Wall Support in Basement
Wall Support in Basement
(OP)
I wanted to get an opinion on something. Say you have a basement with two posts supporting the main girder (W8). There is a wall oriented perpindicular to the girder that is currently not supporting it and is approximately 3.5' from one of the posts. Do you see any potential issues with the basement slab if the wall were made to be a load-bearing wall and the post closest to it was removed? Obviously any necessary reinforcemtne to the beam would be required, but I am asking more about any potential issues with the wall.
I am rationalizing it this way: it is an approximately 7.5' high wall. Even assuming a 4 kip reaction, this would provide a load to the SOG of about 400plf over the length of the 10' long wall. Does this seem like it could be a problem, possibly causing cracking of the slab?
I am rationalizing it this way: it is an approximately 7.5' high wall. Even assuming a 4 kip reaction, this would provide a load to the SOG of about 400plf over the length of the 10' long wall. Does this seem like it could be a problem, possibly causing cracking of the slab?






RE: Wall Support in Basement
A old nomograph I have says 400 plf is right on the edge for a 4", non-reinforced slab with f'c = 3,000 concrete and a modulus of subgrade reaction (k) of 100 pci.
If the wall weight is in addition to the reaction load, you may be over.
But greater concrete strength or great k will increase the capacity.
RE: Wall Support in Basement
RE: Wall Support in Basement
What is the wall that is 3.5' from the post constructed of?
If it is 8" concrete/masonry, you probably have a footing under it. In residential construction you have to be careful what you assume when going from non-bearing to bearing.
If it is wood frame, you cannot assume anything.
A basement slab is not intended to carry any structural loads. If you have a typical slab on grade in a residence, it is really not a slab on grade. In most parts of the country, the basement slab is about 3.5" thick and is cast on the footing supporting the foundation wall. The slab thickness can vary dratically and there was probably no control over the compaction or thickness, so you cannot assume any slab support from the soil.
Basement slabs frequently have as little as 2" thickness covering a settlemet void and the collection of construction scraps (wood, drywall, loose soil).
This will take some on-site investigation.
RE: Wall Support in Basement
The idea that the basement slab could be 2" definitely scares me. Maybe I'll steer clear of that!
Why in the world would you build a nice, huge basement with the only obstruction being a couple of posts? Why not just size the girder to take the loads and make it a much better basement? Seems like common sense to me - would it really add that much cost to the house to do it at the beginning?
RE: Wall Support in Basement
RE: Wall Support in Basement
If your wall is wood, runs parallel to your floor joists, and appears to bear directly on the slab, I'm willing to bet that wall was never intended to be bearing. As such, there probably isn't a thickened slab below it nor a slab designed to recieve a line load from the wall.
RE: Wall Support in Basement
RE: Wall Support in Basement
Never, but never question engineer's judgement
RE: Wall Support in Basement
The load from the W8 will not span out over the length of the wall as you suggest. It will concentrate at the post.
Mike McCann
McCann Engineering
RE: Wall Support in Basement
RE: Wall Support in Basement
Mike McCann
McCann Engineering
RE: Wall Support in Basement
RE: Wall Support in Basement
Mike McCann
McCann Engineering