Title:
Nominal Flexural Strength of Concrete Members Prestressed with Hybrid Tendons
Author(s):
Hani Nassif, Wassim Nasreddine, Gonca Ünal, and Mohamed Harajli
Publication:
Structural Journal
Volume:
123
Issue:
4
Appears on pages(s):
133-148
Keywords:
carbon fiber-reinforced polymer (CFRP); flexural strength; hybrid tendons; prestressed concrete (PC); ultimate stress; unbonded tendons
DOI:
10.14359/51749494
Date:
7/1/2026
Abstract:
The calculation of the nominal flexural strength of concrete members prestressed with hybrid (that is, a combination of bonded and unbonded [steel and/or carbon fiber-reinforced polymer (CFRP)]) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI 440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provision addresses the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the modified deformation-based approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without nonprestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI 440.4R stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-depth ratio, and loading applications.
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