Evaluation of Flexural Strength and Ductility of Hybrid Prestressed Concrete Members.

Flexural strength and ductility of exclusively bonded or unbonded steel prestressed concrete (PC) members are well covered and documented in the literature and codes of practice. However, current design methods are limiting the use of hybrid (that is, a combination of unbonded and bonded steel and fiber-reinforced polymer [FRP]) tendons, particularly when using brittle material such as FRP tendons. In this paper, a general procedure for evaluating the nominal moment capacity and ductility of hybrid PC members was developed using the strain compatibility approach. The procedure is applicable for members with any combination of bonded or unbonded steel and FRP tendons. Using capacity design approach based on strain compatibility, the ductility performance of several hybrid systems with different parameters were compared. The parameters included, among others, the level of "net tensile strain" in the tension reinforcement at nominal strength adopted in ACI 318-19 as a measure of ductility, concrete compressive strength, and the newly defined hybrid prestressing ratio (HPR). HPR represents the ratio of the moment contribution of the unbonded tendons to the total moment capacity of the member with hybrid tendons. Nonlinear analysis was carried out for generating the entire load-deflection and moment-curvature responses of the different systems. The accuracy of the nonlinear analysis was verified by comparing it with available experimental data, and the analysis results were used to compare traditional curvature ductility measures of the various systems against the ductility measure specified in the ACI Building Code. A design example is provided in Appendix A to illustrate the use of the strain compatibility approach. [ABSTRACT FROM AUTHOR]