SAICE-Design Of Prestressed Concrete Flat Slabs

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Reports 17 and 25 require a minimum prestress level of 0.7MPa. The CEB-FIP code requires 1.0MPA and the ACI 0.86MPa.In a lecture given some years ago it was suggested that less than 1.4 MPa was too low a prestress,1.4 to 3.5 MPa was the'proper'range,and over 3.5 MPa would cause excessive shortening. Many slabs are now designed with stresses less than 0.7 MPa.
It is the Committee's philosophy that there is a continuous spectrum of concrete from plain reinforced to fully prestressed concrete,and that there should be no arbitrary limits on prestress levels.
It is considered that prestressed flat slabs are essentially ordinary flat slabs,subjected to additional lateral loads from tendons,which reduce the effective load on the slab,and to longitudinal prestress which helps to reduce cracking.