Reliability-Based Design Aid for Evaluation and FRP Retrofit of Existing RC Bending Members by Considering Project-Specific Conditions

This paper presents the formulation of a reliability-based design aid to assess the need for strengthening existing reinforced concrete (RC) flexural members and optimize the retrofit using externally bonded fiber-reinforced polymers (FRPs) if the member is deficient. The design aid consists of evaluation charts and a simplified formula calibrated using reliability theory to consider the effect of satisfactory past performance of the assessed structure in terms of load type and magnitude seen during the service life and the redundancy of the considered structural system. The design aid was calibrated based on the design procedure given in the American Concrete Institute ACI PRC-440.2-23, “Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures,” and the Canadian Standards Association CSA S806-12, “Design and construction of building structures with fibre-reinforced polymers,” and presented in a user-friendly manner to be used by engineers experienced in the assessment and retrofit of structures. The input of the design aid consists of the member’s unstrengthened utilization ratio (demand-to-capacity) and the number of hinges to form a mechanism, while the output is the required flexural resistance to upgrade the member capacity. Numerical examples of using the design aid in structural evaluation projects are presented, highlighting the significant savings in the required amount of FRP to retrofit deficient members compared to the conventional structural evaluation method.