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

Abstract

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.

A review of FRP strengthened concrete structures under extreme loading

“…Yun et al (2008) showed that the post-fatigue bond strength under monotonic static load was not influenced by the fatigue damages if a sufficient intact bond length was still available. Similar observations were also reported by Ko and Sato (2007), Diab et al (2009) and Mazzotti and Savoia (2009). However, after high-level fatigue loading, the FRP-concrete has a significant reduction in the bond stiffness under monotonic loads (Yun et al 2008).…”

“…For the bending test, FRP rupture usually occurs near the transverse crack where high stress concentration is present (Xie et al 2015). FRP debonding is the most common failure mode for the FRP-concrete interface under cyclic loading (Bizindavyi et al 2003, Ko and Sato 2007, Yun et al 2008, Diab et al 2009, Mazzotti and Savoia 2009, Nigro et al 2011, Carloni et al 2012, Carloni and Subramaniam 2013, Xie et at. 2015.…”

“…A number of experimental and theoretical studies have been concerned with the fatigue load versus the loadedend slip response of the bond interface (Bizindavyi et al 2003, Ko and Sato 2007, Diab et al 2009, Carloni et al 2012, Carloni and Subramaniam 2013, Marinelli and Caggiano 2014, Carrara and Lorenzis 2015. These studies have shown that the stiffness of the bond load-slip response decreases as the number of fatigue cycles increases due to the propagation of fatigue damage along the interface.…”

“…It should be noted that when the bond length is larger than the effective bond length, the static bond capacity of FRP-concrete interface is constant (Chen and Teng 2001), but the fatigue life increases with the FRP bond length (Bizindavyi et al 2003) because a longer bond length takes more cycles for the fatigue crack to propagate. Based on experimental observations, the debonding process can be divided into three stages: rapid propagation, stable propagation and unstable failure (Diab et al 2009, Bizindavyi et al 2003. The first and second stage cover about 90% of the fatigue life.…”

“…It may be noted that Diab et al (2009) concluded that no failure occurred for specimens if the maximum fatigue loading is less than 60% of the static bond capacity of the FRP-concrete bond interface, but Iwashita et al's (2007) test results indicated that debonding failure occurred if the maximum fatigue loading was over 30% of the static loading capacity.…”