Flexural Strength of Reinforced and Prestressed Concrete T-Beams

Abstract

This article examines the behavior of T-beams at nominal flexure strength. The authors begin by explaining the fundamental theory, then equations are derived for the various calculation methods used in the study. Explanations are provided for the differences between the various methods, with special emphasis on the difference between the LRFD (the AASHTO LRFD Bridge Design Specifications) method and the methods of other codes and references. For non-prestressed T-beams, the LRFD and STD (AASHTO Standard Specifications for Highway Bridges) methods are compared with the results of a strain compatibility analysis using nonlinear concrete compressive stress-strain curves. Prestressed beams are also evaluated. The authors conclude that the equations for calculating the flexural strength of T-beams in the current AASHTO LRFD Specifications are not consistent with the original derivation of the equivalent rectangular concrete compressive stress distribution for flanged sections. For non-prestressed T-beams of uniform strength, the equations given in the AASHTO Standard Specifications provide reasonable estimates of the flexural strength of flanged sections. For prestressed T-beams of uniform strength, a combination of the current AASHTO LRFD and Standard Specifications provides a reasonable approximation of flexural strength. In this case, the steel stress at nominal flexural strength is determined by the methods of LRFD, while the equivalent rectangular concrete compressive stress distribution of STD is used to calculate the depth to the neutral axis and flexural strength.