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Design of Concrete Encased Beams

Design of Concrete Encased Beams

Design of Concrete Encased Beams

I am about to begin a project on which the owner wants to encase existing steel W shape roof beams in concrete. Does anybody know a good reference for this type of member.  I have a copy of AISC design guide 6 but is seems to be discuss only composite column design.  I have not done any calculations yet but I'm assuming the existing beams can cary the weight of wet concrete, or roof live load, but not both.  Therefore, the concrete encasing the beam will need to act compositely with the beam (shear transfer via welded studs) I've done lots of beams composite with slabs, but never an encased beam.  Any help is greatly appreciated.

RE: Design of Concrete Encased Beams

You can use a plastic stress distribution for this, philosophically the same as for a typical composite beam. The first "gotcha" that I see is that, unlike a typical composite beam, much of your concrete is below the PNA so won't count for anything.

I don't know what type of coating is on the existing beams but I doubt that paint is a good thing. Does DG6 address the required coating, or lack thereof, for composite columns? It seems like the same standard should be applied here.

I think that encased beams are fully composite without shear studs, but check the Manual to make sure. I think it specifically says this. Even so, I'd feel better about it if I added some shear studs. I'd also add corner bars and stirrups at some kind of a wide spacing just for overall integrity.

It's been a while since your original post, so I'd be interested to know how this turns(ed) out.


RE: Design of Concrete Encased Beams

Thanks for the reply DBDavis...the design is out and construction should begin in a month or so.  FYI, I ended up requiring paint removal and included shear studs even though AISC says beam alone will act composite as long as enough cover...also have longitudinal reinforcing as well as stirrups to help w/ durability.

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