Casting a concrete beam at half.
Casting a concrete beam at half.
(OP)
Hi. At work I'm currently preparing for casting a slab, and the following doubt arised.
One of the beams is a 1m tall beam which starts from the slab and goes up. The slab is a "waffle slab" of 20cm thickness.
The engineer which made the structural design, told us that it is OK to first cast the 20cm of the slab, and the next day we can proceed with casting the other 80cm of the beam.
He sustains this because the beam has continuous stirrups along all the length.
Is this a correct procedure?
Thanks. And sorry if my english isn't the best. I would gladly re-post anything that might not be clear.
One of the beams is a 1m tall beam which starts from the slab and goes up. The slab is a "waffle slab" of 20cm thickness.
The engineer which made the structural design, told us that it is OK to first cast the 20cm of the slab, and the next day we can proceed with casting the other 80cm of the beam.
He sustains this because the beam has continuous stirrups along all the length.
Is this a correct procedure?
Thanks. And sorry if my english isn't the best. I would gladly re-post anything that might not be clear.





RE: Casting a concrete beam at half.
RE: Casting a concrete beam at half.
As long as he has checked longitudinal shear and it is ok, then no problem.
It is very hard to get the formwork right for an upturn beam to be poured at the same time as the slab. The inner face of the form is very hard to brace. Much better to have the day old slab to brace it against.
RE: Casting a concrete beam at half.
I've been trying to find in the ACI Manuals something about this. And have been unable to find it.
I'm trusting the engineer who designed the structure. But my civil engineer side wants to wants to learn more about this.
For example, how many stirrups should you use? Won't the joint of the old concrete with the new one, supossing the area were they join is in compression, tend to fail since the beam is not monolithic?
One other thing I found online was that this procedure shouldn't be done in seismic areas, which kind of makes sense.
But I'm still trying to find some design criteria for when this happens.
Thanks for any info.
RE: Casting a concrete beam at half.
As for the compression issue, your interface is on the tension side of the stress block, or depending on loads and reinforcement, near the neutral axis. I doubt that compression is an issue.
As rapt noted, longitudinal shear (shear flow) must be accommodated.
RE: Casting a concrete beam at half.
RE: Casting a concrete beam at half.
RE: Casting a concrete beam at half.
If you are worried about it then this would be the way to go.