Design of Prestressed Flexural Sections by the Unified Design Approach

Abstract

The Unified Design Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members was incorporated as Appendix B of ACl 318-95. The provisions are intended to unify the strength design of reinforced and prestressed concrete sections based on their ultimate behavior limit states. The new provisions affect the maximum reinforcement limits for flexural members, strength reduction factor O and moment redistribution. This paper presents a procedure for the design of prestressed flexural sections by the Unified Design Approach. Design examples are given to illustrate the design procedure. The new procedure defines a transition behavior region in which the strength reduction factor O, to be used for strength computation, varies linearly with the strain in the extreme tension steel. The design of sections falling in this behavior region involves an iterative procedure. Some design aids are given to facilitate design in this transition region.