The reinforced concrete beam (approximate dimensions 36" x 18") shown in the image below has a row of circular holes at 3/5ths of the height of the cross-section at approximately 300 mm centres.

My question is why does this concrete beam have these holes?

My first thought is that these holes were due to the tie bars providing lateral support to the formwork vertical walls. However, they appear to be too frequent for that to be true.

row of circular holes through concrete beam

  • $\begingroup$ Where is this beam? Is it a parking structure or something of the sort? Such large holes seem more appropriate for passing any pipes which may become necessary. $\endgroup$
    – Wasabi
    Commented Apr 7, 2020 at 17:34

1 Answer 1


I've not seen them before but I think that they are surely penetrations to run wiring. They on top for reasons including

  1. close to the lid where wiring would be normally attached between the beams
  2. in a place of lower bending stress, near the compression zone, not in the tension zone were reinforcing would be located or concentrated

I suppose that they could be for air flow, a venting of sorts.

In any case, I believe that they are not there as a design feature of the beam. That is, these holes serve no purpose for the beam itself.


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