Prestressed Cylindrical Shells after Cracking

The beam method and conventional ultimate flexural theory for prestressed concrete beams are used to predict the ultimate load of prestressed concrete cylindrical shell roofs of long and intermediate length. Tests on model shells, constructed of precast elements prestressed together longitudinally with draped and straight cables within the curved surface, show that the beam method gives an accurate or conservative prediction, provided the failure is in longitudinal flexure. The method assumes that the shell spans as a simply supported beam between cable ends, and it is essentially a linear elastic method. After cracking, even though the shell cross section tends to change shape, prediction of ultimate load based on the original shape will only be unconservative for long narrow shells of small structural depth which are likely to be unsatisfactory even in the uncracked range. The geometry of the five models varied between length/radius of two to three and a half included angle of 30? to 43—.