parking garage top slab and sun cambering

[STRCIVIL]

I am investigating what seems to be a crack due to sun cambering at the top levels of a concrete parking structure. During research, I found a guideline by PCI on parking structure desing and it mentioned something about "sun cambering". Can any one explain me where this applies? Does it apply to post-tensioned slabs at the roof level and to the beams and columns? The beams are located at 14'-9" spacing and post-tensioned slabs are 5" thick with 1/2" cable. Cracks are located majorly in the center of the span between the beams. Apparently, there are white residue coming out of the cracks already and some portions have little darker stains.

 

[GoodnPlenty]

I've run into this in a number of structures, usually in hot climates such as Texas, Arizona, etc.

Thermal bowing (Sun Cambering) can be calculated quite easily with some minimal info. The most difficult information to obtain is the temperature differential from the hot surface to the cooler lower surface. With the temperature differential thermal bowing can be calc'd - I thought PCI had some simple eauations ??

The thermal bow can be equated to an equivelent uniform loading that creates the same bowing(deflection).

Use the equivelant uniform loading to determine stresses at the outer faces.
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Could also back calculate thermal differential needed to cause a given bow or deflection.
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This is very common in composite wyth wall panels with a center insulated cavity. With the insulation the thermal differential is maximized and thermal bowing is maximized. This is a controlling item on many composite precast insulated wall panels.

Hope this helps - wish I had the reference here at home for thermal bowing.