Bolted moment connection
Bolted moment connection
(OP)
You designed a beam carrying a UDL as fixed end connections. The shop drawings show the flanges of the beam bolted with a clip angle and welded to the column. (Typical right?). Now given that the holes are larger than the bolts, the ends will rotate if slip is not prevented. You compared the possible rotation of the ends to the rotation of a simply supported beam,( WL^3/24EI), and found that the rotation due to slip is larger. Means the beam is really a simply supported not a fixed- fixed one. What would you do?






RE: Bolted moment connection
first, your rotation assumes the beam is free to deflect. on installation you would have a shear load path (friction), so i think your rotation is conservative, but we don't want to bet on friction.
could you use oversize bolts ? presumably you have enough flange width for the oversize holes that exist.
or you could bush the holes back to their BP dim'n.
or you could add more fasteners with the proper size holes, and the original fasteners would be somewhat redundant.
RE: Bolted moment connection
RE: Bolted moment connection
i visualise that you're considering that the top flange can displace 1mm and the bottom flange displaces 1mm in the opposite direction, thus creating your slope. i think this is highly conservative.
how about calculating the couple required to represnet hte end moment, and see if it is reasonable for this to be carried in friction (between to clamped surafaces) ?
do you have more than one bolt row on a flange ? multiple rows of fasteners would create another loadpath for the moment.
RE: Bolted moment connection
If the rotation needed for a simply supported beam is less than what a possible slip will provide, then if the beam was designed as fixed-fixed,(for less positive moment), then this is not conservative. Or am I missing something here?
My question is general. Clearly, the fabricator would provide a number of bolts to satisfay the required end moments. The problom is with the clearance and the possible slip.
RE: Bolted moment connection
RE: Bolted moment connection
The clip angles will not give you the stiffness of a fixed end condition unless they are temporary and it is intended that the connection be welded. For fixed ended conditions, I usually use a welded end plate type of connection. with slip critical bolts. Occasionally it is necessary to use steel shims to take up the slack required for placing the member.
Dik
RE: Bolted moment connection
But to make it a better simple connection, can you just put in a simple shear tab (bolted or welded)?
Mike
RE: Bolted moment connection
RE: Bolted moment connection
RE: Bolted moment connection
If it was designed as a fixed end then it should be detailed as a fixed end. The fabricator should change their detail. Is it too late for that?
RE: Bolted moment connection
RE: Bolted moment connection
RE: Bolted moment connection
I'm not sure that the code even requires the bolts to be slip critical (i.e. is the load reversal "significant"?).
RE: Bolted moment connection
RE: Bolted moment connection