Using Smaller Bolts in Misaligned Holes

[marinaman]

I have a project where I have some beams coming into a steel girder at a 45 degree angle.

The connections of the beams to the girder are all single plate bolted connections.

During the erection process, only one bolt was initially installed by the erector for each of the 45 degree beams. He was going to go back and install the rest of the bolts as he progressed in erection.

Now, when he went back to install the rest of the bolts into the single shear plate bolted connections, the holes are slightly misaligned to where he can not get the 3/4" diameter A325's installed. Due to the each beam's angle, and the stiffness of the surrounding members, he's not able to wrangle the steel to get the holes to align in order to install the bolts.

In brainstorming, the idea was floated to install 5/8" diameter A490's into the misaligned holes previously intended for the 3/4" diameter A325's.

In theory, the load capacity would be acceptable.

Has anyone done this before? I can't think of where this might be prohibited by the code.

I'm trying to explore all of my possible options. I do not want to weld this connection, as its geometrically too tight to get good weld where it would need to be placed.

Opinions appreciated.

 

[racookpe1978]

It is a 45 degree connection = The forces ARE going to try to force each connection point "sideways" across the new (very large) gap between the original holes and the undersized bolts. That will allow (over time) every 45 degree joint to slip significantly before loads get picked up through the 45 degree brace between the two larger structural members.

Instead - IF you cannot get the bolts through "backwards" (from the other side of the joint) because of length restrictions, insert a liner for each hole (1/16 thick) to fit between the 5/8 bolt - CHECK IT IS INDEED STRONG ENOUGH! - and the original bolt hole 9sized to be oversized for 3/4 bolts, right?) The liner should be the same yield strength as the bolts (or structural steel) and should be the "through length of the web + plate thickness" length of the connection so the liner picks up the shear stress and carries it to the bolt inside the liner.

 

[rb1957]

i don't think he can insert a bushing ("liner") in each hole ... the hole CLs are offset, making the hole into a figure eight; at least that's the way i read it.

installing a smaller bolt sounds pretty "naf" ... the bearing surface is now very small, not sure who'd sign for the drwg change.

for my money, open the holes up (change the figure eight to a circle) to take the next bigger size. hopefully you've got edge distance to allow this ?

more difficult ... install a thick bush in each hole, then drill thru a hole that'll leave some of the bushing wall behind (something like a 1/16") so instead of your suggested 5/8" bolt you might get a 1/2" bolt to fit ... maybe that was what the previous post had in mind ?



another day in paradise, or is paradise one day closer ?

 

[KootK]

I've never done this but your approach sounds reasonable Marinaman. Some things to consider:

1) you might need to revisit bolt bearing checks if the hole diameter is significantly larger than would normally accompany a 5/8" bolt.

2) if there is potential for load reversal, slip critical might be a desirable option.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[rb1957]

bearing of a 5/8" bolt in a 3/4" hole would be pretty high

another day in paradise, or is paradise one day closer ?

 

[marinaman]

Hmm.

Since the beams are coming in at 45 degree angles, and there are other beams installed, there is not room to drill out the holes to a bigger diameter and use a 1" bolt. My edge distances would probably work with that idea, but the erector just doesn't have enough room to get a drill in there to make that happen.

If the erector can't work this out and get my 3/4" diameter bolts in there, I'm leaning toward the 5/8" diameter bolts.

The members do have primer on them, but, I can get slip data from the fabricator on that primer material, consider 5/8" bolts, and consider them in a slip critical situation.

That's sort of the way I am leaning, but waiting to hear from the erector to see if he can get these bolts installed.

 

[LittleInch]

A drawing, sketch or photo would be good. How many bolts per joint?

Doesn't feel right to me.

My motto: Learn something new every day

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

 

[rb1957]

what would holmes do ? (no, not sherlock, but mike)

maybe hot rivet them together ? use a 5/8" slug and formed heads on both ends (so you fill the holes).

another day in paradise, or is paradise one day closer ?

 

[ztengguy]

Weld it.

 

[jayrod12]

what about welding oversized washers for the 5/8" bolt that are designed for the bearing.

 

[dhengr]

Marinaman:
Can you get a right angle motor and a reamer in there? We can’t see it from here.

 

[marinaman]

I thought I had a photo of this situation. I may have.....If I can lay my hands on it, I'll post it.

dhengr - Its just so dang tight in there, I can't get anything like that it there to help me out.

Welding - I really don't want to weld anything. The reason is, I start getting conflicted over the amount of rigidity in the end of the beam. If its welded, that baby is really rigid to the face of the supporting girder. If that's the case, I'd be essentially twisting the weld. I've run the numbers and I'd have to have a heck of a lot of weld to resist a wL^2/12 condition. I don't want to go that route. I'd like to stay with the pinned-end condition.

I'll try and hunt down a photo.

 

[KootK]

If the only objection is bolt bearing stress, I'd be inclined to let it go. Firstly, you've probably got twice as many bolts as you need for the actual load. Secondly, the expected failure for bolt bearing is probably the extra 1/8" deflection at the beam end required for the bolts to plow a bit and redistribute stresses. Ductility to the rescue.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

Don't sweat the fixity. You have similar issues even with the bolts. It's less than ideal but workable. If you can indeed weld, consider Jayrod's solution. It gets you back to bolted.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[Ron]

Agree with kootk....fixity is not an issue. I doubt you have fixity even with a welded connection. Remember...the structure will act the way the loads dictate....not how you analyze it.

 

[canwesteng]

I don't see how bearing is an issue because of hole size, steel around the bolt should yield in bearing and deform to the shape of the smaller bolt. S16 gives bearing perpendicular to long slots as 80% of the capacity of bearing, so if you want some piece of mind run a quick calc using that as your bearing strength and see if you aren't ok.

 

[oldestguy]

A good welder with a torch can do a neat job of "reaming" the plates, perhaps enough to get a 1" bolt in if needed..

 

[KootK]

Here's a rather extreme all bolted alternative. Certainly, just about anything would be more economical.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.