Thread Capacity

[jayrod12]

Hello Everyone,

I've searched previous threads and didn't come across the specific answer I was looking for.

I have a situation where we will be threading a ring bolt into the wall of a 1/4" thick hss. I have determined that the HSS itself can resist the load except for checking the threads for pull-out. The ring bolt also has the capacity I need but again am worried about the threads.

I know that if I could provide enough thread depth that the capacity would be strictly based on bolt capacity however that is not a feasible option. I was wondering what references people had here for determining the capacity of the threads.

The ring bolt will be loaded in pure tension only with a load of 5 kips. The HSS is a 6"x4"x1/4" with the threaded hole being drilled into the 6" face.

Any help on references would be great.

Thanks,

Jared

 

[JLNJ]

I would be hesitant to put any real loads into a drilled and tapped hole, though I don't know of any guidance from AISC on this matter. Too many variables, too little redundancy.

How about a hollo bolt?

 

[msquared48]

Or welding a Nelson Sill late Anchor to the side of the HSS and screwing the ring bolt (different configuration now) to the Nelson Stud?

Mike McCann
MMC Engineering

 

[madmantrapper]

What size threads are you talking? Could you drill through and put a nut on the other side?

 

[CANPRO]

Can you weld a small plate on the face of the HSS in the area where the hole is to be tapped and then tap the plate and HSS? You can size the thickness of the plate to engage as many threads as required.

You could also weld a nut on the face of the HSS, but from what I've read on this website, welding nuts to structural steel isn't acceptable practice.

 

[TLHS]

Here are a couple of threads about it.

http://www.eng-tips.com/viewthread.cfm?qid=290559

http://www.eng-tips.com/viewthread.cfm?qid=35222

Alternatively if you're somewhere where you can still weld an attachment, just use a weld nut to give yourself a threaded attachment point. There are a million types out there and there is likely a configuration that will do whatever you want it to.

 

[jayrod12]

Unfortunately due to architectural reasons (go figure) there is no way to weld a bolt or a piece of steel to the face of the HSS. Further the HSS is already fabricated and installed so we cannot provide anything on the inside face either.

I'm going to take a look at those threads as well as a hollo bolt (??)

Is it unreasonable to rationalize that since a nut provides 3/4" of thread depth and my HSS is 1/4" thick that I would have something slightly less than 1/3 of the tensile capacity of the bolt?

 

[jayrod12]

Unfortunately due to architectural reasons (go figure) there is no way to weld a bolt or a piece of steel to the face of the HSS. Further the HSS is already fabricated and installed so we cannot provide anything on the inside face either.

I'm going to take a look at those threads as well as a hollo bolt (??)

Is it unreasonable to rationalize that since a nut provides 3/4" of thread depth and my HSS is 1/4" thick that I would have something slightly less than 1/3 of the tensile capacity of the bolt?

 

[jayrod12]

Nevermind, Thanks TLHS, between those two threads I got the answers I needed.

And those Hollo bolts are quite interesting

 

[XR250]

Seems like a lot of load to be putting on the 6" face of a 1/4" tube. Are you sure it can take it?

 

[LittleInch]

At some point here you need to take a sense check. You're talking about a force equivalent to a SUV hanging off an eye bolt held only on a 1/4" plate??. You can do all the calcs and theorising you like but it just doesn't sounds right to me. What is the consequence of failure of your bolt? Would you sleep under it?

Why can't you add some depth to the back of this plate if it's attached to a wall where no one will see it?

The relative depth argument needs to be treated with care and a healthy safety margin allowed. Either that or just get a few samples tensile tested. Much cheaper than the law suit you might end up in if it doesn't work.... Would also demonstrate to the architect that his idea doesn't work.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[oldestguy]

When I have come across this sort of thing, I take an equivalent bolt, threads and plate and actually do a pull out test to see what the ultimate is. Usually very surprising.

 

[jayrod12]

Thanks all for your concern.

In the end we are not going to encorporate this detail (for a multitude of reasons but mainly the lack of redundancy in the system). The intent was to use them as travel restraint/fall restraint type tie-offs. We have convinced them to go with a continuous tie-off rail around the building perimeter with connections that are more robust and with significantly more redundancy if local failure were to occur.

From the get-go I was not comfortable with the design and noted my concerns however was told by a superior to try and make the eye-bolts work comfortably and in the end could not get a reasonable solution.

I much prefer the new framing option.