Stirrup design for critical lengths of reinforced-concrete structural members

Abstract

It was long ago stated by Priestley, and now applies more than ever, that the design of reinforced concrete is so full of myths, fallacies and contradictions that it is hard to know where to begin in an examination of current design. Such an examination forms the subject of the present paper, with a focus on current methods for designing stirrup arrangements for confining the transverse expansion of concrete in the compressive zone of the critical lengths of structural concrete members. These methods have often been found inapplicable in practice and the reason for this is attributed to the misconception that the structural performance code requirements can only be satisfied by confining the transverse expansion of concrete with an appropriate stirrup arrangement. It is argued that stirrups are required for securing a mechanism of load transfer, rather than for producing confinement, within the critical length when bond between concrete and steel is lost after yielding of the flexural reinforcement in tension. A method for assessing the stirrups required for this purpose is proposed and shown to produce design solutions that not only satisfy the structural performance code requirements but also are free of the shortcomings of current methods.