Bolt hole sizing for thick connection

[jdonville]

I will be connecting a hook fabricated from 3-inch plate to a 9x5x0.5 RHS using a bolted connection. The 3-inch thick piece will fit inside the RHS and shim plates (holes, not fingers) will be inserted on both sides between the 3-inch piece and the webs of the RHS, so I can snug-tight the bolts without warping the RHS.

The dimension between the faying surfaces of the nut and bolt is 5 inches.

As I plan to use 1-inch through bolts, I am concerned about fit, especially with so many plies (2 webs of RHS, 3-inch plate, 2 shim plates).

AISC indicates that for bearing-type connections, which it seems to me this is, oversized holes should not be used in the main members. I would imagine that the holes in the shims could be oversized slightly as they are only there to permit tensioning of the bolt. I am reluctant to specify slotted holes as that would mess up my moment resistance calculations.

Anyone have any confirmatory or contrary advice or can point me to references?

Jeff

 

[KENAT]

If you're just looking at how to calculate the sizes required look in the back of ASME Y14.5M-1994. Appendix B gives calculations to help you with this.

However they make use of positional tolerance which I don't believe is as common in structural type stuff.

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

This sounds to me like the sort of design that is very likely to not get made the way you draw or design it.

It will be very difficult and time consuming to get ***exactly*** the right thickness of shims in place.

You will have a difficult time controlling the flatness and co-planarity of all of the surfaces.

There will almost certainly be non-uniform contact, which means non-uniform contact pressure and possibly deformation of something when the bolts are tightened.

Even if you could control all of these things to an acceptable degree at initial assembly, at some point it will be taken apart in the field, and there is just no way to even guess at what it will be put back together as.

I suggest that you reconsider the design concept.

 

[csd72]

Can you transfer the moment by bearing on the inside of the walls of the tube and just use the bolt to stop it sliding out?

 

[jdonville]

We have a milling machine that can reduce the shims thicknesses as required to get it close enough to where we need it to keep the RHS wall from deforming during tightening of the bolts.

The assembly is not intended to be taken apart once it is assembled.

The bolts will be snug-tightened only - not a slip-critical connection. The bearing on the sidewall/web of the RHS is designed to be less than yield at twice the computed static load.

As we will be drilling the holes ourselves, and the structure will be used exclusively by us, we have a lot of incentive to take our time and get them right, position-wise.

The holes in the shim plates will be oversized, as they are not required for bearing.

Anything further?

Jeff

 

[MintJulep]

Ok, so it's a pin joint.

Can you do it with a single bolt?

With multiple bolts in clearance holes you'll never really know the load path. Certainly it will not be equally shared amongst the bolts - until something yields and every gets into full contact.

Otherwise, make everything one size smaller, and clamp it together for fit. Ream and press in an appropriately sized spring roll pin in each hole.

 

[SnTMan]

I'd drill'em 1 1/8

Regards

Mike