Location of connection under combined shear and axial load

[Simran7]

I am designing a connection under combined shear and axial loading on a WF beam framing to WF column. If the center of connection material (shear tab or double angle) needs to be placed vertically offset from the centerline of the WF beam due to some constraints, is there an additional eccentricity that needs to be considered for connection design? Could someone please provide any guidance or refer to an existing post?

 

[karimom]

Yes, you will need to consider the additional eccentricity and weld capacity reduction. I'm not sure where you are in terms of relevant codes. It would be easier to provide guidance if you had a sketch.

 

[rb1957]

so you're mounting your connection on a piece of structure that is not (directly) the WF beam. So how does your shear load (including the couple due to the offset away from this structure) work it's way through this "structure" ? Ultimately the WF beam reacts the shear (in the web) and the torsion (due to the offset).

another day in paradise, or is paradise one day closer ?

 

[Simran7]

Thanks for the response. I have attached a quick sketch showing framing details. I understand there will be an additional moment on bolt group/plate/weld but is there any reference anywhere in the manual or specs or design examples discussion effects of connection location under combined loading. UFM is developed around the principle of eliminating moments but don't know for anything exists on shear tab connections.

 

[rb1957]

not quite as I thought. my 2c …

another day in paradise, or is paradise one day closer ?

 

[JoshPlumSE]

So, there is an eccentricity between the centroid of the applied axial force P (which coincides with the centroid of the beam) and the connection. Therefore, this produces what is hopefully a small moment (P*e) in the connection.

There is also an eccentricity between the shear V (applied at the bolt line) and the face of the column flange. This produces a similar moment (V*h using Rb1957's sketch).

So, yes, there is some additional eccentricity that could / should be considered in the design. There are a number of ways to go about doing this.

There is a book, "Handbook of Structural Steel Connection Design and Details" by Ankar Tamboli. I believe this book suggests that when the axial load is small you should just combine it with the shear load Veq = sqrt (V^2 + P^2) and continue designing it as a pure shear connection. That should be fine when the shear force dominates the behavior. I would think that would be the case for your connection.

 

[KootK]

I think that the moment is in your beam and not in your connection. Or, at least, that's the story I'd be peddling to keep this thing moving expeditiously. It's connection design after all. There's more than one right-ish answer so you might as well pick one that makes life a bit easier for you.

Often times, axial loads in beams really originate at the top flange or higher. So, in reality, you connection may actually be less eccentric for the geometric idiosyncrasy.

 

[rb1957]

I forgot the axial load … e is, of course relevant to the axial load ….

The axial solution is strictly redundant, but there are many simple approximate solutions.


another day in paradise, or is paradise one day closer ?