cut opening in exist. flat slab elevated floor
cut opening in exist. flat slab elevated floor
(OP)
Owner wants to cut 8' x 8' opening in 10.5" tk exist. flat slab elevated floor. It occurs within intersection of the middle strips. Bays are 25' x 20'. As far as design aids, all I have been able to find are articles that are too general in nature. Yes, I know reinforcing will be required. I need references on how to design the reinforcing.
Thanks for everyones help.
Thanks for everyones help.






RE: cut opening in exist. flat slab elevated floor
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: cut opening in exist. flat slab elevated floor
BA
RE: cut opening in exist. flat slab elevated floor
RE: cut opening in exist. flat slab elevated floor
I will be interested to read how to go about reinforcing the slab, though.
RE: cut opening in exist. flat slab elevated floor
If the slab is post-tensioned, it would be necessary to tie off any tendons coming in contact with the edges and re-stressing.
It would make sense to cut the opening a bit larger than needed and provide a steel channel framing around the periphery and anchored to all four edges.
BA
RE: cut opening in exist. flat slab elevated floor
You have to check the adjacent panels, as continuity will be removed. Need to analyze the remaining part of the slab. Hope you have the drawings.
If it is bonded post-tensioning, restressing would not be an issue, but if unbonded like used in the US, restressing would be required.
RE: cut opening in exist. flat slab elevated floor
The slab is not PT. The area encompassed by the opening will be a clear opening and will not deliver any load to the opening edges. The remaining area outside the opening will not have any unusual loadings.Yes, I do have the drawings.
After reading the replies, it makes sense reinforcing may not be required. Isn't the purpose of the middle strip reinforcing steel to deliver the middle strip load to the column strips? Thus, if there is no load (since there is no slab due to 8' x 8' opening), then there is no loading to deliver to the column strip?
BA - Was your comment "It would make sense to cut the opening a bit larger than needed and provide a steel channel framing around the periphery and anchored to all four edges" only applicable if the slab was PT (which it is not)? If you didn't just mean it for PT, then what would the design of the reinforcing be based on?
RE: cut opening in exist. flat slab elevated floor
If in your reach, providing an edge member (that completely replacing structurally the voided part was the -if soundly made- conservative old practice) may help to ensure you have better behaviour there, but now without such complete overtaking of the lost slab by the edge member, just what revealed it is needed.
RE: cut opening in exist. flat slab elevated floor
If there had been a load placed around the periphery of the opening, the channel would be designed to carry that load over a span of eight feet. As there is no such load, channels are redundant.
However, I would be concerned about overcutting at the corners of the opening such as you would expect from a circular saw. Overcutting should be avoided.
BA