Design Model for Confinement Reinforcement in Pretensioned Concrete I-Girders

The 2007 edition of AASHTO LRFD Bridge Design Specifications contains prescriptive requirements for the quantity and placement of confinement reinforcement located in the bottom bulb of pretensioned concrete I-girders. The proposed model canbe used to design confinement reinforcement as an alternative to AASHTO's prescriptive requirements. The model considers a range of I-girder conditions and variations, yet is intended to be practical enough for use by bridge design engineers. Variables in the design model include flange and bearing geometry, strand size and placement, effective prestress force, concrete and steel material properties, and the effects of steel bearing plates. The model is based on strut-and-tie and shear-friction concepts and considers the lateral-splitting failure mode. Derivation of the model is presented, and the model is compared with experimental results from the published literature.