COMPREHENSIVE DESIGN-ORIENTED MODEL FOR FRP-CONFINED CIRCULAR RC COLUMNS

Abstract

Today, the use of fiber-reinforced polymers (FRPs) for the confinement of reinforced concrete (RC) columns is a state-of-the-art technic in the strengthening of existing structures. Thus far, various design models are present in literature to predict the stress-strain behavior and to allow for the ultimate limit state design of FRP-confined concrete. Often, the models proposed are scientific in nature only, they are just designed for plain concrete specimens, and they do not meet the demands necessary for practical use. Therefore, this paper presents a comprehensive design-oriented model for FRP-confined circular RC columns considering both the ultimate limit state (ULS) and the serviceability limit state (SLS). Beside equations to calculate the new ultimate confined concrete strength and the accompanying axial strain, the paper introduces an approach to generate a stress block simplifying the design procedure for columns subjected to combined compression and bending. Furthermore, an equation is presented to allow for the calculation of a combined partial safety factor taking into account the material safety factors of both the concrete of the column and the FRP system used. In order to realize a proper and coherent limit state method, the entire model uses characteristic material values and equations only. At last, the SLS is addressed with a simple approach limiting the maximal concrete compressive stress.