Kinked Flat Slabs

[slickdeals]

Folks,
I am looking at the design of a slab that is flat over half the bay width and starts sloping down at a 25 degree angle. The flat slab is supported on a square grid of 8.5m x 8.5m.

Has anyone dealt with such a situation in the past and if so, what are the things to watch out for?

The slab will be post-tensioned in one direction (perpendicular to the direction of the kink). In the other direction, I was planning to design as a mild-reinforced slab.

At the kink, I was planning on extending the bottom bars from each side to the top (similar to stair landing/run detail) with proper extension beyond the kink.

Thoughts/suggestions for detailing are appreciated.

 

[Teguci]

Consider diaphragm action. The tension side of the diaphragm will want to straighten the kink and the compression side will want to fold the kink. The slab will need to resist this moment.

As for experience, no. Most garage ramps (my experience) are detailed to occur at beam locations.

If you go through the expense of a PT deck, why wouldn't you do it in both directions?

That being said, if you do PT the other way, you will need a beam at the kink (or a thick enough slab to resist the moment).

 

[slickdeals]

I don't want to PT the other direction as it will be impossible to detail post-tensioning tendons through this kink, unless others have ideas that I don't.

 

[dik]

Treat it as a normal slab and crank the reinforcing to match the slope, cutting the rebar as needed and extending it to the 'far side'. Don't have tension rfg at the 'bend' so that it will 'pop' the concrete off if in tension. In the opposite direction, the kink may provide added stiffness that should be considered.

Dik

 

[rapt]

Teguci,

Re your last comment about a moment from PT at the kink, as long as the tendon kinks at the same location (it will be a curve, not a sudden kink) by the same angle change, there is no moment induced by the PT. The biggest problem with PT will be the transition through the kink and any tendency the pop out the concrete in the curve of the tendon through the kink.

But you cannot hand a sudden 25 degree kink in a carpark slab, there has to be a transition or cars will bottom out as they go across it!

Slickdeals, otherwise, as RC do as you have suggested and all should be ok. Make siure there is top and bottom reinforcement through the kink like a stair detail as you suggest.