Kentaro Iwashita

Theoretical Solution for Fatigue Debonding Growth and Fatigue Life Prediction of FRP-Concrete Interfaces

This paper presents an analytical solution for the evolution and distribution of shear stresses along the entire bond length of FRP-concrete interfaces due to mode-II fatigue loading. The creep-fatigue interaction and fatigue crack growth after debonding initiation are incorporated into a nonlinear interfacial constitutive law. While the creep-fatigue interaction is represented by the degradation of the interfacial stiffness, the debond growth is governed by a form of the Paris equation and the fracture energy ratio, Gmax/Gc. Furthermore, a new form of energy ratio is adopted to be debond-dependent. Through a series of experimental double-lap shear specimens, the results showed that the debond growth rate (da/dN) along the FRP-concrete interfaces diminishes with fatigue cycles and that 30% of the static bond capacity of the FRP-concrete interface can be considered as the endurance limit of fatigue loading for FRP-strengthened beams. The agreement between the theoretical predictions and experimental results is valid, with a good degree of accuracy.

Strengthening Prestressed-Concrete Girders with Externally Prestressed PBO Fiber Reinforced Polymer Sheets

This study aims at developing an innovative strengthening system with externally bonded prestressed PBO (short for Polypara-phenylene-Benzo-bis-Oxazole) fiber reinforced polymer (PFRP) sheets, which present equal or higher strength and stiffness in comparison with high strength type of carbon fiber reinforced polymer (CFRP) sheets and great performance in energy absorption superior than other fiber reinforced polymer (FRP) sheets such as aramid and carbon FRP sheets. An experimental program was carried out to confirm the strengthening effects on load-carrying capacity, stiffness characteristics, ductility, and resistance of crack opening of prestressed concrete girders. The main parameters studied are the prestress level, the number of PFRP sheet layers, and resin impregnation of PBO fibers before or after sheet prestressing. An analytical study is also performed in order to investigate the flexural behavior of PC girders strengthened with prestressed PFRP sheets.

Bonding and debonding behavior of FRP sheets under fatigue loading

The purpose of this study is to improve the examining and understanding of the bonding behavior of Fiber Reinforced Polymer (FRP) sheets bonded to concrete blocks and steel plates under fatigue loading. First, a series of experimental investigations is summarized in the paper. The fatigue behavior of bonding surface between FRP sheets and concrete is finally characterized by the conducted P–S–N diagram representing the relationship among the probability of FRP debonding (P), the bond stress amplitudes (S), and the number of cycles (N) at debonding on a semi-logarithmic scale. The different debonding modes for various fracturing surface are also investigated and evaluated.

Structural Performance of RC Beams Strengthened with Prestressed Near-Surface-Mounted CFRP Tendons

This paper describes how fiber reinforced polymer (FRP) composites have been widely used as externally bonded reinforcements to strengthen or rehabilitate deteriorated concrete structures. However, premature debonding failure, due to the limitation of bond at the FRP-concrete interface,is often encountered, which limits FRP material potential for flexural strength increase. In order to minimize debonding failures and mechanical damage such as vehicular traffic and impact, etc., near surface mounted (NSM) FRP technology has emerged as another structural rehabilitation method. This study aims at evaluating a new strengthening using prestressed NSM carbon fiber reinforced polymer (CFRP) tendons. Although NSM FRP tendons are less susceptible to debonding than externally bonded FRP laminates, the load-carrying capacity of RC structures with NSM reinforcements is still likely to be governed by “premature” debonding failure. An experimental program with design variables such as prestress level and bonding agents was carried out to study the strengthening performance in terms of stiffness, cracking behavior and load-carrying capacity. The experimental results are presented and discussed in this paper. Experimentally validated bonding method is also proposed in this study.