Research On Effects Of Temperature And Sustained Load On Bond Behavior Of Concrete Structure Strengthened With Near Surface Mounted FRP Reinforcement

The application of near surface mounted fiber reinforcement polymer (NSM FRP) strengthening system in civil and building construction is growing widely with many examples over the world. Main reasons for using this system are:it is possible to achieve a good strengthening effect with a relatively small work effort; effects of chemical environment, impacted force and fire on this system are less than other strengthening systems.Firstly, behavior of concrete structure strengthened with three FRPs strengthening systems will be introduced and analyzed. The main contents include failure modes of FRP strengthening systems due to flexural and shear failure; plate-end debonding; intermediate crack debonding or FRP rupture.Secondly, a pull-push concrete block strengthened by NSM FRP plate corresponding to different bond stress-displacement relationships is used to study the effect of sustained load on this strengthening system. Concrete-resin-NSM FRP plate bond performance is investigated in full characteristics of bond such as linear, bilinear, unilinear behaviors. In linear behavior, bond performance occurs in two stages:first stage, stress-displacement relation is expressed as a linearly ascending straight line; second stage, shear stress suddenly drops to zero. In bilinear behavior, bond performance occurs in four stages, including stages of elastic, elastic-softening, start-debonding and softening-debonding. In unilinear behavior, stages of propagation-softening, start-debonding in both long-short plate and end-debonding are mentioned in bond performance. Through studying the full characteristics of bond, the maximum load for a given FRP plate-concrete interface, the intermediate crack bond strength of interface, debonding strain resistance, strain distribution and maximum slip at the loaded end in FRP plate corresponding to the applied load can be determined.Besides, finite element (FE) analysis by Abaqus software is used to study more on bond performance. By simulation of concrete structure strengthening with NSM FRP in three-dimensions, transmissions of stress and slip from FRP to two layers resin and to concrete structure are analyzed. Intermediate crack debonding, strain distribution and slip at the loaded end in FRP plate or resin layers corresponding to the experimental load also are defined. The shear stress-slip relations at concrete-resin-FRP interfaces also are investigated. Theses results were compared with available tests and existing proposed model by other researchers. They are believed to have reasonable accuracy. Furthermore, the predicted failure mode of bond system by FE analysis is issued to compare with experimental failure modes.Thirdly, effect of temperature on the above bond performance is conducted into this thesis. It includes effects of temperature on components of NSM FRP system such as concrete, resin and FRP reinforcement. Besides, effects of high temperature and low temperature on system are separately studied. By above proposed parametric analyses method and finite element analysis method, two real design examples are calculated in detail to determine debonding resistance, strain resistance and strain distribution in NSM FRP bond system. The effect of temperature on NSM FRP strengthening system is defined by comparisons of results at both room temperature and low temperature (-26℃). Moreover, these calculating solutions are absolutely believable when they are compared with available experimental tests.