Low-cycle fatigue performance of high-strength steel reinforcing bars considering the effect of inelastic buckling

A comprehensive experimental study was carried out to examine the low-cycle fatigue performance of ASTM A1035 Grade 690 rebars under cyclic-strain reversals with total strain amplitudes ranging from 1% to 4%. 12.7and 15.8-mm diameter unmachined rebars were tested. To evaluate the effect of inelastic buckling on the lowcycle fatigue performance, bar unsupported length was varied between 6db and 15db in 3dbincrements, where db is the bar diameter. Rebar buckling was not completely prevented even in specimens with bar unsupported length of 6db, hence cyclic stress-strain responses were unsymmetrical for all the specimens. However, decreasing the strain amplitude and bar unsupported length generally increased the fatigue life and total energy dissipation of ASTM A1035 Grade 690 reinforcing bars. Existing strain and energy-based fatigue-life models? constants were calibrated using the generated experimental fatigue data. The proposed models are applicable to ASTM A1035 Grade 690 rebars subjected to cyclic-strain reversals with total strain amplitude ranging from 1% to 4%. The results revealed that utilizing the previous fatigue-life models with constants calibrated using data obtained from tests on other types and grades of steel with nearly identical monotonic tensile stress-strain responses compared to that of ASTM A1035 Grade 690 steel would lead to inaccurate fatigue life predictions. The effect of inelastic buckling was incorporated into the proposed models by correlating their constants with a buckling parameter. Based on the proposed models? predictions, ASTM A1035 Grade 690 reinforcing bars were found to have the potential to be used in reinforced concrete columns designed for a maximum target ductility demand of 2 provided that the center-to-center spacing between the transverse reinforcements is limited to 6db.