Design implications of increased live loads on continuous precast, prestressed concrete girder bridges

Precast, prestressed concrete girders are often made continuous to support live loads and composite loads. Although American Association of State Highway and Transportation Officials (AASHTO) HL93 loads are adopted internationally, it is common practice in industrial zones where oversized/overweight trucks are the norm to design for greater live loads. The British Standards Institution's live loads can be as much as 50% higher than the HL93 loading and are therefore sometimes used in design. This paper investigates the implications of increased live loads on the design of precast, prestressed concrete girders made continuous. The increase in positive moments due to increased live load is economically accommodated by increasing the prestressing force. However, this leads to overstress in the girder end zones over the intermediate supports. Recommendations for reducing these stresses by using debonded strands in excess of the 25% limit imposed by AASHTO are made by making the flanged section solid at its ends to increase the shear capacity locally.