Influence of damage in steel rebars with different yield strengths and compressive strength of concrete on longevity and ductility of RC beams under fatigue loading

Abstract

Influence of depth of induced damage in steel reinforcement bars with different yield strengths and compressive strength of concrete on longevity and ductility of RC beams under fatigue loading is reported. RC beams fabricated with four concretes of compressive strengths of 25, 35, 45 and 55 MPa combined with three types of steel reinforcement with yield strengths of 250, 415 and 500 were studied. The reinforcement bars were damaged with varying crack depths of 5.0, 5.5, 6.0 and 8.0 mm. The modes of failure and life of RC beams under fatigue loading established in terms of number of cycles (N) vs. mid-span deflection; load vs. mid-span deflection; normal strain vs. number of cycles; stiffness vs. number of cycles and crack lengths vs. number of cycles have been discussed. The magnitude of induced damage in rebars significantly influences the load carrying capacity and life of RC beams under fatigue loading, leading to conservative prediction of fatigue life. The fatigue life of RC beams with induced damage in RC beams with low yield strength steel reinforcement is greater than that of the High Yield Strength Deformed bars (HYSD ). Further, the fatigue performance of RC beams decreases with increase in the strength of concrete. Hence, the longevity and ductility of RC beams with low strength concrete and low yield strength reinforcement has been observed to be significantly improved.