Longitudindal Construction Joint in a beam

[ataman]

Hi

I have a detail where a concrete beam supports a slab on either side. On one side, the slab sits on top the beam (conventional) and on the other side site at the bottom of the beam (like an upstand beam).

The difference is slab levels is about 18" so I don't think that the contractor can do this in one pour. Any comments here???

If he can't do this in one pour then it is likely that I will have a longitudinal construction joint along the length of the beam. I would like to use the deepest beam section since the span is about 22 feet. I was thinking of calculating the shear flow and making sure the stirrups can transfer the load across the construction joint.

Is this a reasonable procedure and are there other things that i am missing?

Any comments are welcomed.

Thanks

 

[lkjh345]

ataman:

Are you proposing your joint to be horizontal or vertical?

IMHO: I would cast the bottom of the beam with the lower slab, and have a horizontal joint along the length of the beam, then cast the upper portion of the beam with the upper slab. This, in concept, would be similiar to a filigree beam/slab system.

I would have the contractor rough the interface surface of the lower portion of the beam so that you can take advantage of shear friction between the two pieces to transfer the horizontal shear in the beam.

 

[civilperson]

The crack to worry about is the possible vertical crack at the face of the beam and the edge of the slab. The designed stirrups will suffice for the shear across the horizontal construction joint as you mentioned.

 

[ataman]

Thanks,

Civil Person....are you concerned because the stirrups are acting as anchors in tension supporting the bottom slab....the stirrups will only have 1 1/2 inch cover from the edge of the beam and I suppose can cause cracking