slotted holes

[newbiengineer]

can someone please check if my wording is correct for slotted holes, and feel free to revise it:


Bolting shall be snug tightened (do not torque). Burr threads after nut is in place to prevent back-off.

 

[civilperson]

Your words are good, your design is suspect. Bolts in bearing only work for slotted holes perpendicular to the load.

 

[ChipB]

Personally, I've always used the word "Score" in lieu of "burr". Just a matter of preference I'm sure.

Civilperson is correct.

 

[rb1957]

is "burring" (or "scoring") standard practice ?

why not lock-nuts, or double nutting, or even lock-tite ?
maybe witness marks ??

 

[WillisV]

I use the word "mar" instead of burr.

 

[hogan666]

deform

 

[structuresguy]

As others have said, there are several similar terms that cna be used. You may or may not have to explain the situation to the steel erector. Usually, I like to put a descriptive note if I am requiring some special condition where I want, say, finger tight bolts in slotted holes, so that I can clearly explain the intent of the connection (ie to allow slippage in one direction). Otherwise, if these are standard shear connections in slotted holes, I don't think you really need to make them mar the threads in a snug tight condition. Usually it's only in finger tight condition, or if you have some vibration concerns.

I'm not sure why some of you guys are claiming his design is suspect. There is certainly no reason to suggest this. There are many cases where you want snug tight in slotted holes, both perpendicular and parallel loading. Given that he has not described his loading and intended restraint conditions, I think you have done a disservice to the OP by questioning his design ability. Rather than make a negative statement, why not ask what is the intended use? And then add constructive criticism if required.

 

[ChipB]

Sorry, should have been more clear.

I wasn't trying to say his design was "suspect". I was meaning civilperson is correct in that you want the slots perpendicular to the loading.

In civilperson's defense, newbie is trying to figure out a lot of things when it comes to understanding structures. I'm sure he was trying to keep him on course.

Newbie:
NEVER EVER EVER, use floor grating to account for LTB bracing of a beam. Right now, as a new engineer, you're okay asking that question. Now you know.

 

[ChipB]

Oops, sorry Newbie. I thought you were the one asking about floor grating a few threads back.

Again, I apologize.

 

[civilperson]

Structuresguy,
What is the use of snug tight in slotted holes with parallel loading?

 

[structuresguy]

There could be many applications. For instance, bottom chord of a truss with holes slotted in axial direction of truss. Don't tighten bolts until dead load in place, then snug tight bolts. Will allow it to slip, if it really wants to. This way, bolts are in bearing for shear, but as they are not fully tightened, the joint could still slip before a significant load is acheived.

 

[nutte]

Structuresguy, in your scenario, there is no parallel loading, as the connection is allowed to slip.

I don't think there are any valid applications for a snug tight bolt in a slotted hole with load parallel to the slot. There is no capacity for this connection, since the bolt is not fully torqued.

 

[Lion06]

I don't think he was looking for capacity parallel to the slot. He was probably just looking for capacity perpendicular to the slot, but using the slots as an expansion joint of sorts. That isn't all that uncommon, though I wouldn't use that detail for an expansion joint. That being said, there are details where you want to restrain translation in one plain, but not in another. Slotted holes achieve that purpose, but you have to make sure that the bolts can actually slip, which it sounds like he was trying to do.
I say to damage threads.

 

[nutte]

What is the use of snug tight in slotted holes with parallel loading?

This is the question Structuresguy responded to, and which my comment addresses.

 

[newbiengineer]

i just want an opinion with the word "burr" seems like seems like there are other words to use..

no need to suspect my design.. structureEIT is correct.. am using it for expansion.. as far as perpendicular to the load, shear capacity of bolt, plate bearing, etc is ok..

thanks for all your replies..

 

[newbiengineer]

correction: perpendicular to the slot

 

[ChipB]

When I was an Engineering Manager at a steel fab shop, I saw long slotted vertical holes in the beam shear plate with short slotted horizontal holes in the clip angles of stair stringers. When I asked the EOR for the project about it, he stated the stairs were going to a concrete pad at grade, and the connection acted like a partial pin, allowing slight rotation of the stringers with the vertical movement of the concrete pad at grade due to freeze/thaw cycles. In my head, I rationalized it out to be basically an inclined/roller support, just so I could sleep at night. It made sense, but I'd hate to try to back it up with the numbers.

It is still standing as far as I know.

 

[structuresguy]

I don't think there are any valid applications for a snug tight bolt in a slotted hole with load parallel to the slot.

Ok, maybe I should clarify myself. In my example, i was not trying to resist a load parallel to the slots. I was using it as an example, as others mentioned, of a case where the slot in snug condition could be used to relieve a connection of undesired loads in one direction, without it necessarily being a true sliding joint. If I wanted a true sliding joint, I would use double nuts, with connection only "finger tight" and UHMW plastic low friction bearing pads, etc....