Capacity of Bolts in Tapped Holes 2

[countervail]

We are tapping holes in a hollow section to allow us to fix in a set of bolts. Is there any guidance on how to calculate shear and tensile capacities for bolts in tapped holes?

•The wall thickness of the hollow section will be less than the nut thickness, so I would expect a reduction in capacity.

•The wall material will be of a lower grade than the nut, again I would expect a reduction in capacity.

I am working in the UK but any pointers to codes “US or Australian etc” that have helpful guidance would be appreciated.

Thanks

 

[bridgebuster]

See if the attached is useful.

 

[hokie66]

Bridgebuster's reference does the tensile capacity check. For shear, it is a bolt with threads in the shear plane, and you have to check the bearing on the hollow section wall.

 

[TLHS]

Once or twice I've needed to prove that a tapped hole was sufficient, but didn't need exact values. In those cases I've taken the tabulated values from the Steel Handbook and applied reduction factors for the difference in thickness between the standard nut and the tapped material, and for the difference material strength between the standard nut and the actual tapped material. Then I applied a *very* healthy additional safety factor on top.

I was basically only comfortable doing this because we were installing systems that were identical to existing and wanted to prove to myself that they worked. The resulting factor of safety that popped out using a practical bolt pattern was huge, so it wasn't worth the time to go into a more detailed analysis.

For actual structural applications where life safety is an issue I'd be pretty wary, personally, of using a non-tested tapped connection unless it had been significantly overdesigned and included some additional redundancy. If it's just a hold down connection for a piece of equipment that keeps it from vibrating across the floor or something, I might be open to it.

 

[RacingAZ]

Why not just use one of those expansion type bolt specifically designed for hollow sections, like a lindapter hollo-bolt?

 

[countervail]

Thanks chaps, your advice (especially Bridgebusters) was exactly what I was looking for.