Composite floor

[enginerding]

I have a steel floor beam at the edge of a stairway that was "field modified" by a steel erector. They wanted me to look at it and design reinforcement if required. That's easy enough.

My question is based on another thing that I saw for the same beam. The steel and concrete floor are designed to be composite (shear studs, etc.). They stopped the pour about 4" back from this edge beam so they could install the stairs. To me, it seems like I will only be able to count on 4" of concrete to act compositely with the steel beam because of where the pour stops. Although I would like to hear other opinions.

Also, where do you normally specify construction joints in a composite floor (alternately, where do you prohibit them)?

 

[PEinVA]

Question #1
If you have enough reinforcement across the cold joint to transfer the shear you need for the edge beam to act compositely. Check out the composite construction in ACI to determine the amount of reinforcing required.

Question #2
On our current job we're specifying about mid span between last beam in the bay. There is only one joint per floor though. We request joint location to review prior to erection/placing of concrete. Any deviation we raise a red flag.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[enginerding]

No reinforcement is present across the cold joint. I would have to dowel, but there is only 4" to develop on this side of the joint. Shear friction requires developing full yield strength of the bars...

 

[PEinVA]

You could hook the bars to develop them. The section in ACI doesn't require shear friction does it? I can't recall and don't have it in front of me.

But some other questions first:

1. Do you really need composite action on this edge beam?

2. How thick is the slab? Could you even dowel effectively?



RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[enginerding]

The beam is fine. A larger size than was required was selected for the design because it was used all over the job. I don't need composite action for this beam at all.

I was just curious how to word specs in the future so that I don't have a problem like this where I really need the composite action. It's a good idea to request a joint plan for submittal.

I could think of reasons (namely the composite beam) where it is good to have mid span joints, but I can also think of reasons (slab effectively cantilevering to midspan) where it would be good to have the joints occur more closely to the beam.

 

[jike]

We usually require construction joints at mid-span of beams and a minimum of 1/2 beff off girder lines. We dowel all joints. We do not allow joints to be placed along lines of studs.

 

[PEinVA]

enginerding,
I assume from your comments the slab is NOT a slab on metal deck, as I was assuming, with my comments.

jike's policy sounds like you can't get in any hot water.

You could also ask for a submittal from the contractor on proposed joint location. Then if something like this happens, it is solely his fault and you can't be made out to be the bad guy.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke