Generalized Flexural Design Equations for Prestressed Concrete

Abstract

S ystematic design equations for prestressed concrete flexural members have been presented previously by Guyon,' Nilson, and Naaman. 4.5 While of significant value, the equation sets presented cannot be applied directly to all steel profiles and loading systems. The set presented by Naaman will define the minimum required beam section moduli, at a given section (normally the point of maximum moment), without consideration of the steel profile, Often, use of these minimum moduli will require a draped strand configuration. Nilson presents essentially the same set of equations, recognizing that a steel profile with varying eccentricity along the span will normally be required. A second set is also presented, which was derived specifically for a constant eccentricity steel profile. The equation sets in Refs. 2 through 5 are thus not directly applicable to design with other common steel profiles such as strands deflected at midspan. The design equations presented here were developed employing the same techniques and principles used previously. However, their development accounts for variables not considered before, and the resulting equation set is directly applicable to the design of general noncomposite prestressed concrete flexural members. The steel profile is considered directly in the application of the equations, and the equations may be used for design with full or partial prestressing. The equation sets may be used for selecting minimum weight standard sections, quickly investigating the effect of different steel profiles on section mod-