Slip Critical w/o Bearing?
Slip Critical w/o Bearing?
(OP)
The usual process with SC bolts is to design such that the service loads don't slip and the factored loads can be resisted in common bearing if necessary.
If the bearing mechanism is simply unavailable to you for some reason, do you have the option of designing your connection as slip critical for the factored loads? My gut tells me no but I figured I'd ask around before I abandon the idea...
If the bearing mechanism is simply unavailable to you for some reason, do you have the option of designing your connection as slip critical for the factored loads? My gut tells me no but I figured I'd ask around before I abandon the idea...






RE: Slip Critical w/o Bearing?
Look in AISC 7-24 through 7-27
RE: Slip Critical w/o Bearing?
I had a quick look at the S6 code and it is silent on that, but I seem to remember that the Eurocode gave you the posibility to design connections that way.
RE: Slip Critical w/o Bearing?
I'm curious, how can you have a connection where the bearing mechanism is unavailable?
RE: Slip Critical w/o Bearing?
I have a galvanized, existing HSS post that needs to have a fall arrest bracket fastened to it. The fabricator has detailed two 10 mm plates sandwiching the post. Four bolts connect the two plates. Unfortunately, the bolts are located to the sides of the post rather than passing through it.
I was hoping to justify the connection through SC friction. I'm nervous though. Some poor bastard WILL be hanging off this thing to wash windows etc.
Interestingly, the coefficient of friction is better for a prepped galvanized surface than it is for bare steel.
RE: Slip Critical w/o Bearing?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Slip Critical w/o Bearing?
RE: Slip Critical w/o Bearing?
Can you use AISC for this one design issue? Or can you just design the service level slip resistance (from your code) to be greater than the factored loads (and maybe provide an additional safety factor on it)?
RE: Slip Critical w/o Bearing?
You have two plates being clamped to an HSS with a gap between the bolted plies, I don't doubt that it will work, the zinc is soft and the steel will bite for a mechanical bond. The plates will bend a little, depending on the distance between the side of the HSS and the bolt, so most of the contact force will be at the corners of the HSS. Is there any chance it will crush the HSS?
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Slip Critical w/o Bearing?
RE: Slip Critical w/o Bearing?
If I understand this correctly, then I am with Paddington....not your typical SC connection.
RE: Slip Critical w/o Bearing?
RE: Slip Critical w/o Bearing?
But another solution might be to weld two bearing plates to the side of the column. Heck if you do that, why not weld the two plates to the column in the first place?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Slip Critical w/o Bearing?
StructuralEIT: I do have the AISC 13th. I'm comfortable with the process of designing a SC connection for ULS loads. I'm just not sure if the intent of the CAN code is to preclude solutions that rely soley on friction mechanisms, as a philosophical matter. I take it that you believe that it would be okay using AISC design philosophy?
Paddington: I agree, this is not typical SC. However, many of the same principles apply. The HSS may crush AND the plates may fail in bending. Both will have to be checked. On the plus side, the loads are very small. I hadn't thought of the bolt concerns that you mentioned. Can A325 / A490 not be galvanized? Could I go with SS bolts perhaps?
MSquared: To install a through plate, they would have to flame cut holes for it through the HSS. Wouldn't that be ticky on site? I'm leaning towards a welded solution, despite the associated galvanizing headaches. The fabricator galvanized the posts ahead of the brackets. They then didn't want to compromise the post galvanizing with the welding. That's why it wasn't welded in the first place.
RE: Slip Critical w/o Bearing?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Slip Critical w/o Bearing?
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Slip Critical w/o Bearing?
Either use welding as suggested above or use bolts in bearing. This can be done by drilling holes on site and reaming if necessary.
BA
RE: Slip Critical w/o Bearing?
They could use a mag-drill and cut-off wheels to make the slots. Cold galvanizing could be used after welding. There are procedures for welding galvanizing safely.
RE: Slip Critical w/o Bearing?
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Slip Critical w/o Bearing?
BA: I agree, this is not textbook SC. Similar principles still apply however. There are more things to check here of course. Most importantly, the bolt tension must be verifiable as turn-of-the-nut will not apply here.
Paddy: what is zinc galling and why dooes it necessitate lubricating galvanized threads?
As a general question: When a bolt is galvanized, what measures must be taken to ensure good fit with the nut?
RE: Slip Critical w/o Bearing?
Galvanized nuts are over-tapped prior to being galavanized.
The Bolt threads are standard threads.
The build-up from galvanizing is accounted for in the over-tapped nut.
RE: Slip Critical w/o Bearing?
http://www
"When zinc parts rub against other parts — particularly other zinc parts — galling (adhesive wear) occurs. The more rubbing that takes place and the greater the load, the worse galling becomes, and the surfaces tend to cling to each other. In the early symptoms, galling causes moving parts to hesitate, plungers to stick, levers to bind. Occasionally, they chatter as they stick, release and stick together again. This is the slip-stick tribological phenomenon. Eventually, part-to-part welding occurs and the mechanism fails."
As galvanized bolts are torqued, pressure between the thread surfaces increases. Most steel erectors know to make sure the lubrication is there, but the torque/tension ratio needs to be established in a Skidmore if you are trying for a predetermined tension.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Slip Critical w/o Bearing?
BA