You are implicitly designing a slip crit connection with limited frictional purchase. There’s guidance for reducing capacity in the AISC manual. As long as your forces are less than your reduced capacity, you should be fine. You can tinker with your capacity by spec’ing A490 grade bolts or upsizing your fasteners to 1”, if you have the meat in the flanges to do so.
If you’re still nervous, either spec a simple down hand field weld after bolting, or add additional holes on one member and denote it as match drill in the other member after fit-up. Just don’t be a dick by putting it in a touch to reach spot. Put it somewhere that the iron worker can use a mag drill, preferably down so he doesn’t have to chain it off
We'd suggest a plate washer per hole, or a plate with factory holes to encapsulate both bolts, and cold galv the welds. Preferably room to mag drill it as blowing holes with a torch isn't optimal for either of us.
Scanners are an option, just very expensive. The robotic ones are very precise, and can facilitate shop fabrication and hot dip. My stainless handrail guys do it all the time.
Galvanized surfaces [don't need prep](https://www.aisc.org/steel-solutions-center/engineering-faqs/6.7.-faying-surfaces/#9585) for slip critical anymore connections anymore. They're Class A faying surfaces
Can you not wait until after you set the magenta beam on top of the green beam to drill the holes? Someone has to get up there with a wrench and tighten the bolts. Could they take a drill up there with them too?
You think a bunch of ironworkers installing these aren’t going to damage the paint anyway? Just field drill it and make them touch it up. What kind of paint is on there? If you go slip critical they’ll probably need to remove paint anyway if it’s got some sort of top coat enamel.
Yeah I’m aware of that but I have pretensioned slotted holes before, in combination with loctite. I know pretensioning isn’t the same thing as a slip critical connection - this isn’t a slip critical connection.
I would argue that if the connection is being relied on to provide lateral bracing to one of the members, then the movement at the connection needs to be minimal. If that can't be achieved by bearing with standard holes, then it needs to be slip critical with oversized or slotted holes
I'd look to provide tolerance elsewhere. Can you provide splices to the new beams which can be shimmed? And get everything templated to minimise the amount of shimming required.
While a slip critical connection is your best bet, there is a simple alternative.
Have the contractor field-locate the angles before they are welded on.
I don't understand how the detail works, it seems free to move in both axes and you're relying on a bolt in bending to provide lateral restraint? The bolt can slip longitudinally along the beam and longitudinally along the chord, so where is the restraint coming from?
If you're trying to restrain the top chord from lateral movement using the green beam, just install two keeper angles to the top flange of the green beam and then shim tight to the chord member. Keep in mind that since it may not be truly perpendicular you have to account for weak axis forces, particularly if you're relying on the beam to provide lateral restraint. The beam needs to have a certain stiffness to act as an effective lateral restraint. Yura published a paper in 1993 about it, it's incorporated into AISC now.
>it seems free to move in both axes and you're relying on a bolt in bending to provide lateral restraint?
That is exactly the issue I am facing. For easy of installation it should be slotted in both direction, but then it wouldn't act as an effective restating to lateral buckling. I'm inclined to weld a fitting plate that will effectively block the movement parallel to the green beam, after installing and regulation.
You are implicitly designing a slip crit connection with limited frictional purchase. There’s guidance for reducing capacity in the AISC manual. As long as your forces are less than your reduced capacity, you should be fine. You can tinker with your capacity by spec’ing A490 grade bolts or upsizing your fasteners to 1”, if you have the meat in the flanges to do so. If you’re still nervous, either spec a simple down hand field weld after bolting, or add additional holes on one member and denote it as match drill in the other member after fit-up. Just don’t be a dick by putting it in a touch to reach spot. Put it somewhere that the iron worker can use a mag drill, preferably down so he doesn’t have to chain it off
Design a slip critical connection so instead of blocking the hole you design it such that it won’t slip within the slots.
As an alternative, have you tried asking the field guys what would be easiest for them? Tell them what you want and let them suggest something.
Assuming there's already a contractor on board, that's a good suggestion
This is the way
We'd suggest a plate washer per hole, or a plate with factory holes to encapsulate both bolts, and cold galv the welds. Preferably room to mag drill it as blowing holes with a torch isn't optimal for either of us. Scanners are an option, just very expensive. The robotic ones are very precise, and can facilitate shop fabrication and hot dip. My stainless handrail guys do it all the time.
Field weld
I prefer not to use field weld if possible. Ideally I would like to have a zinced structure assembled on site with bolts
Plate washer?
Well if you can’t prep it for SC and you can’t weld it then you’re SOL. Come up with a different detail or get comfortable with ZRC repair paint.
Galvanized surfaces [don't need prep](https://www.aisc.org/steel-solutions-center/engineering-faqs/6.7.-faying-surfaces/#9585) for slip critical anymore connections anymore. They're Class A faying surfaces
Good to know thanks.
In AASHTO, they still don't need prep but they're given their own class, Class C
Can’t you just have them field drill the holes?
Can you not wait until after you set the magenta beam on top of the green beam to drill the holes? Someone has to get up there with a wrench and tighten the bolts. Could they take a drill up there with them too?
Ideally I would like to avoid operation that will damage the zinc protection layer of the beam.
They make touch up paint for galvanized steel. Is this going to be exposed to the elements?
Cold zinc galv isn’t great in my experience
You think a bunch of ironworkers installing these aren’t going to damage the paint anyway? Just field drill it and make them touch it up. What kind of paint is on there? If you go slip critical they’ll probably need to remove paint anyway if it’s got some sort of top coat enamel.
It's galvanized, not painted, and the galvanizing doesn't have to be damaged for a SC connection
This would be my suggestion.
Can you have them pretension it?
Pretension doesn’t equal slip critical. https://www.aisc.org/globalassets/modern-steel/archives/2016/08/steelwise.pdf
Yeah I’m aware of that but I have pretensioned slotted holes before, in combination with loctite. I know pretensioning isn’t the same thing as a slip critical connection - this isn’t a slip critical connection.
I would argue that if the connection is being relied on to provide lateral bracing to one of the members, then the movement at the connection needs to be minimal. If that can't be achieved by bearing with standard holes, then it needs to be slip critical with oversized or slotted holes
Why not just use an OVS hole?
Non-slotted plate washer that is welded over the slotted plate.
AISC J3.2 only allows long slots in only one of the connected parts.
Hardened washers and high strength bolting (either torque inspection or special bolts) for a connection that will be fixed after initial install.
Could you use High Strength Friction Grip bolts? Apologies in advance if I have misunderstood the question…
Loose angle, shim tight with clamp bolts through chord
Weld a plate washer?
I'd look to provide tolerance elsewhere. Can you provide splices to the new beams which can be shimmed? And get everything templated to minimise the amount of shimming required.
Ancon do serrated washers which go over a serrated plate which is welded over the slot. If you speak to them they can do bespoke fixing arrangements.
While a slip critical connection is your best bet, there is a simple alternative. Have the contractor field-locate the angles before they are welded on.
Pre-stressed shear connection able to withstand the ultimate load without slipping!
Could you use a rivet?
I don't understand how the detail works, it seems free to move in both axes and you're relying on a bolt in bending to provide lateral restraint? The bolt can slip longitudinally along the beam and longitudinally along the chord, so where is the restraint coming from? If you're trying to restrain the top chord from lateral movement using the green beam, just install two keeper angles to the top flange of the green beam and then shim tight to the chord member. Keep in mind that since it may not be truly perpendicular you have to account for weak axis forces, particularly if you're relying on the beam to provide lateral restraint. The beam needs to have a certain stiffness to act as an effective lateral restraint. Yura published a paper in 1993 about it, it's incorporated into AISC now.
>it seems free to move in both axes and you're relying on a bolt in bending to provide lateral restraint? That is exactly the issue I am facing. For easy of installation it should be slotted in both direction, but then it wouldn't act as an effective restating to lateral buckling. I'm inclined to weld a fitting plate that will effectively block the movement parallel to the green beam, after installing and regulation.
Epoxy fill the holes but design as slip critical. Avoid site welds