Based on a linear programming mathematical model, a set of charts has been developed to carry out a preliminary design of precast, prestressed concrete box girder bridges. The first chart shows the girder capacity expressed as a curve, furnishing the maximum span for a given girder spacing or alternately the girder spacing for a given span. Once the most economical girder has been established, the remaining charts can be used to determine the minimum required prestressing force for an interior girder. The mathematical model is also used to conduct a parametric study to evaluate the effect of allowable tensile stresses at service load, girder concrete strength and variations in deck thickness on the maximum span of girders at a given spacing and the required prestressing force. A numerical design example, conforming to AASHTO Specifications, is included to illustrate the design procedure and use of the design aids.
