Eccentricity of Shear Connection

[J1D]

At perpendicular beam-to-beam connections, it seems popular nowadays to use a shear plate extruding out from flanges. This means the secondary beam will transfer not only shear, but a torsion to the primary beam. I wonder how this is considered in your analysis. What about the situation that the primary beam is connected to column with shear plate as well (not torsional restrained)?

Thank for input in advance.

 

[WillisV]

This is typically not considered in the analysis of the support girder because the eccentricity is taken out in the bolt group itself (e.g. the bolt group is designed for both the shear and the eccentric moment). See AISC 3rd Ed p10-160 for a discussion on this.

"...the bolt group should be designed to resist both the shear Ru and the eccentric moment Rue. The beam end reaction will then be carried through to the center of the supporting girder web."

 

[DaveAtkins]

I went to a seminar many years ago, where the presenter showed that the small amount of rotation in the supporting girder causes a tiny, tiny amount of torsion in the girder. By relative stiffness, the moment goes into the bolt group, as WillisV mentioned.

DaveAtkins

 

[J1D]

Thanks. Unfortunately, I don't have AISC 3rd Ed manual handy and couldn't get the page (I have the old one for 1993 spec). WillisV, can you show a bit more info?

I can understand that if there is a bolt group and installed to take some bending moment the M diagram of the secondary beam is pretty close to that of a simply supported beam. But what about the shear tab has only two bolts (and with horizontal slots)? In computer analysis do you model the connections at extended shear tabs with 2 bolts as a pin or rigid?

 

[WillisV]

If the tabs are designed correctly to take out the moment due to the eccentricity then you design the beams as pinned just like every other simple shear connection. If you are worried about the slots just use slip crit bolts.

 

[DaveAtkins]

Don't worry about the slots. Unless you are using A307 bolts (which I don't recommend!), there will be enough initial pretension to prevent slip.

DaveAtkins