Fitted bolt connections
Fitted bolt connections
(OP)
The fabricator wants to use bolted connections on a truss. There are a few connections where slip critical connections will not work i.e. we will need a lot of bolts. So I am trying to see if I can use a fitted bolt connection for these connections. We are using 3/4" diameter A325X bolts. What size of hole is required to ensure a fitted bolt connection? Is this addressed in the Steel Manual or any other reference text?





RE: Fitted bolt connections
BTW, slip critical is a joint designation, a requirement for very few connections, I think you mean High Strength Friction Grip bolts.
Timing has a lot to do with the outcome of a rain dance.
RE: Fitted bolt connections
Bolts are "X" when the threads are excluded from the shear planes and are only specified for bearing connections. Unless you are using thin material, almost all A325 and A490 bolts are X bolts because of the limited thread length.
You do not need fitted holes, 1/16" over the bolt diameter is the standard.
Bearing bolts in standard holes are normal in bolted trusses.
Once or twice, I have used the HFGBs for a joint where I needed the joint to be slip critical for one (service) load case and the higher bearing strength for another (extreme) load case.
Timing has a lot to do with the outcome of a rain dance.
RE: Fitted bolt connections
Thanks for the response. My concern was the 1/16" over bolt diameter space when using bearing bolts in standard holes. Will this 1/16" over dimension not cause the connection to "slip" and then the cumulative sum of "slip" in all the truss connections lead to unacceptable truss deflections? Or am I being over cautious?
Thanks again.
RE: Fitted bolt connections
Timing has a lot to do with the outcome of a rain dance.
RE: Fitted bolt connections
If for some reason the bolts are required to be tight in the holes, I would call them pins instead of fitted bolts. In that case, you have to specify the tighter dimensional control necessary to make tight pins work. I had a job once where a stayed and strutted awning structure at an airport required tight pins, the fabricator used tolerance holes, the columns bent to accommodate the pins, and the fabricator had to do a lot more work to straighten it all out. So it does happen.
RE: Fitted bolt connections
Timing has a lot to do with the outcome of a rain dance.
RE: Fitted bolt connections
Paddington, you must be older than I am. A325 bolts have been in relatively common use since about 1960.
RE: Fitted bolt connections
Timing has a lot to do with the outcome of a rain dance.
RE: Fitted bolt connections
Yes, they did emphasize the friction type connections in the early days of high strength bolts. Now, we rarely worry about slip in the connections.