Torsion Experiment and Cracking-Torque Formulas of Prestressed Concrete Beams

摘要

Previous torsion experiments on prestressed concrete (PC) beamshave various limitations. A new experimental project was thereforeconducted to test seven PC beam specimens under pure torsion.This new torsion test o f PC beams achieved accurate measuremento f small twists before and around cracking, and improved otheraspects, including precise measurement o f prestressing forces andprestress transfer. The test also enabled assessment o f relativelylarge specimens with medium to high prestress levels and highconcrete strengths. Experimental results from seven specimens arepresented in this paper. The experimental values o f cracking torqueTcrfo r the seven specimens, and fo r another 12 specimens from aprevious experiment, are compared with the Tcr values calculatedusing a recently developed rational formula fo r reinforced concrete.Using these comparisons, a new Tcr formula fo r PC beams withconcentrated or distributed tendons is proposed, which accuratelypredicts the cracking torques o f the 19 specimens.