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

Abstract eng:
Post earthquake reconnaissance reports illustrate that failure of reinforced concrete (R.C.) members often involve buckling of reinforcement, an observation suggesting that this phenomena is prerequisite for the necessary reduction of member length (shortening) that marks failure under transverse cyclic displacement reversals. From previous experimental research it is known that occurrence of buckling is linked to displacement history. In the present paper the problem of bar buckling in the plastic hinge region as a limiting factor of deformation capacity of reinforced concrete members is expressed, using as a vehicle the hysteretic stress−strain model of the reinforcement, in terms of the imposed displacement amplitude under cyclic reversals. Through the derived analytical expressions it is shown that when controlled by bar buckling, deformation capacity cannot be defined uniquely as it varies with the path of applied load. This explains in part the wide scatter of experimental results regarding drift capacity, which is particularly intense in cases where premature modes of failure are suppressed and the response is controlled by flexure. A corollary to this finding, which refers to the established procedures of displacement−based design, is that quantifiable indices of deformation capacity, associated with the various failure modes, need be expressed as lower bounds, to reflect the wide range of expected values as these might be limited by the occurrence of buckling of compression reinforcement under realistic earthquakes.

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