Bottom Flange Confinement Reinforcement in Precast Prestressed Concrete Bridge Girders

Abstract

The AASHTO standard bridge specifications require that nominal reinforcement should be placed to enclose prestressing steel at girder ends for at least a distance equal to the girder’s height. The AASHTO LRFD bridge specifications state that the minimum requirements for this confinement reinforcement is No. 10 (#3) bars at a maximum spacing of 150 mm (6 in.) for at least 1.5 times the girder’s height. Neither standard nor LRFD specifications justify the need for such reinforcement. The main objective of this study is to investigate the effect of confinement reinforcement on the performance of prestressed concrete bridge girders. Of particular interest is the effect on transfer and development length of prestressing steel and on the shear capacity of prestressed girders. The experimental investigation includes testing the flexural and shear capacities of 610 mm (24 in.) deep T-girders and 1,100 mm (43.3 in.) I-girders. The results indicate that (1) neither the amount or distribution of confinement reinforcement has a significant effect on the transfer length of prestress strands; (2) at the AASHTO calculated development length, the amount of confinement reinforcement does not have significant impact on either the nominal flexural capacity of bridge girders or bond capacity of the prestressing steel, however, the distribution of confinement reinforcement along the entire length of the girder results in improved ductility and reduced cracking under extreme loading conditions; and (3) confinement reinforcement improves the anchorage of strands at girder ends, and consequently, the shear capacity of prestressed girders.