Calibration of Resistance Factors for CFRP Pretensioned and Post-Tensioned Bridge Girders

This paper presents a comprehensive reliability analysis of concrete bridge girders reinforced with bonded pretensioned and unbonded post-tensioned carbon fiber–reinforced polymer (CFRP) reinforcement. Recognizing the distinct mechanical behavior of pretensioned and post-tensioned girders, separate analyses were conducted to calibrate their respective flexural resistance factors. Both analyses were based on the widely accepted load model incorporated in the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications for girder design. For pretensioned girders, this study extends prior reliability research by updating the probabilistic parameters of the prestressing CFRP and recalibrating the professional factor using newly available experimental and numerical data. A flexural resistance factor of 0.75 is proposed for tension-controlled failure within the current AASHTO LRFD reliability framework based on the primary target reliability index of β = 3.5. The results corresponding to β = 4.0 are also reported as a conservative reference for less ductile CFRP rupture-controlled failure mode for a bridge structure with high importance and low redundancy. This work also marks the first reliability analysis in the literature for unbonded CFRP post-tensioned girders. A flexural resistance factor of 0.75 is recommended for compression-controlled failure, and because the unbonded CFRP tendons experience limited stress increase under flexural action, tension-controlled failure is difficult to achieve and therefore it was not considered in this study. These results provide guidance for the design of CFRP-prestressed concrete girders, contributing to advancements in bridge engineering and the implementation of CFRP in structural applications.