Hello everyone,
a question for someone working with concrete structures. By mistake, two reinforcement bars with a 20mm diameter were cut at the top of a doorpost in a house built in 1950. The reinforcement bars were located directly under the concrete in a load-bearing wall. Is this something that needs to be restored, can it lead to cracking if they are missing, or was their main function during the actual casting?
20 mm is really strong, so the wall probably bears significant forces. Concrete is very strong under compressive forces but easily cracks under tensile forces. Therefore, there is a clear risk that the opening will crack if the concrete is subjected to large forces from above down towards the opening. This is prevented by the rebar, which holds the concrete together even in the directions where it is weakest.
Edit: Simple paint drawing to show the tensile forces that the rebar can no longer withstand and where concrete is weak:
I hired a welder who welded rebar end to end and filled with cement to cover the bars. The welder is involved in construction welding but didn't really think it made much of a difference with the two bars; I didn't want to take any risks though. Just wanted to check with others involved in construction if it sounded reasonable.
20 mm is really substantial, so the wall is probably bearing large forces. Concrete is very strong under compressive forces but cracks easily under tension. Thus, there is an obvious risk that the opening will crack if the concrete is subjected to large forces from above down towards the opening. The rebar prevents this and holds the concrete together even in the directions where it is weakest.
Edit: Simple paint drawing to show the tensile forces that the rebar can no longer resist and where concrete is weak.
I brought in a construction welder who welded two rebar end to end and applied cement and covered the bars. However, there must be more rebar at regular intervals to hold the concrete together. As I understand it, construction is usually greatly over-engineered, shouldn't the force be distributed to other rebar?
Hello,
20 mm rebar is generally very coarse for a door frame, so it's likely that these bars are related to something else. It's hard to say what they might be for without seeing the surrounding area, but an example is as shown below. If there is a large concentrated load coming from above from a pillar, more reinforcement is needed above the door.
Regardless, the bars are now welded together, so the load-bearing capacity is restored, and no further action is required.
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MultiMan said:
