Some concrete elevator core door openings have lintel steel, some have just the default wall steel
In the past three years as a heavy commercial concrete foreman I have seen several designs for concrete stairwell and elevator shaft door openings. Some have no added lintel steel at all, just the default wall steel, such as #5s 12″o/c each way double mat for a 12″ wall; others have very elaborate lintel steel which resembles a grade beam; others have a special lintel cage with stirrups, but I have seen cases where the stirrups were spaced further apart than the default wall steel, with smaller horizontal bars than the default. In one particular case the “lintel” steel seemed inferior to the default wall steel. In all cases, the header only needed to support standard metal decking; no extreme circumstances. It makes me wonder why there is such a disparity of ideas for similar applications. I have also seen this with foundation walls, with some walls carrying heavy stonework for several stories receiving very minimal vertical rebar support, #5s @ 4 feet on center. Why such a mix?
Alot of that lies with the structural engineer. Each one has their own way of deeming something as safe. It also may be that the lintel steel has been produced for lighter grade work. As far as the rebar support, #5s @ 4 feet on center, it does not take much rebar to make concrete twice as durable as it was on its own without the rebar.
If the lintel steel has indeed been made for lighter duty, it will require greater reinforcement, hence the cage with stirrups.
The decision also comes down to cost, what is he cheapest, most effective way to make it stand up?? Rebar is cheap and it greatly increases the strength of the concrete. But the main reason there is such a mix lies with the Structural Engineer; their choice is partly directed by the structure around it, the extent of the modifications to be done, and how it will affect the structural integrity.
Hope that helps.
