Shear strength of setscrew calculation

[CRS51]

Hello all, could anyone work out the combined shearing force in tons of 6 off 7/8”UNC x 3 - 1/4” setscrews torqued down to 500 lb/ft ? They are grade 12.9 material.
I hope this makes sense, I would like to know the force in tons to shear the lot off in one go. They are holding a large bracket to a frame.
Chris

 

[Munkul]

Shear is different to tension with bolts. Relatively easy to shear a bolt sideways, much more difficult to stretch it in tension.

But given that the bolts were tightened, what you're wanting to know is the total clamping pressure, because whatever sheared it all off firstly had to overcome the clamping pressure.

You can work out the total clamping pressure fairly easily, working off empirical data for clamping force from torque, but this will be a best guess, as torque isn't very accurate. Then work out area of pad that's being clamped.

I had some tables for working out pipe flange clamping forces a while back... can't remember where though

 

[RonA]

Will this help?

https://www.boltsgalore.com.au/downloads/technical/Bolt%20Shear%20Strength%20-%20Imperial.pdf

RonA

 

[Rannsachair]

As @Munkul says bolts are normally designed to resist compressive or tensile loads rather than shear, probably best to include a sketch or photo to ensure the correct calculation is used.

 

[atomant48]

sounds like a bracket bolted to “the side” of something taking a vertical load ? Almost like two pipes connected horizontally via mating flanges and then one of the pipes taking a vertical load so the bolts all in shear (at least initially… :-)) a sketch might reveal all!

re reading munkuls reply looks like hes on it.

 

[AndersK]

To break one of them multiply core area with 1200. This is for tension. Use area in mm2 and you'll get the force in Newton.

If it's a true shear load multiply first calc with 0,8.

This is simple calculations that usually are good enough.
Want to be more accurate, FEA is required with contact analysis involved so not done by hand.

 

[CRS51]

Thankyou all for the replies, I will get a sketch up tomorrow.
Chris