Damage evaluation of RC beams under variable amplitude loading histories

Based on the variable amplitude loading tests of 22 RC beam specimens with different stirrup ratios and reinforcement ratios, deterioration characteristics and corresponding prediction methods of energy dissipation capacity, loading capacity and loading stiffness for RC beam under variable amplitude loading histories were investigated. A seismic damage index was proposed to discuss the effects of maximum displacement, cumulative hysteretic energy and loading history on the damage. The research shows that, for RC beams under variable amplitude loading histories, the increasing of decay indexes for energy dissipation capacity, loading capacity and loading stiffness is not fully synchronized, but the three indexes are all related to the historic maximum displacement and the cumulative hysteretic energy. The increase of decay indexes for energy dissipation capacity and loading capacity with hysteretic cycles are non-monotonic increasing, but that for loading stiffness is monotonically increasing. Therefore, the decay index of loading stiffness is more suitable for damage evaluation. When the ductility coefficient of the RC beam is small (μk, max<3), the damage of the component is positively correlated with the ductility. The cumulative hysteretic energy and the maximum displacement appear to have little influence on this positive correlation, and the increase of the stirrup ratio can significantly reduce the damage under the same ductility conditions. Therefore, controlling the ductility coefficient and improving the stirrup ratio is a stable and effective way to control the seismic damage of RC beams. © 2017, Editorial Office of Journal of Building Structures. All right reserved.