Fabrication and Design of Precambered Precast, Prestressed Concrete Bridge Girders

Abstract

■ This paper discusses fabrication, girder design, and shipping and handling considerations for precambered bridge girders. Building an intentional vertical curve into a precast concrete girder formwork system and the prestressing strand layout creates a girder with a prefabricated vertical curvature known as precamber. Precamber is the sum of the natural camber due to girder self-weight and eccentricity of the prestressing force plus the curvature built into the formwork (hereafter called formed camber). Precamber is an effective technique for matching the roadway profile grade for girders fabricated with a monolithic deck slab. For superstructures with a cast-in-place (CIP) concrete deck, this technique helps meet challenging vertical clearance requirements and reduces the slab haunch buildup associated with significant vertical curve profiles. Figure 1 shows a girder fabricated with substantial crest precamber to provide vertical clearance under the span. Girders have also been cast with sag curvatures to match required roadway profile grade.