HSS Bearing on Steel Seat Connection (Corbel)

[spieng89]

I have a situation where a temporary column is required and due to contractor constraints a steel corbel or seat connection is required (see attached/below) to support column adjacent to concrete wall. My question is besides checking the anchorage to the concrete wall, weld connection of stiffener to seat/sideplate, is there a localized effect I need to consider on the HSS bearing on the baseplate? In other words even if there is pure axial load, will the HSS want to bend around the stiffener? Also, is there any other effects I may not be considering?

 

[KootK]

Sounds as though you've got a pretty good feel for this.

The bearing plate ought to be designed as a base plate for the HSS so as to prevent the HSS walls from crippling over the stiffener. Alternately, you could make the HSS walls thick enough that they wouldn't cripple even if there were no bearing plate. Lastly, you could have two stiffeners an place one under each HSS wall. That would be structurally ideal but unnecessary in my opinion. Chances are, things wouldn't line up anyhow.

If you haven't already, the stiffener should be checked for combined stresses and buckling.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

I'd check the bolting plate of the bracket to avoid prying on those top bolts.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[Yt.]

perhaps you already consider this, but ....
Maybe need to consider buckling on the seat.
Also there's out of plane moment on the anchorage group because the HSS eccentricity. (HSS center-anchorage reaction line).
Even if it just a temporary column i will try not to consider just axial load, but clearly it's on you criteria and project requirements.

 

[EngineeringEric]

If you can, you may want to bring your 'corbel' top plate over the top of the concrete wall. this will help resolve the moment so you reduce the prying action on the vertical plate. That coupled with a thick enough plate you should be able to use a single stiffener as kootk mentioned, or make the horizontal plate thinner and use two stiffeners under each HSS wall.

I would also see what happens if he outside tip of your corbel deflects say 1/16"... slippage at bolts, deformation per M + V, this may cause a little bit more moment in your HSS... i have no feel for this at all so i would check but that is only because i have no judgement on the effect.

So i assume the wall can handle the moment? and the connections?

 

[BAretired]

It might be prudent to consider the connection hinged at the face of wall, so the column could be designed for a moment of P.e where e is the eccentricity of column from the wall face. In that way, the fasteners are required to carry shear but no moment.

If the column is not capable of carrying P.e then the upper two fasteners should be through bolts with nut and washer on the far face of wall and the wall must be adequate to resist the applied moment.

BA

 

[KootK]

I'm going to have to respectfully disagree with some of that BA. Unless the column is uncommonly stiff and short, the connection to the wall is going to see moment. And since that probably means brittle anchor failure modes, that's concerning. I could get behind the strategy as a belt and suspenders approach if the lower fasteners were designed to take 100% of the shear.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

KootK,

Point taken. To avoid brittle anchor failure modes, perhaps the upper two anchors should be through bolts designed to carry a tension of P(e + t/2)/d where P is column load, e is eccentricity from wall face, t is wall thickness and d is the effective depth of connection.

BA

 

[spieng89]

I have ended up changing the stiffener and side plate to a long (relatively) W-section with baseplate on top where HSS will bear. Placing the anchors in the upper portion of the W-section to reduce tension from moment the anchors will see. Checking rupture, yielding and block shear of flange. The load and eccentricity was too great to get the anchorage and stiffener to work without having a huge "wing" on the side of this wall.

This helped me avoid through bolt anchors as BA mention as an option (couldn't place anchors deep enough to get a sufficient failure cone which led me to investigate through bolts). Plus I don't have a solid understanding of the bearing effects on the bolt i.e. do you consider full length of bolt as bearing on concrete in a through bolt situation? And there would no doubt be some possible spalling at interface between concrete surface and bolt that would induce bending in the bolt.

The ideal situation would be to place column over wall, but that was not an option.

 

[KootK]

I've been down that path before. I recommend welding spacer plates to the top and bottom of the w-beam and installing your bolts through those. That creates a gap between the w-section in the wall that helps s with the prying problem. Also helps with field tolerances.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[wannabeSE]

Has the concrete wall been checked for the eccentric load?