Holes in concrete beams
Holes in concrete beams
(OP)
I need to place an 18"Wx10"D hole in a 12"Wx24"D concrete beam. Of course, I am placing it where I have the least shear (about midspan of beam) and based on the tension reinforcing in the beam (3#7 bottom) I calculated "a" from
a = AsFy/0.85(f'c)(b)
My question is: As long as my calculated "a" is smaller than the actual "a" in the field, I should be okay. Is this correct? In this case, my calculated "a" was 3.53 inches. I placed the hole in the beam such that I have 8-inches of concrete on the top, 10-inches for the hole depth and 6" of concrete below the hole providing encasement to the beam's bottom reinforcing. It would seem to me that since the compressive stress is satisfied it should be okay to place the proposed hole as described. Am i missing anything?
Thanks for any assistance.
a = AsFy/0.85(f'c)(b)
My question is: As long as my calculated "a" is smaller than the actual "a" in the field, I should be okay. Is this correct? In this case, my calculated "a" was 3.53 inches. I placed the hole in the beam such that I have 8-inches of concrete on the top, 10-inches for the hole depth and 6" of concrete below the hole providing encasement to the beam's bottom reinforcing. It would seem to me that since the compressive stress is satisfied it should be okay to place the proposed hole as described. Am i missing anything?
Thanks for any assistance.






RE: Holes in concrete beams
It is not just the principal moment that you are designing for. It is possible that the beam could be half loaded. This shear developed by the half loading can also add a secondary moment with the shear lag caused by the opening that you have not taken into account.
Additionally, you may need additional stirrups in the upper and lower segments. The shear thru each segment needs to be designed for.
It is probably a good idea to also check deflections.
I would ask your supervisor for some help on this one!
RE: Holes in concrete beams
A couple of things to consider:
- If the hole is large wrt to the beam depth, then you may get a Vierendeel-like moments at the corners of the opening.
- Suggest you have filleted, rather than sharp, corners.
RE: Holes in concrete beams
Any other thoughts? Anyone has literature on this subject?
Thanks for the info.
RE: Holes in concrete beams
book on openings
RE: Holes in concrete beams
In an office building, the Owner could elect to locate his furniture on one side of the beam and put a hallway on the other side. In a storage building, half could be loaded and the other half unloaded.
RE: Holes in concrete beams
RE: Holes in concrete beams
Dario Gonzalez, P.E.