fredPE
Structural
- Apr 10, 2007
- 25
I have been doing some plan reviews, where I get to see how different companies do their PT designs. I am relatively new at designing elevated slabs, so I was curious as to the overall design philosophy that I see in the projects that cross my desk, and how that relates to people on this board.
It seems that a lot of companies are really post-tensioning their slabs with 100% and some up to 150% of the DL being balanced. The stresses all work out, but when the design live load is simple residential loading, the section is in compression along the entire length at the full load. This would seem to make sense if you could do that and cut out all the bottom rebar from the slab (as allowed if you are under the 2*sq.rt. f'c limit), but in these designs, they still put in quite a bit of bottom steel.
Basically, I was just wondering if there is a certain design philosophy of balancing all of the dead load in order to get better behavior out of the slab? It is my understanding that it is most economical to just make your stresses work for the load you are designing to.
It seems that a lot of companies are really post-tensioning their slabs with 100% and some up to 150% of the DL being balanced. The stresses all work out, but when the design live load is simple residential loading, the section is in compression along the entire length at the full load. This would seem to make sense if you could do that and cut out all the bottom rebar from the slab (as allowed if you are under the 2*sq.rt. f'c limit), but in these designs, they still put in quite a bit of bottom steel.
Basically, I was just wondering if there is a certain design philosophy of balancing all of the dead load in order to get better behavior out of the slab? It is my understanding that it is most economical to just make your stresses work for the load you are designing to.
