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RE: Concrete Cover Over WF Beam

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Either way, it seems pretty problematic. If you leave the thin concrete cover, it’s going to crack up, as several others have pointed out. Putting an exposed steel cover plate would create problems, as well – what happens when your beam isn’t perfectly flat (or, at least, not flat enough for floor tolerances)? Suppose it has a little excessive natural camber? It seems like control of the floor flatness will be a challenge.

 

Can you consider other alternatives? The girder-slab system that Matthew Stuart suggested could be a possibility. Or maybe just a thicker topping slab?

 

Sorry, not a lot of help – just a few thoughts.

 

-- Joel

 

 

Joel Adair, PE, LEED® AP

Structural Engineer  
SHWGROUP

 

 

 

From: William Haynes [mailto:gtg740p(--nospam--at)gmail.com]
Sent: Friday, August 21, 2009 12:39 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Cover Over WF Beam

 

It is going to be sealed concrete, no other finish.

I was thinking I could put a 3/8" cover plate along the entire length of the top flange of the beam and just pour the concrete up to each side of the cover plate . The top of the cover plate would then be exposed when looking from the floor level, which is alright for this application. But, there will be a shrinkage crack that will form on each side of the cover plate that would need to be closed with joint filler.

Any other ideas?

WH

On Fri, Aug 21, 2009 at 11:11 AM, David Topete <d.topete73(--nospam--at)gmail.com> wrote:

Expect the 3/8" concrete to spall/crack/crumble.  No way around that.  What's gonna be the finish flooring material?  I'd say leave that strip bare during the placement of the topping, and come back with a non-shrink grout to fill above the WF.  But, others may have a better/simpler idea...

 

On Fri, Aug 21, 2009 at 6:49 AM, Bill Polhemus <bill(--nospam--at)polhemus.cc> wrote:

William Haynes wrote:

I have a case that is very similar to the following detail. I am only going to have 3/8" of concrete cover over the top of the WF beam.

Does any preparation to the beam typically done (sandblasting, applying epoxy) in order to insure the bond of the concrete to the top flange of the beam? This cover is not structural, is there a minimum cover recommended?

http://www.kerkstra.com/Hollowcore%20Details%2012%20-%2007/2312-1.pdf


Will Haynes

Remember that "cover" is specifically for protection of steel reinforcement against the elements. Unless you are going to add shear transfer studs (e.g.) to the top of the beam, you cannot expect a predictable amount of "bond" between the concrete and the steel so it doesn't matter if you "prepare" the surface or not. I'm not aware of anything other than studs, angles, etc., welded to the top flange of the beam that would provide a predictable shear transfer.

So the short answer is "whatever is practical." Make sure you don't have a situation where cracks due to incompatible displacements result; otherwise, I don't know that there are any rules about cover.

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