Quote:
Originally Posted by ton80
Originally Posted by ltcdfancher View Post
Why would a cast concrete wall require a separate lintel? The concrete is a monolithic structure above the window and around it to the bearing surface at the slab. Depending on the orientation of the embedded steel in the wall, it ‘should’ even be possible to add a double slider in place of a single-hung window. Penetrating radar above and around the window to document steel placement would be prudent, I think. Then, of course, a nod from an engineer, the ARC, AND the building department. From there, grab the wall saw!
Brian L99 is correct. Concrete walls are not monolithic structures. Built of concrete only, they would fail if there were any openings or any movement of foundation or shrinkage as the concrete cures. They require reinforcing steel since concrete has very little tensile strength. Concrete slabs have cuts made so that the inevitable shrinkage cracks that occur during curing are controlled and not unsightly.
Concrete walls will have reinforcing steel placed in the wall at the appropriate locations to provide the tensile strength to carry the loads around the designed openings. Cutting an opening for a double slider will be much larger than any reinforcing placed to span a single window. I do not see how any structural engineer will approve any design to create an opening larger than the original single window without extensive external steel reinforcing.
|
Unfortunately, that theory (expansion cuts) works about 30% of the time. Maybe 50%-60%, if you cut the mesh before you pour the concrete and make your expansion joint cuts along the wire mesh cut. I've yet to see a large concrete slab, that doesn't have a "crack" or 2, somewhere other than along an expansion cut.
As you point out, Concrete has extremely low tensile strength, but high compressive strength. We occasionally use "structural slabs" which have reasonably good tensile strength (& can be monolithic), but that strength comes from the steel design. The problem with them, is once you have to cut into the slab, you defeat the entire design premise.