Design of slabs using the Post tension system, became now a very popular technique in design specially for large span slabs. the main advantage of using PT (Post-Tensioned) in design, is reducing the amount of used steel reinforcement, used in heavy loaded floors as it reduces the thickness of slab by about 20%, This leads to reduce the loads carried by columns and by turn reducing foundation dimensions; especially in high rise building. Recently, investigating the problem of using this type of slab with different opening dimensions and location are limited to a certain aspects.
Frequently, the presence of opening in slab is highly required for passing the different construction services like A.C Lines, electrical cables, pipes of gas & water, etc…. 
In this paper, the effect of openings in PT slabs has been investigated experimentally. An experimental program consisting of six square flat plate specimens, had been carried out. All specimens were made of high strength concrete with target strength fcu= 80 kN/mm² and had a variable opening ratios.