Currently there is only a singe input for concrete density in the prestressed girder design module. This density is used to calculate the weight of the beam and also the E modulus. There should be 2 separate inputs for density. One would be used for the concrete itself and would be used to calculate the E modulus of the concrete. The other density should be used to calculate weight of the reinforced concrete beam. For example, in a typical bridge, I would use 145 pcf to calculate the stiffness of the concrete. I would use a density if 150 pcf to calculate the combined weight of the concrete and reinforcing steel. The program should accommodate both inputs. This is typical practice in many other design programs.