Ductility analysis of prestressed concrete beams with unbonded tendons

This paper describes a numerical method for the full-range analysis of prestressed concrete flexural members with unbonded tendons, taking into account the stress-path dependence of materials. The numerical results compare favourably with experimental results. Parametric studies are carried out to evaluate the influence of loading type, span–depth ratio, combined reinforcement index (CRI), partial prestressing ratio, concrete compressive strength, and ratio of compressive reinforcement, etc. on the ductility behaviour. The results indicate that the curvature ductility factor of prestressed concrete members with unbonded tendons decreases with the increase of CRI. The curvature ductility factors for members with bonded and unbonded tendons for given values of CRI are also analyzed and compared. It is generally observed that when the CRI is between 0.15 and 0.20, the ductility factor of an unbonded member is close to that of the bonded one. Above this range of CRI the ductility factor of an unbonded member is higher than that of a bonded one, while below this range the ductility factor of an unbonded member is lower than that of a bonded one.