Load-History Effects on Deformation Capacity of Flexural Members Limited by Bar Buckling

Buckling of reinforcement is one of the possible phenomena that limit the deformation capacity of reinforced concrete members under reversed cyclic loading. Previous experimental research suggests that occurrence of buckling is linked to displacement history, a parameter that is not explicitly accounted for in the available expressions for ultimate drift or curvature ductility capacities. This problem is explored in the present paper, by following through analytical expressions that relate the critical buckling strain as defined by the hysteretic stress-strain model of the reinforcement and the imposed cyclic history in terms of displacement. The analytical expressions thus derived are evaluated parametrically in order to establish behavioral trends. It is shown that when controlled by bar buckling, deformation capacity cannot be defined uniquely as it varies with the path of applied load. A primary conclusion of the research is that any quantifiable indices of deformation capacity referred to in the framework of displacement-based design using deterministic approaches need be adjusted to represent conservative lower bounds rather than approximations to the actual values of nominal failure.