Ductility Analysis of Prestressed Concrete Members with High-Strength Strands and Code Implications

This paper presents the effect of high-strength strands on the design of prestressed concrete (PSC) members; in particular, the tension-controlled and compression-controlled strain limits that are provided in the current ACI 318 code are discussed. The modification of the strain limits is based on a ductility analysis for which various ductility and deformability models were used so that the characteristics of the high-strength strands and the effect of the prestressing force could be considered. The ductility and deformability values were obtained from the moment-curvature relationships and the load-displacement relationships of the simply supported PSC beams. The material model of the Grade 1860 (270 ksi) strand was modified to represent the actual stress-strain behaviors of the high-strength strands. The effects of several design parameters such as cross-section type, compressive strength of the concrete, tensile strength and area of the strand, and level of the prestressing force are presented in detail.