The untopped double-tee floor member shown in fig. 6-24, spans 46 ft(14.0 m) in an office building and carries a service live load of 50 psf (2.4 kN/m2) as well as superimposed dead load of 15 psf (0.72 kN/m2)
The concrete strength at transfer, f ‘ci, is 3500 psi (24.1 MPa), and the minimum specified 28-day strength is 5000 psi. (34.5 MPa) (normal weight concrete). The prestressing is ½ in. (13 mm) diameter low-relaxation strand, with an ultimate strength,fpu= 270 ksi (1860 MPa), which will be tensioned to 0.75fpu in the pretensioning bed. Desigh the double tee following the conventional practice of using only prestressing strand for longitudinal reinforcement in the stems.