EXPERIMENTAL STUDY ON THE MOMENT REDISTRIBUTION IN REINFORCED CONERETE FRAMES WITH HRB500/HRB600 STEEL BARS

To study the moment redistribution in the concrete frame beams reinforced with HRB500 and HRB600 steel bars, 12 single-layer and two-span reinforced concrete frames were tested. The test results showed that, due to the increase in the yield strength of the tensile longitudinal steel bars, the formation of the plastic hinges at beam ends was delayed. A certain extent of moment redistribution occurred before the formation of the plastic hinges. In addition, the strain penetration of the steel bars anchored in the joints caused larger additional rotations of beam ends, which increased the moment redistribution. The moment redistribution was investigated in two stages according to whether the plastic hinges were formed or not. The first-stage moment redistribution was between 10.35%~33.42% and the second-stage moment redistribution was between 3.39%~30.5%. Based on the test results, expressions for moment redistribution of the two stages were proposed. The first-stage moment redistribution decreased as a power function with an increase in the relative depth of the compression zone, and increased linearly as the yield strength of the tensile longitudinal reinforcement and the additional rotation at yielding increased. The second-stage moment redistribution increased as a power function with an increase in the total plastic rotation (the sum of the rotation of plastic hinges and the additional plastic rotation due to strain penetration), and decreased linearly as the yield strength of the tensile longitudinal reinforcement increased.