Torsion on Steel Connections
Torsion on Steel Connections
(OP)
Can anyone point me to a good reference for find torsional force on steel connections.
I have bracket connections which will support longitudinal, lateral, and vertical forces. I am sure there will be torsion on my welded connection, but I am unsure how to find how much, because there are connections on either side of each and the load sharing, I would imagine, greatly reduces torsion.
I understand this is probably basic, but I am stuck.
Thank you
I have bracket connections which will support longitudinal, lateral, and vertical forces. I am sure there will be torsion on my welded connection, but I am unsure how to find how much, because there are connections on either side of each and the load sharing, I would imagine, greatly reduces torsion.
I understand this is probably basic, but I am stuck.
Thank you






RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
As a side note, I would not weld these connections if these are in fact runway beams. Typically bolts are used, with slots where the engineer wants to release the load. As the loads are large and cyclical, it's better to have a determinate load path. If the load path is indeterminate, the actual load path will vary based on stiffness. Typically this is not an issue, as steel has enough ductility to mold to our assumed load path, but overstressed welds cyclically overloaded are prone to cracking and brittle failure. Similarly, the runway beams are typically not made to be continuous, such that the structure is determinate and there is no worry about cyclically overloading members. I can share some typical details if you like.
RE: Torsion on Steel Connections
Probably. But it depends how stiff some of those "supports" are and what is beyond. For example, you have something going to the top flange and it is pinned supported (which means it is modeled as infinitely stiff relative to the beam's weak axis). Well, is that accurate? Because if it isn't.....that could change things. Same deal with that haunch support on the bottom flange.
That gets answered by considering what I discuss above.
RE: Torsion on Steel Connections
It was designed in the 1960's and I am analyzing it for a 5 ton upgrade to the overhead crane. Do you have a reference I can quote to show that torsion isn't significant? This was my hunch at first, but I don't feel that I can leave the torsion force on the welds as 0 without a reputable source to back it up such as AISC.
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
RE: Torsion on Steel Connections
This will cause torsion in the bracket about the axis that is perpendicular to the runway beam and column.
For bridge crane design, you also have longitudinal forces and these will cause lateral bending in the bracket at the same time. This will cause torsion in the column.
A lot going on here with moving loads, etc. The connection looks hell-for-stout but with a crane upgrade beyond its original intent you have to check it.
Also - with all those welds, and an "old" bracket, you might have a possibility of fatigue issues present - have you had the plates and welds inspected for cracking?
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RE: Torsion on Steel Connections
It's an interesting thing to think about that the connection can offer some moment resistance, but how much cannot be readily determined. Unless there is a method I'm notaware of, which is very possible. If there is I would love to read some material on the topic
Surely it will be conservative if I assume a fully fixed connection and calculate the bracket welds based on the full torsion present. It seems that my FBD should be sufficient without drawing the whole structure, because the only thing that attaches to these brackets are the runway beams. Correct me if I'm wrong in this thinking.
RE: Torsion on Steel Connections
I think you are correct that an exact solution would take time in that the torsional stiffness of the bracket gets weird when you torque it by only a portion of its section ( ie the top flange).
And that torque load application suggests also that cracks may form in the web just below the seat plate.
One load application a month isn’t much but that frequency may have been quite different back in the 1960’s.
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RE: Torsion on Steel Connections
If that is the case, I misunderstood what you said: I thought you were asking about torsion developed from a lateral load (applied to the top flange of the runway beam & perpendicular to the strong axis of the runway beam).
But to answer your question (under the assumption that is what you are after): in calculations I've typically seen that treated like a simple support. However, there will be some fixity so you may want to check it out. What I would do is figure the rotational stiffness of that support (taking into account the stiffness of the bracket, flange of the bracket where the bolts connect [maybe the weakest link], etc), and use that fixity in your model of the runway support girder.
Chances are you aren't going to get much restraint (and ergo, little torque transferred to the bracket from those forces).
RE: Torsion on Steel Connections
There is a lot of stuff out there (i.e. AISC Journal articles, AISC Design Guide 8, etc) that deal with PR type connections. (Although my money is on this thing behaving closer to a simple connection than anything else. A lot of people don't realize that your average simple shear connection has some degree of fixity as well.)
I've dealt with similar situations before myself......not just with brackets but (for example) running a beam over the top of another. I dealt with it as I outlined it my post above.
RE: Torsion on Steel Connections
The problem is this isn't truly a stiffened seat connection due to the web and flanges of the beam being welded to the column. Could I justify reducing the eccentricity to the middle of the w18 instead of using 26 in and assuming load is transferred to the plate as a uniformly distributed load?