High-strength self-consolidating concrete girders subjected to elevated compressive fiber stresses, part 1: Prestress loss and camber behavior

Abstract

The design of prestressed concrete members is restricted by the requirement that the extreme compressive fiber stress at midspan of simply supported members be less than 60% of the concrete compressive strength at release of prestressing. The purported purpose of this limit is to address serviceability performance, but it places unnecessary limits on the capability of the materials. For this research program, six prestressed concrete girders were produced with high-strength self-consolidating concrete and subjected to compressive fiber stress levels ranging from 65% to 84% of the concrete compressive strength at release of prestressing. Time-dependent concrete surface strains were measured using a mechanical strain gauge, with a focus on measuring drying creep and determining its relationship to prestress losses. This research demonstrates that current American Association of State Highway and Transportation Officials load and resistance factor design prestress-loss prediction methods developed for high-strength concrete overestimate losses by 18%, whereas older methods for prestress losses developed for normal-strength concrete produced more-accurate results. Based on these results and work performed by others, the authors concur with increasing the allowable compressive stress limit at any location to 70% of the concrete compressive strength at release of prestressing.