Crack Control Bars
Crack Control Bars
(OP)
We are reviewing a project where the owner wants to add additional loads of 10-12 psf on an existing floor. The framing consists of PSI joists and soffit beams.
The joists are designed for a simply supported condition and we have provided #5@12" oc over the soffit beams as crack control bars.
I am calculating a negative moment capacity based on the steel in the slab and am ending up with a moment capacity of the order of 35 k-ft. This in addition to the positive moment of the joists makes up for the total static moment based on the additional loads.
Has anyone done something similar and are there any pointers?
Thanks
The joists are designed for a simply supported condition and we have provided #5@12" oc over the soffit beams as crack control bars.
I am calculating a negative moment capacity based on the steel in the slab and am ending up with a moment capacity of the order of 35 k-ft. This in addition to the positive moment of the joists makes up for the total static moment based on the additional loads.
Has anyone done something similar and are there any pointers?
Thanks






RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
Timeout.....
This is a concrete prestressed joist. It is not an Open Web Joist.
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
When you mention static moment I think about having to check the maximum allowable redistribution of moment by ACI (I think 20%). From what you are saying, all superimposed loads will now be shared between positive and negative reinforcing?
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
RE: Crack Control Bars
It is only compatability torsion if you are not relying on it to reduce moments in other ereas.
RE: Crack Control Bars
You bring up a very important point.
For example, if I have a 30' one way slab on one side and a 20' one way slab on the other, then there will exist an unbalanced negative moment at the beam line. That negative moment will have to be transferred by torsion in the beam into the column.
One of my bosses says that even though these moments may exist, he brought up the question of how this beam would torque considering that it is tied with monolithic slab and into the column.
I could not answer the question. Can anyone point me towards any research in this? Do you design the interior beams for this torsion, which can often exceed the torsional capacity of a non-torsionally-reinforced beam.
Thanks
RE: Crack Control Bars
The moments from both sides will impose a net rotation on the beam. Since concrete beams are not very rotationally stiff it will likely rotate and relieve the torsion. I haven't seen this as a problem.