Steel Beam Over Concrete Column/Wall Connection 5

[BONILL]

I have a situation where I have a steel beam over a concrete column. The attached sketch shows the connection. I am trying to make it a moment connection at the top, however my moments are quite large. I was wondering about the possibility of it not being a moment connection. I would really appreciate any opinions on this.

I also have the case of a cantilever steel beam over a concrete wall. The sketch shows am embed plate in the concrete wall. How adequate would this moment connection be.

Thanks for your help.

 

[slickdeals]

Do you need a moment connection for lateral loads?

You don't need a moment connection over the column, if the beam has sufficient capacity to do it by itself. In essence, the moment at the top of the column will be zero (pinned end).

The same concept will apply to the cantilever beam over the wall. The cantilever moment will be carried by the back span with zero moment on the wall. You will have some small moments due to rotation, but it will relieve itself.

 

[dik]

Can you get A325 'J' bolts? I'd use high strength rod if needed with a heavy hex head nut on the bottom...

You may require a heavier base plate because many smaller beams have a relatively thin flange and you may require stiffeners at/near the face of the column to take the forces from your anchor rods to the column itself. Also have to check for interference with column reinforcing. For the small column you have there can be a great loss in moment resistance if you move the anchor rods an inch or so...

Dik

 

[BONILL]

slickdeals,

So in essence the connection would only be to resist uplift loads?
I would not need to design my bolts in the case of the steel beam over the concrete column for tension resulting from the moment?

 

[slickdeals]

Yes, think of it as a hanger connection in steel. Check for the effect prying when the bolts go through the flange of the beam.

 

[BONILL]

Ok. So basically I would just provide bolts for uplift and assume a pinned connection at the top of the concrete colummn? The idea behind this is that since there is not enough moment resistance provided by the bolts that the moment at the top would relieve itself and result ultimately in a pinned connection?

 

[BAretired]

A moment connection between the concrete column and steel beam is possible but probably not too practical. I agree with slickdeals that it is more practical to provide a hinged joint.

A round bar normal to the beam on top of the baseplate would provide a hinged condition. A square bar is nearly as good. In either case, the beam requires stiffeners above the bar.

BA

 

[a2mfk]

I like BA's idea, similarly, if you could eliminate the plate and weld, then use your embed bolts with leveler nuts, shim and pack high-strength grout underneath, and bolt directly thru your bottom flange. Use two bolts if it works for uplift, and/or space as close to the center as possible. I think this will give something you pretty close to a non-restrained connection, and some flex in your bottom flange would help.

 

[ron9876]

I like to add a second plate over the bearing plate which is centered on the column. This keeps the highest stresses from the edge of the column.

 

[a2mfk]

Ron- your idea is similar to BA's, and on second thought I prefer that to mine. Size the second plate and weld only as big as needed for bearing and uplift, centered as you said to avoid stressing and cracking the edges of the column. There should be plenty of flex in that connection to also keep it fairly unrestrained so you can model it as pinned.

 

[JAE]

We've also used elastomeric pads under steel beams - the pad allows a bit of rotation and relieves the stress in the bolts.

 

[BONILL]

Those are very helpful posts.

I went ahead and only used the bolts needed for uplift, and placed them more towards the center of the column. I assumed a pinned condition for design.

Please see attached sketch for another situation. I have a cantilever steel beam supported on a concrete wall, with no backspan. I am thinking of bolting a column to the side of the concrete wall as shown. I would really appreciate your comments. Thanks again.

 

[BAretired]

I would be concerned about the strength and stiffness of the wall itself.

BA

 

[slickdeals]

Agree with BA.
You could also use saddle plates instead of the column. You will have a plate on the front and back of the wall (each sized to take the force due to moment / wall thickness). You can then use the same threaded rod concept.

 

[JAE]

Don't use A325 bolts into concrete. Those are high strength bolts for steel-to-steel connections.

 

[BONILL]

I don't quite follow the saddle plate in front and back of the wall concept.

 

[a2mfk]

BONILL- If I follow the other guys correctly, treat the concrete wall like a steel WF column in a moment frame. Using plates to sandwich the wall, extend up to the beam to develop the T/C moment forces from the beam into the plates. The plates will transfer the forces into the wall via shear through the bolts.

Along with BA's concern, is this wall already built? Maybe you can provide a thickened section of wall (pilaster) in that area, or what about a steel column, where the wall is cast around it?

 

[BONILL]

I went ahead and used a beam with backspan. That way there is no need for concern for the stresses in the wall. Thanks all for your posts.