Eccentrically Prestressed Box Girders
Under Combined Bending and Torsion
Barrington deV. Batchelor and W. Douglas McEwen
Appears on pages(s):
beams (supports) ; bending; bending moments;box beams; cracking (fracturing); failure; girders; prestressed concrete: prestressing steels; pretensioning; structural analysis; torsion; torsion tests.
An investigation of bending-torsion interaction in eccentrically prertressed concrete box girders is reported. The ten specimens tested were under-reinforced in the longitudinal and transverse directions, and were prestressed initially so that extreme fiber stresses were up to the limits allowed in practice. The only intentional variable in the study was moment-torque ratio which was varied over the range of zero to infinity. Bending-torsion interaction at first cracking was closely predicted by a parabolic equation proposed by Cowan for sections without transverse reinforcement. Interaction at ultimate conditions conformed closely to parabolic relationships, proposed by other investigators, for use with under-reinforced rectangular sections. However, certain redefinitions of terms are necessary.to make the existing interaction equations applicable to sections with high eccentric prestress. A procedure, incorporating these modifications, is presented for developing interaction diagrams for girders of the type studied.