Post Tensioning Edge Curl

[LarryStruct]

We are currently designing a three story office building and the architect wants to use a one way bonded post tensioning floor slab system. The edge of the 9" slab bears on reinforced masonry walls. This is our first post tension design and I have been told by other engineers that there is a possiblity of edge curling in the slab and that we should drop the slab at the bearing wall to create a horizontal beam. The post tensioning contractor indicates that this is not necessary and is expensive to form.
Has anyone had an edge curl of the slabs after tensioning the strands?

 

[Ingenuity]

I have designed and constructed many PT slabs and have not experienced edge curling in suspended slabs.

SOG's can experience edge curling but this is related to the retention of water in the bottom of the SOG and hence differential curing and possible shrinkage cracking - it is not particularly related to PT or RC construction.

I would agree that the downturn edge "beam" will be expensive to form.

In your case (with perimeter walls) i would be concerned about the correct detailing of the walls and the slabs - and to minimize the restraint that may be present depending on the location and stiffness that the walls provide, as the slab want to shorten due to elastic, creep, shrinkage and thermal actions.


HTH

 

[RiBeneke]

The only reason that I can think would cause the slab edges to curl would be if the tendon anchorages at the perimeter of the slab were at a high level within the depth of the slab. The bending moments at the slab edges are close to zero and the tendons should then be near the mid-depth of the slab at the edges.

I agree with Ingenuity's comments.

 

[rockstar]

You may want to look at "separating" the wall from the slab. I have developed a detail that uses a 6x6 ms cont. angle bolted to slab edge, and which support the outer skin of the masonry wall. This allows you to manage any curling or other concrete deforamtion without having to worry about tolerances and junction details