Conservativeness in FRP-based structural strengthening design process

The fibre reinforced polymer (FRP) composites have proved to be effective for strengthening of existing concrete structures. However, the appraisal of the safety or conservativeness in the strengthening design process is more complex than it may first appear. This is due to the distinct characteristics exhibited by the FRP, such as lack of ductility and possibility of debonding-based failure modes. The conservativeness in particular context of the FRP-based strengthening design process is presented in this paper in the form that makes it possible to operate it mathematically. A comprehensive framework is presented that classifies the conservativeness involved in FRP-based structural strengthening into that applied on the material properties and that on the resistance contribution of the FRP. The conservativeness arising from same sources is presented in condensed form that makes it convenient to segregate and identify propagation of the conservativeness within the strengthening design process. The possibility of multiple failure modes of the externally-bonded FRP component is addressed through devising different conservativeness propagation paths, each representing a specific failure mode of FRP. It is shown that each of the possible conservativeness propagation paths is differently sensitive to the prescribed material conservativeness. Finally, the usefulness of the methodology in quantifying conservativeness is demonstrated for the case of FRP-based shear strengthening design process, for ACI440 and TR55 design guidelines. The methodology, however, can be applied to any guideline by appropriately calibrating it. The proposed methodology is a useful tool for fine-tuning and/or calibrating the design guidelines.