Bond behavior of helically wound FRP bars with different surface characteristics in fiber-reinforced concrete

Bond behavior of fiber reinforced polymer (FRP) bar in concrete is critical for structural performances. This study investigates the effects of bar type, steel fiber content and surface characteristics on the bond behavior of FRP bars. Pull-out tests of basalt and glass FRP bars with different rib heights (smooth, shallow and deep) were conducted in concretes with various steel fiber contents (0%, 1.0% and 1.5%). Experimental results indicate that bond strength of FRP bars is significantly affected by the height of rib. The bond strength can be significantly increased from less than 2.5 MPa to 30 MPa by increasing rib height from 0 to 0.76 mm. The inclusion of 1.0% steel fibers in volume can prevent the splitting failure. A novel bar geometry-based model for calculating the bond strength of helically wound FRP bars is proposed by combining the experimental data in this study and existing data in literatures.