FLEXURAL BONDING CHARACTERISTICS OF NEWLY-DEVELOPED GFRP REBAR

Nowadays, glass fiber reinforced polymer (GFRP) rebar has been received lots of attention as an alternate reinforcing material to the concrete structure. The bond capacity between concrete and reinforcing bars is one of the main characteristic of reinforced concrete structures. To evaluate the bonding characteristic of the GFRP rebar, one-way pull-out test have been performed by many researchers. But this kind of research may not be reasonable to investigate the flexural bonding performance for serviceability of the concrete flexural member reinforced with the GFRP rebar. In this study, the flexural bond strength of beam reinforced with the newlydeveloped GFRP rebar was evaluated under 4-point static and fatigue bending. For the flexural bonding test, the British Standard for flexural bonding was applied. This shape was fabricated to have concrete compressive block and semi-circle hollow with the GFRP rebar at the middle section of beam. It can simulate the ultimate state condition for reinforced concrete structure for bending. The variables were made to have bonding length of 5times (5db), 10times (10db) and 15times (15db) of the nominal diameter of GFRP rebar and the relationship between the bonding strength and the slip was analyzed. In the result of test, two failure patterns were investigated. For static test, pull-out failure pattern was dominant in the 5db specimen and concrete tensile failure pattern was appeared in the 15db specimen. In the result of fatigue test, the number of loading cycle was decreased as the stress level was increased until failure. And also, as the embedment length was increased, the number of loading cycle was increased too. For the S-N relationship, the fatigue limit of the GFRP rebar was found to be around of the stress level of 70%. From these test results, the fatigue life was suggested as linear equation based on the Miner’s theory by applying regression procedures with the fatigue test results. Flexural bonding characteristic of GFRP rebar be able to be adapted for GFRP rebar design and analysis to the concrete structure.