Effect of steel fibers on bond performance of steel bars in NSC and HSC under load reversals

This study concentrates on experimental evaluation of the effect of fiber reinforcement on the bond response of steel bars under load reversals. Beam specimens with symmetrical spliced top and bottom steel bars were used in the investigation. The specimens were designed to experience splitting mode of bond failure. The test variables included the diameter of the spliced reinforcement d(b) or the ratio of concrete cover to bar diameter c/d(b), the concrete compressive strength: normal-strength concrete (NSC) and high-strength concrete (HSC), and the volume fraction of steel fibers. Without fiber reinforcement, the control specimens experienced very sudden and quick bond deterioration leading to a total loss of load resistance in the first cycle following bond splitting. The presence of steel fibers increased the peak bond strength, reduced the bond degradation or damage under cyclic loading, and resulted in substantially enhanced energy absorption and dissipation capacities. The level of improvement in cyclic performance increased with increase in c/d(b). Also, the increases in average bond strength at bond failure due to fibers were higher for the HSC when compared to the NSC specimens. Design equations in which the bond strength is expressed as a function of f(c)(' 1/4) were more accurate in predicting the test data for the plain unconfined specimens in comparison with f(c)(' 1/2). Available expressions for predicting the bond strength of developed/spliced bars in fiber-reinforced concrete showed good agreement with the test results.