'd shy away from penetrating a lapped joint (as you may create issues unrelated to trying to firmly hold the panels - dissimilar metals) and shoot for just body roof panel with what Dave mentioned: riv-nuts making certain they are all aluminum with SS hardware.
With all due respect, I was cringing to your original diy of adhesive only attachment to the roof. We have successfully used oversized (to what the solar panel mfger supplied in ferrous) SS self tapping screws into the roof panels only. These buses are robust when it comes to roof panel aluminum guage. Got some freeway milage on the panels and they are doing fine. If we see any reason for concern we will change out the self tappers for aluminum riv-nuts but currently confident of the install. Fwiw.
Thanks for the ideas and the diagram of the panels secured to the cross-member.
I see two options then. 1) Riv-nuts penetrating the double sheeting. 2) remove original rivet that is through both sheets and the cross-member. Replace with SS machine screw or Riv-nut.
The uni-strut I'm looking at is steel and if placed on standoffs, then no adhesive bonding would be used. All the strength comes via the Riv-nut or machine screws.
I'm still convinced that if I had ground the surface coating off the galvanized brackets it would have held up. But this setup ain't going anywhere. lol
I'm planning on running the unistrut the full length if ever anything needed to be secured up top the railing is all there.
Where will you attach the TAILS? :^ :)
how about Huck rivets? they really hold, but you need long handled tool to set them.
Quote from: hogi6123 on July 07, 2021, 08:39:05 AM
In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.
Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.
Eagles have that same support structure
If you decide to use Rivnuts,, then be sure to measure thru the drilled holes to determine the TOTAL THICKNES OF ALL PANELS.. A rivnut has to have the correct "gip length" to hold properly..>>>Dan
Quote from: Utahclaimjumper on July 07, 2021, 06:07:13 PM
If you decide to use Rivnuts,, then be sure to measure thru the drilled holes to determine the TOTAL THICKNES OF ALL PANELS.. A rivnut has to have the correct "gip length" to hold properly..>>>Dan
Just like a rivet...
Just like a pulled rivet.>>>Dan
OK, looks like the rivet nut is the winner. I like how you have a threaded hole to bolt stuff into the rivnut and very easy to remove.
At quick glance, it seems there are different products sold as rivnut. Which brand do you recommend? Also, which style rivet installer, looks like different styles.
thanks
Can't speak to the different brands, but I can speak to one point - when you use the install tool you've got to practice to get the required pressure down. Too much pressure on the install tool and the threads distort. Too little and the rivnut wiggles in the hole or pulls out.
Explore different ways to seal the rivnut as well, as the ones I've found don't have any built-in seals to make them water tight. Usually I use a neoprene washer against the rivnut, then a thin flat washer, and then whatever I'm trying to mount.
The best mechanical means to weather proof a riv-nut fastener penetration is with slight conical neoprene bonded SS washers. There are also SS neoprene "well nuts" that work similar to a riv-nut but are a neoprene barrel instead of a metal barrel which expands underneath the surface & have tremendous holding power & a tight seal. Our whole bus barn which is constructed of corrugated FRP siding on structural metal framing has thousands of these well nuts including on the almost flat roof line. It was a fastener of the trade in industrial cooling tower construction where forced water flow was kept inside of the structure. They are the ultimate & free in my case...
Any thoughts on spacing and placement of the rivnuts along the unistrut. Some say not to mount the railing flush to the surface to allow water to flow under the railing. What I'm thinking is to use a piece of aluminum plate maybe 4" long, 1/8" thick, put a hole so rivnut can go through. That would provide a strong stable platform for the unitstrut to lay against.
Are you framing the 14x14 cut out with Unistrut ? the big guys with 5 or 6 roof tops use no rivet's or nuts only strips of metal with the 3m 5200.There are 2 strips of 1/8 metal with a 14 inch spacing bonded to the roof from front to rear between the roof bows.ac units with the 90 to 100 lb weight spread out has very little per square inch weight
Nope he is installing his Solar panels full length :^
https://www.youtube.com/watch?v=WpATnkmKzYI
Quote from: Dave5Cs on July 08, 2021, 09:11:34 AM
Nope he is installing his Solar panels full length :^
https://www.youtube.com/watch?v=WpATnkmKzYI
So he is leaving the Unistrut exsposed on the roof
Yes, just like rivets and pop rivets.
I wouldn't attach or drill holes in the lap seam they are bad enough about leaking to began with ,when the membrane gets old and brittle
Many styles of Rivet nuts to choose from. I'm pretty impressed how strong some are. One video shows a guy who keeps cranking a machine bolt down wondering how tight it will go. Kept turning until the he twisted the head of the bolt. Not an ad so, I'm assuming it was not an altered bolt.
I'm feeling a lot better that this will hold up fine. Thinking I will cut four inch lengths of aluminum flat stock for a riser to keep the strut off the surface of the rooftop. Then 3 rivet nuts going through the strut, plate, and rooftop material will hold them fine. Place one every 16" or so. without any calculations or bench testl hard to know how much force the rails will hold but a lot more than what I tried earlier. LOL
Quote from: luvrbus on July 08, 2021, 07:32:57 PM
I wouldn't attach or drill holes in the lap seam they are bad enough about leaking to began with ,when the membrane gets old and brittle
I'll have to think about that since the tradeoff is there is double roof material and also potential for drilling into the cross-member for maximum strength.
I'll need to go look at how the lap is done but one would hope just like shingles they would have put the upper lap over the lower one as it curves over the side minimizing leakage if that is the concern.
Well, that was quick. The overlapped areas are cross ways, the bulk of where the strut will be mounted is single layer so no concern on leaking from lapped material. At those junction. I could not place any rivet nut there.
You need to make some calculations on runs that long,if you over do it attaching the Unistrut and don't allow for expansion and contraction you could end up with a mess like some of the schoolie crowd did
It would be easy to do that run in several sections with 1/2 inch gaps at the section ends..>>>Dan
Seems like a whole lot of work as we just mounted our panels individually but our system is a small supplemental one @ 100w/panel x 5. I know you guys are running bigger systems with much larger panels. We're delighted not to have to worry about keeping batteries charged while boon docking...
Quote from: Utahclaimjumper on July 08, 2021, 09:14:16 PM
It would be easy to do that run in several sections with 1/2 inch gaps at the section ends..>>>Dan
Buses move around a lot that is why they have lap joints and use a 1/2 dozen different type rivets
You might be able to find or have formed up some telescoping sections to slide inside your unistrut. That way the sections could shrink and grow with heat and not buckle anything. Bolt one end and let the other float. Those plates might work but I'd do two things. Make sure there is a good durable sealant between the plate and the roof, and also countersink the bottom of the holes so it isn't sitting on the flange of the rivnut. No wait, you said you were putting the rivnut in from the top of the plate I think. In which case I think it might be good to put a little sealant on the rivnut before it goes in the hole also, and then use those sealing washers. Maybe even some sealant on the threads.
Also, use rivenuts with a generous flange and get the most heavy duty rivnut tool you can manage. Probably something with long double handles or pneumatic. And then learn to use them without applying so much force you break things. Aren't Huck fasteners available in a rivnut style? If they are that would probably be your best bet. The biggest challenge with rivnuts is getting them secure without damage but tight enough to not slip. And sometimes the screw or bolt does not go in as easily as the mandrel comes out and spins the rivnut. In some cases it's necessary to chase the threads with a tap and use anti-seize to get a good solid connection. So everything that can be done to insure the rivenut is well seated and the fastener screws in with the fingers should be done. Of course if it fails you can always drill it out and start over but if it wants to spin you might end up doing that with a die grinder and trying not to nick the sheet metal. Which is kind of a pain.
Jim
We've installed lots or various size rivnuts without ever using the dedicated tool. We use a small flat bar that come with some rivnuts and insert the proper size bolt through it - tighten the bolt down with a battery impact then remove the bolt to take away the flat bar tool & move on. It's worked great without issue FWIW
Thanks for all the tips. This group is awesome, lots of knowledge and willing to share.
I'm going to make the lengths of struts 6', the length of two panels on the short side. That will eliminate any expansion issues. Next aluminum flat bar to raise the struts off the roof, allowing for air and water flow. Three sets of rivnuts mounted through a washer, strut, riser plate, roof. Several ways to seal hole, tbd. Then bracket to secure PV panel to unistrut. Easy to install and strong enough. lol
use aluminum unistruts to equalize expansion.
how much of an issue using steel channel on 5 foot length? still need aluminum? getting quote now but i suspect more money.
personally, I would use aluminum with aluminum roof panels for comparable expansion plus no rust issues. Small increase in cost compared to cost of rest of system and better for heat dissipation from panels.