Examining the Effect of Load Type and History Using Reliability on Optimizing the Design of FRP-Strengthened RC Members in Flexure

Abstract

There is an increasing need for optimizing the design of fiber reinforced polymer (FRP) flexural strengthening of deficient concrete beams. Optimizing the design is crucial for enhancing the competitiveness of FRP material as compared with conventional environmentally unfriendly materials like concrete and steel. Practicing engineers in Canada are often faced with design challenges when applying the current codes and standards (NBCC 2015; CSA S806-17) to strengthen existing buildings, including the high amount of FRP material required to strengthen existing deficient members. These challenges often result in practicing engineers selecting more financially viable conventional retrofit options, like shortening existing spans with steel posts. In this study, a simple reliability-based method is used to generate user-friendly design charts, to optimize the amount of FRP layers required to strengthen concrete beams, deficient in flexure. These charts are derived to be compatible with the Canadian building codes (NBCC 2015; CSA S806-17). A database of experimentally tested strengthened beams is collected, applied along with the statistics for unstrengthened beams and loads, used to calibrate the NBCC and ACI 318 codes, respectively, to run the reliability analysis. Results show that the code generally prescribes an over-conservative amount of FRP for a given target safety and that when accounting for load type and history, the reliability method can meet the same target reliability index with less material.