Tests of One-Way Post-Tensioned Slabs With Unbonded Tendons

Abstract

T provisions in the ACI Building Code (ACI 318-77)1 for prestressed concrete recognize a difference in the amount of mild steel required for ultimate strength and crack control between bonded and unbonded members. However, the ACI Code equations are based mainly on experience with and tests on beams with relatively low span/depth ratios compared to those common with post-tensioned slabs. Previous research efforts concerning members with unbonded tendons and various span/depth ratios have shown that the ACI• Code expressions for steel stress at ultimate may be unconservative for members such as slabs with span/depth ratios as high as 40 or more, 2' 3 while reinforcement required for crack control may be on the conservative side.