Need Help Lighted Box Sign Mounted With "unistruts"

[KevinRBeard]

Greetings.
I am installing a 10' x 7' lighted box sign on the side of a prefab metal building. The only installation instructions say to "use 1/2" thru bolts and unistruts". Well, that's helpful! Looked for help on the internet but no go.

Is there anyone who can explain what this means? The sign is around 350 lbs. Need help!

 

[joeb]

Unistrut is a U shaped channel from which very heavy things can be hung

 

[signbrad]

The unistruts go on the inside of the building walls to provide something to attach the through bolts to. This spreads the load for the attachment points.
That's my guess.

Skimpy instructions, if you ask me.

 

[Billct2]

Yep, when you're in a box store look up at the bar they hang HVAC and similar equipment with. It's a heavy duty slotted channel. We get it at a industrial supply house like Grainger Strut Channel - Strut Channel and Accessories - Grainger Industrial Supply

 

[KevinRBeard]

Thanks everyone for your replies. I did know what a unistrut was, more wondering how they are used. The question is are they simply bolted to the inside of the metal sheeting to distribute the load across the metal? Don't want to screw this up. Any suggestions?
Skimpy instructions indeed!

 

[spectrum maine]

angle iron will do the same thing.

 

[Billct2]

It's a way distribute the load across the surface instead of nuts & washers pulling on one spot. So depending on the bolt pattern you may use a 6' length vertically to hold three bolts.
And spectrum is right, an length of angle iron will serve the same purpose.

 

[signbrad]

I agree. Angle iron would work fine. I have even used 2x6 lumber. Unistruts have holes already, theoretically making the job easier. I think you can get them with slotted holes, too, which may be even better. And a 12 or 14-foot Unistrut installed vertically may span more than just two horizontal framing members.

 

[signage]

Why do you even talk about the holes, the nuts that fit the channel would the same thing. The strut just spreads the load over a larger area.

 

[KevinRBeard]

What I'm going to do is
1) Remove the face
2) Lift the box sign into place
3) Use a 2" metal post (w / holes) behind each exterior vertical edge to hold the sign away from the corrugations in the metal.
4) Line up matching metal posts (both sides) on the interior and bolt through in several places
Whatcha think?

 

[spectrum maine]

hang sign directly against corrugated wall - slam a few large tek screws w/ large washers 1/2 over the extrusion in the back, then thrubolt it into the unistrut. the teks will temporary level it. or mount angle clips on wall to unistrut- hang sign , face & all, then use large teks to hold sign on clips. easier than flying a 20' face after the fact.

 

[signbrad]

Why do you even talk about the holes, the nuts that fit the channel would the same thing.

Good point. You would certainly have a cleaner look from the inside if you did it this way. All you would see is the back of the strut. But if, on the other hand, you through-bolt the strut, the hardware is visible from inside the building. Using the nuts that fit the strut means tightening must be done from the sign side, which means careful length selection of the screw. If you're using stud bolts (threaded rod) rather than a cap screw, length is not as crucial, as a too-long stud can be concealed inside the cabinet, assuming your mounting clips are inside.

 

[signbrad]

What I'm going to do is
1) Remove the face
2) Lift the box sign into place
3) Use a 2" metal post (w / holes) behind each exterior vertical edge to hold the sign away from the corrugations in the metal.
4) Line up matching metal posts (both sides) on the interior and bolt through in several places
Whatcha think?

Are you wanting to pinch the cladding (corrugated siding) with the vertical posts, rather than reach through the cladding with bolts to horizontal structural steel members on the inside of the building? That seems like a lot of weight to hang on sheet metal, but I don't consider myself an overly experienced installer. I have always tended to over-engineer an install just to cover myself.

Or are you just worried about crushing the corrugations when the sign is pulled against the building as you tighten bolts? Is that the purpose of the outside posts? I've never seen corrugation crushed but that doesn't mean it can't happen. Metal building construction varies wildly in quality.

My goals when installing signs on a wall have always been: don't rely on cladding or siding to hold a heavy sign. And hide fasteners, if possible. Obviously, these are not rules that cannot be broken. Much of sign installation is just common sense and experience. You are in the best position to make the decisions on your specific job since none of us have actually seen what you are working with. If you take extra steps to ensure a solid mount, especially if it's a cheaply built structure, there is nothing wrong with that.
I have seen more than enough cheap-ass installations in the last 40 years.

I remember a shop owner that hung some 4'x4'x1/4-inch aluminum plate signs at a major league baseball stadium. He instructed the fabricator to tap and thread blind studs into the backs of the panels. How many threads of each stud do you think were engaged? Maybe three at most? More than one person on his staff objected. But he insisted, saying that he was following the engineering specs. He callously claimed that if anything bad happened it was not his responsibility.
Luckily, when the first sign fell into the seats below, the stadium was empty.

Brad in Kansas City