Currently renovating the living room, and the wife wants lamp sockets above each window. (I've talked to an electrician who will come and run the conduit and electricity when I'm also lowering the ceiling.) However, I've encountered a problem when using a hole saw in the lightweight concrete beam above the window where the junction box is to be cast. There's a reinforcing bar 2 cm in precisely in the middle of each window. See picture. The question is whether it's okay to cut it off? Is it safe, or will the house collapse? It feels like there should be more reinforcing bars. It seems strange that the reinforcing bar is vertical. I think it should lie horizontally in the middle of the beam.
A lightweight concrete beam usually has reinforcement along the edges of the bottom with cross ties connecting them. Several beams also have reinforcement at the top, making them sometimes completely symmetrical and possible to be mounted in any direction as long as they stand upright. Cross ties are usually also present between the bottom and top. From the image, it looks like you've encountered such a cross tie between the bottom and top reinforcement. Unfortunately, I don't have insight into your continued drilling here, and it partially depends on whether reinforced blocks were used in a load-bearing construction or if the reinforcement is just intended to support the window opening.
Check where your roof trusses are; if you have one directly in the middle over the window, you might want to think twice about cutting it. You probably won't notice anything, but there's a risk of settlement, which is hard to assess.
Beams usually have stirrup irons across the longitudinal direction, connected at the corners with longitudinal irons. A lightweight concrete facade typically consists of blocks or planks, i.e., a form of element construction. The beam is likely a load-bearing component over the window. A good principle is to let installations be subordinate to the construction rather than the other way around. However, I don't think the house will collapse if you cut off just that small piece of the reinforcement.
An update for those who encounter the same problem. I don't like threads that just end abruptly. With a not completely unfounded concern, I obviously didn't dare to cut the entire rebar, as I could establish that a roof truss was resting on the window beam. However, I dared to use the dremel to grind away half of the rebar's thickness. I sanded it down with a small sanding disc. Then I chipped out the remaining depth on the side of the bar so that the device box would fit. I had to make a slot on the back of the device box corresponding to the bar's width so it could fit in the hole. Then I secured the box with gypsum natural plaster. Now the lamp socket fits with a few millimeters' margin against the rebar. To make the electrician happy, I taped the rebar with 2 layers of age-resistant seam tape that I had lying around so there wouldn't be visible metal in the device box.
Next time just tell the frugan that it’s not possible.