Checking Cast-In U-Bar for Moment - Will it rip out?

[structuree]

Hi All,

My company commonly uses a similar detail to the below when connecting a steel member to a concrete beam, slab or wall. A 16mm U-bar with 12mm lacer bars to each corner are cast in to the concrete element and welded to a plate. The steel member is then welded to this plate.

How can I check that the U-bar will not rip out of the slab if there is a large moment applied at the steel beam? I feel like a check of 2 x anchors distance 'B' apart would be overly conservative as the U-bar is continuous and you also have continuous lacer bars to provide an extra layer of defence against pullout. My understanding is that the lacer bars would have to fail in shear and/or the portion of concrete would have to rip out with the U-bar for this connection to fail.

The Australian standards don't seem to provide guidance on checking a similar connection. Could anyone shed light on how I should be checking this or point me in the direction of a resource that covers it?

I am also wanting to understand what governs the 'A' and 'B' dimensions specified on the attached markup. My thoughts are that the 'B' dimension would be governed by minimum bend radius & a greater distance apart is better as you'd have a larger lever arm if you're considering each leg of the U-bar resolves the moment in a push-pull manner, and you'd want the 'A' dimension embedded far enough that it won't be too close to the concrete face that it could pull out.

Any advice, thoughts or links to resources would be much appreciated.

 

[WARose]

I'd probably have the "A" dimension be the full development length. (Whatever bar size you need to develop the T/C couple.) I'd lap it with the top & bottom reinforcement. The "B" dimension would be self-evident given that.

The bars would be doing double duty: transferring the T/C couple from the moment.....and also the shear friction transfer of the shear. I can't remember if ACI covers that specifically, but I have typically taken a "set aside" approach. I.e. X amount of area of steel for the Tension/Compression load, and Y amount needed for shear. The total needed= X+Y.

 

[Tomfh]

AS5216 covers it.

https://infostore.saiglobal.com/en-au/standards/as-5216-2018-99009_SAIG_AS_AS_208194/

The logic seems based on ACI318 Appendix D.


If you have a beam or slab to anchor into then you can use long bars, and get a proper lap (which is the point WARose is making above). That way you're not so reliant on cone breakout resistance.

 

[dik]

Do you actually want to transfer moment? If you make the insert plate slightly larger than the HSS section, you can use a fillet weld in lieu of a prepared bevel weld.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[CDLD]

I would check the bar in tension for concrete breakout ignoring any contribution from the lacer bar.
Unless the lacer bar were developed back as per below, I would ignore it.

I am assuming the N16 U-bar is deformed rebar, and so you can check for tension and shear breakout of a hooked bar.
ACI allows the breakout capacity strength of a hooked bar to be equivalent to a headed anchor rod (see below).