Post Tension Slab on Ground of varying thickness

[Dunstan]

Dunstan
A contractor asked me to design a hanger Post Tension slab for a plane hanger of dimension 29.2m(approx.95.8ft)x 32.4m(approx. 106.3ft). I proposed a 150mm (6") thick slab with twin 1/2" mono-strands 270k at 0.85m (33.5") c/c, both ways.
I now have a request to allow for two drains with appropriate drainage slope on the slab.
The high point is at mid slab (of the 29.2m dimension, which gives the slab a thickness at that point of 225mm (9"), falling to the nearest low point 6.4m (21ft) away to the original slab thickness of 150mm (6"), then back up to a high point 8.2m (26.9ft). See attach sketch.

My question, can I still pull my strands at my original slab thickness mid point of approx. 75mm (3"), or do I need to follow the profile of the slab thickness center line as it varies up and down?

 

[KootK]

- I believe that you would need to follow the profile of the slab up and down if you want to avoid the PT imposing moment on your slab.

- Keeping the PT in its original position would, no doubt, be easier to build. And I'd think that you could do this if you're willing to deal with the moments mentioned in #1.

 

[Dunstan]

Dunstan
TO Kootk

Thanks for your reply; deep down I was hoping I would not have to do what you said, just to get away from the additional difficulty.