Bond degradation of glass fibre reinforced plastic bars in concrete subjected to tensile cyclic loads

An adequate bond between reinforcement and concrete is critical in ensuring the composite behaviour of a reinforced concrete structure. Although fibre reinforced plastic rebar-concrete bond behaviour under monotonic load has been studied by many researchers, little is known about its behaviour under repeated loads. In this study, a series of pull-out tests were performed to investigate the bond stress-slip behaviours under tensile cyclic loads at local slips greater than elastic range. Conventional reinforcing steel bars and two common types of glass fibre reinforced plastic bars, embedded in concrete with strength of 42 MPa, were tested under four different loading patterns (monotonic + 3 tensile cyclic load patterns), and the bond failure of each specimen was examined. The results indicate that the bond strengths of fibre reinforced plastic rebar, unlike steel rebar, can be affected by as much as 24% by tensile loading history. In addition, the analysis of the failure surfaces of the rebar after the tests showed that bond strength degradation of the glass fibre reinforced plastic rebar types considered in this study can be attributed to the degree of interlaminar failure.