Double Angle Connection with Torsion
Double Angle Connection with Torsion
(OP)
The EOR has requested that I provide a calculation showing the torsional capacity of a bolted-bolted double angle connection between a W8 beam and a W8 girder. My thought was to resolve the torsion through bolt tension in the bolts on the beam side. My concern now is how I design the angle leg for this torsion. Should I check the angle leg for torsional stresses in addition to the weak axis flexure induced by the bolt force from the torsion OR should I ignore the the torsional stress in the angle leg and design the angle leg for the weak axis flexure only? It would seem that the angle thickness would have to be pretty thick to resist any type of torsional forces. Any input would be greatly appreciated.
Thanks,
Val
Thanks,
Val






RE: Double Angle Connection with Torsion
BA
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
BA
RE: Double Angle Connection with Torsion
The only way you can resist a substantial amount of torsion, even if the beam is capable of taking it, is to connect the flanges to create a push-pull couple.
RE: Double Angle Connection with Torsion
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Double Angle Connection with Torsion
Yes, I should have seen that last night. The beam flanges would have to be coped to clear the girder flanges, so the only part of the beam available to carry torsion is a six inch height of the web.
For any substantial torsion, the beam flanges would have to be connected to the girder flanges. And then the double angles would be carrying only vertical shear.
BA
RE: Double Angle Connection with Torsion
I've seen jobs where the detailer is required to provide connections like half the maximum UDL, or the full shear capacity of the beam, etc....
If the web is the EOR's responsibility, just use angles that are the next size thicker than the web, with long outstanding legs if two bolt rows are needed. Forget the bolts to the beam web and rely on bearing of the beam web on the angles for the torsion. The angles will then be stronger than the beam.
If the web is your responsibility, you may be into web reinforcing as part of your work.
I have had cases like this because of limited headroom, but then I use an end plate on the beam, connected to a piece of tee that is shop welded to the girder to provide a flush finish.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Double Angle Connection with Torsion
Val
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
I agree, but the standard practice in my area nowadays is for the EOR to require the fabricator to retain an engineer to design all of the connections, to seal them with his engineering seal and to accept responsibility for their adequacy. I have been retained by fabricators to carry out this service on several occasions. I did not agree with the practice, but because I had a working relationship with the fabricator, I complied, albeit unwillingly.
The fees are really not commensurate with the risk and if I were to continue in practice, I would not perform this service any more.
BA
RE: Double Angle Connection with Torsion
Val
RE: Double Angle Connection with Torsion
You must not oblige! It is absolutely wrong for a fabricator's engineer to oblige an EOR who doesn't know what he or she is doing.
Why don't you advise the EOR what you believe should be done in order to resolve the situation. If she is not prepared to accept your solution, then you must demand an instruction in writing as to what detail is to be used. Needless to say, she must accept full responsibility for that instruction.
BA
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
The problem arises when the fabricator has their own special connections that they insist on doing and then the EOR has to redesign to suit.
Sizing beams is usually monkeys work, making connections work is often the hardest part.
That debate aside, I believe that you will find in one of the best practice guides that the EOR should provide a generic detail of any unusual connections to show their intent.
I had a similar situation and as an EOR I agreed to do the connection design for some of the more complex connections as that was easier than conveying all the requirements.
RE: Double Angle Connection with Torsion
Yes, I generally check the outstanding angle legs as two rectangles each taking 1/2 of the torsion. Keep in mind you can't make the angle legs thicker than 5/8", per AISC, to allow the connection to act as a pinned support.
You will find that you can't get much torsional resistance out of two rectangles.
DaveAtkins
RE: Double Angle Connection with Torsion
I thought we did a fairly good job of discussing Valstone's problem, and he seems happy. Why would you be concerned with a connection acting as pinned when it has to resist torsion?
RE: Double Angle Connection with Torsion
The legs are separated by a distance of t(web) + t(leg), so major axis bending comes into play, one leg bending up, the other down.
If the beam web is adequate to resist the applied torsion, minor axis bending of the angle legs comes into play as well.
But the weak part of the whole connection is going to be the beam web, so the question is definitely academic.
BA
RE: Double Angle Connection with Torsion
But I agree there are other issues which may render the point moot.
DaveAtkins
RE: Double Angle Connection with Torsion
I'm still curious as to why you say that. Why not a rigid support? I don't think we know enough about the rest of the structure to define how a given connection should work.
RE: Double Angle Connection with Torsion
So if you wanted to keep the support pinned, and not connect flanges to flanges, you could still take some torsion while maintaining the flexibility in the double angles which is required by AISC.
DaveAtkins
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
I guess I should assume this was attempted, but not possible.
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
DaveAtkins
RE: Double Angle Connection with Torsion
BA
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
DaveAtkins
RE: Double Angle Connection with Torsion
RE: Double Angle Connection with Torsion
BA