Research On Width Effect And Snap-Back Of FRP Externally Bonded To Concrete

In resent twenty years, external bonding with fiber-reinforced polymer(FRP) is one of the most popular methods for the rehabilitation of concrete structures. The debonding between FRP and concrete interface usually govern s the behavior of the rehabilitated structures, so the performance of the FRP-to-concrete interface is a basic and difficult problem. How to determine the value of width effect in external ly bonded FRP system and how to explain the snap-back phenomenon in loading procedure become two important and difficult problems which have puzzled researchers in the past.The first two chapters in this thesis review the tests, failure modes, bond strength modes and bond-slip relationship modes of external bonded FRP to concrete system. All of the bond strength modes and bond-slip relationship modes in literature and the differences among different models are summarized and described in details.Based on the literature about externally bonded FRP system, a database with 865 externally bonded FRP specimens is established in the third chapter in this thesis, which is the biggest database in this field. Among the 865 specimens, 65 specimens with a two-direction stain field are used to analyse the width effect of the externally bonded FRP joints. Based on the analysis, the author derived the width effect model and bond strength model which are effected by elastic modulus of FRP, thickness of FRP, bond length, width of FRP, width of concrete and compressive strength of concrete. After comparing the new model with the previous models, it is found that the new model predicted the test results better.The fourth chapter in this thesis establishes an analytical solution considering the snap-back phenomenon which caused an unloading and reloading process in the curve of bond-slip relationship. This analytical solution can explain the snap-back occurrence, snap-back procedure and influence area very well. By comparing the analytical results with test data, it is found the analytical solution in this thesis not only predicts the test data well, but also can explain the phenomenon of strain fall near the loaded end in the externally bonded FRP joints.