How Strong Are Rivet Nuts?

[Scooter]

Question for the Pelican brain trust:

I am installing a TRE roll bar like the one pictured below, along with the B pillar mount. I would like to install the front foot pad as low as possible, which means I would rather not weld in the mounting plate. One option/question is whether an industrial strength rivet nut (pic below) is strong enough to mount the front foot or not? My initial thought is no way, but I have seen steel rivet nuts used in some pretty strong applications.

I ask that your responses please be kind and courteous, as I am a very sensitive person.

*Pics are sourced from an old post from fellow Pelican ja78911sc. My installation will be in a Targa.

[john walker's workshop]

pop rivets would be easier. same material isn't it?

[Bob Kontak]

Originally Posted by john walker's workshop

pop rivets would be easier. same material isn't it?

Al-u-minium would be the fastest.

The rivets appear plenty strong. But I have no business giving a yay or a nay.

Environment Rules Joint Design

[aschen]

they are pretty strong, though I am in not position to quantify this strength

I think the problem is the joint can only be as strong as the material captured by the ridges of the installed nut.

I would expect the rivnut could be pulled out of the relatively thin sheet metal of the car with out damaging the actual fastener.

The shear area for pull out of the fastener should be nearly equal to the circumference of the nut times the sheet metal thickness


I guess an easier way to say it is it wont be any stronger than bolting from behind without a backing plate

Aschen is an engineer but has no real experiece with this

[Scooter]

Originally Posted by aschen

I would expect the rivnut could be pulled out of the relatively thin sheet metal of the car with out damaging the actual fastener.

I was thinking the same thing. IF the rivet nut is strong enough, it still may pull through the sheet metal.

[Discseven]

Dear Scooter,

With much respect & admiration, and treading as lightly as possible, I humbly suggest this cage fasten be considered in light of what speed you might be rolling and/or crashing about at. With no knowledge whatsoever of the sheer strength of the intended rivets, I shall all the same say the rivet idea... easy now ... blows (assuming you might roll/crash at any significant speed.) My vote is cast for heavy duty industrial weld. Your life is worth... a good f'in weld.

[mspirito]

Agree

[ClickClickBoom]

Well outside of the intended use for RivNuts. 8.8 bolts with a backing plate at the minimum. I've built more than a few roll bars.

[Scooter]

I appreciate the opinions.

I am really looking for somebody to give me an idea of the strength of a rivet nut. They use rivets in the aviation industry, so they must be strong, but how strong?

[Jack Stands]

I think any racing sanctioning body would give you the same answer - not strong enough! Do it correctly, it's your life hat could be saved.

[Scooter]

Thanks ClickClickBoom.

BTW: I should have said in my original post that I was not likely to use the rivet nut idea, but I am still very curious as to strength.

I should note that I am seriously considering welding the bar directly to the sill. The weld-in plate would be nice to be able to remove the bar, but I like the alignment without the added plate.

[Jan J Skibinski]

Rivet nut not strong enough for several reasons. The rivet nut will pull through the hole drilled into the steel attach point. The hole itself weakens the the attach point allowing a fitting to pull through. If you use the rivet nut use one that is keyed. Meaning there is a small "tang" on the underside of the top flange of the rivet nut and requires that a notch be filed out on the edge of the drilled hole in steel. Otherwise non-keyed rivet nuts can rotate with bolt captured in it making removal a lengthy ordeal. Rivnuts (actual product name) are mainly used for non-structural fairings (on aircraft for instance) and joining non structural thin metals.
Hard knowledge gained from working on airplanes , (Porsche 356 and 911 and aircraft are only some of my bad habits.
Lenghty , but hope it helps your decision.

[Scooter]

Thanks for your input Jan.

[VW_NUTT]

Well speaking from experience with the strength of rivnuts. I had a 170lb cylinder of refrigerant strapped to the rear handle in my sprinter van that's held on with these. While going over a set of railway tracks I heard the bottle fall over. Opened the back door to see the handle and rivnut had pulled out of the sheet metal. There is no way of using a nut on the area where the handle was so I hammered it back in then welded it. So if a full cylinder that weighs 170lbs can rip it out I don't think I would trust my life on it.

[emac]

I'm not the expert but my thought would be they are only as strong as the material they are attached to
Ernie

[Steve@Rennsport]

Rivnuts would be totally unsafe in this application.

Those are OK for attaching non-critical parts to sheet metal, however roll bars need to be either bolted or (much) preferably welded to the chassis, otherwise they are ornamental objects.

[tctnd]

Ask yourself if you want to be thinking about this when your car is upside down at 98 MPH.

[ClickClickBoom]

Originally Posted by tctnd

Ask yourself if you want to be thinking about this when your car is upside down at 98 MPH.

This:
https://www.youtube.com/watch?v=epqSuvrBWQs

[HawgRyder]

To mount an approved roll bar...consult the NASCAR manual....or any racing body rules in the approximate class your car would race in if it were a race car.
They are very knowledgable from all the crashes they have had over the decades.
You would be surprised just how stringent they are....considering metal thickness...bracing backup metal...and the spread and size of bolts to secure the frame.
For weld in bars....you MUST overlay the area with thicker metal to spread the load...and besides that...you need thicker metal to weld to anyway.
My rule of thumb....do I trust the bar/cage if I were to drive ?
I hav seen whole cars disintegrate...leaving just the driver sitting in his protective cage....and walking away from the crash!
Bob

[Scooter]

Originally Posted by tctnd

Ask yourself if you want to be thinking about this when your car is upside down at 98 MPH.

Nooooooooo!