Hysteretic energy and damping capacity of flexural elements constructed with different concrete strengths

In rigid frames, performance during major earthquakes requires plastic hinges to form at beam-ends, and for them to have sufficient energy and damping capacity to accommodate the earthquake energy. An experimental program was carried out to investigate those characteristics for beams constructed with target concrete strengths of 30, 70, 150 MPa. Other variables were studied including: the bottom/top reinforcement ratio (0.33, and 1.0), the ratio of transverse reinforcement (0.8, and 1.6%), and the shear span to depth ratio (2.0, and 3.0). The test specimens were designed to represent the behavior of an exterior beam–column connection in a ductile moment-resisting frame. The beam tip was subjected to cyclic displacements that caused significant inelastic damage. Different energy and damage indices were used to explore the effect of concrete strength on the hysteretic energy and the damage index. The damping has been evaluated as an equivalent viscous damping ratio. Despite the increase in brittleness of the concrete due to the increase of concrete strength, the hysteretic energy capacity of beams may be improved by increasing the concrete strength. However, this effect cannot be generalized because it is strongly influenced by the other variables. The energy capacity can be significantly improved by reducing the shear demand, and increasing the ratio of bottom reinforcement. An increase in transverse reinforcement enhances the capacity for energy dissipation but to a lesser degree. The viscous damping ratio is significantly influenced by the amount of bottom reinforcement, and slightly influenced by the transverse reinforcement ratio and shear demand level.