Review and Comparison of Fracture Mechanics-based Bond Strength Models for FRP-strengthened Structures

Abstract

This study presents a critical review on fracture mechanics-based bond strength models related to the use of externally bonded fiber reinforced polymer (FRP) composites in the rehabilitation of concrete. The predictions from a set of typically used bond strength models are compared with each other through a set of parametric studies. Given that the models use a diverse set of parameters, in order to enable an equitable comparison, parameters are carefully chosen as related to (a) characteristics of concrete, (b) characteristics of the FRP, and (c) characteristics related to concrete cover and epoxy mortar. The corresponding reliability and accuracy is also confirmed by comparing with test data. A comparison of some of the major models in this class with experimental data shows that the accuracy in prediction of P_max and L_e varies substantially with very few of the models actually incorporating the effects of critical bond parameters such as adhesive thickness and characteristics of the FRP–concrete interphase. Furthermore, the direct application of the results of these models into a sectional analysis provides an underestimation of the capacity of FRP-rehabilitated RC beams, with the exception of the ACI-440 approach which in most cases overpredicts results indicating its non-conservative nature. The use of procedures recommended in ACI-440 and as proposed herein are shown to provide a more accurate description, with the latter providing a means of determining the mode of failure through incorporation of the energetics of fracture interaction between cracking in concrete and redistribution of forces to the FRP. Critical aspects still needing study are also identified.

Keywords

fiber reinforced polymer (FRP)rehabilitation bond strength effective length maximum capacity interfacial fracture energy fracture mechanics failure mode

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