Flexural Behavior of Prestressed Girder with High Strength Concrete

Abstract

The advantages of using high strength concrete (HSC) have led to an increase in the typical span and a reduction of the weight of prestressed girders used for bridges. However, growing demands to utilize HSC require a reassessment of current provisions of the design codes. The objective of one of the research projects, recently initiated and sponsored by the National Cooperative Highway Research Program (NCHRP), NCHRP Project 12-64, conducted at North Carolina State University is to extend the use of the current AASHTO LRFD design specifications to include compressive strength up to 18,000 psi (124 MPa) for reinforced and prestressed concrete members in flexure and compression. This thesis deals with one part of this project. Nine full-size AASHTO girders are examined to investigate the behavior of using different concrete compressive strength and subjected to the flexural loadings. The experimental program includes three different configurations of prestressed girders with and without a deck slab to investigate the behavior for the following cases: 1) the compression zone consists of normal strength concrete (NSC) only; 2) the compression zone consists of HSC only; and 3) the compression zone consists of a combination of two different strengths of concrete. An analytical model is developed to determine the ultimate flexural resistance for prestressed girders with and without normal compressive strength concrete. The research also includes investigation of the transfer length and the prestress losses of HSC prestressed girders. Based on materials testing and extensive data collected from the literature, a new equation is proposed to calculate the elastic modulus for normal and high strength concrete.