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The lateral deformation behavior of a RC column is particularly important because it not only magnifies the moment but also affects the ability of the column-and, subsequently, the frame-to sway and absorb energy at all stages of loading. The lateral deformation is affected by disturbed regions, such as tensile cracks or compression wedges, which are often simulated with the help of hinges whose properties are derived empirically. Being empirical, these hinges can only be used within the bounds of the tests from which they were derived, and in this respect are of limited use. In this paper, a mechanics-based hinge is developed that can be used at all stages of loading (that is, at serviceability through to ultimate) and also during failure. The mechanics-based model is based on the principle of plane sections remaining plane, shear-friction theory that quantifies the behavior of RC across sliding planes, and partial-interaction theory that allows for slip between the reinforcement and the encasing concrete. Being mechanics based, it can be used for any type of RC column; that is, for any type of reinforcement and for any type of concrete as long as the material properties are known. The mechanics model is shown to be in good agreement with published test results and can simulate not only multiple cracks if necessary but also the formation of wedges. [ABSTRACT FROM AUTHOR]

Shear friction or aggregate interlock behaviour across sliding planes in concrete is a well-established area of research used in numerical modelling and in the understanding of shear failure. Much of the research has been done on initially cracked planes. In this paper, both the shear stress ( ) and the crack separation (h) of the shear friction parameters for both initially cracked and uncracked concrete sliding planes are quantified mathematically in terms of the displacement (∆) of the sliding plane, the compressive strength of the concrete (f) and the normal stress ( ) across the sliding plane. A bound to these generic shear friction parameters ( , h, ∆ and ) for both initially uncracked and cracked concrete is also developed. [ABSTRACT FROM AUTHOR]

Abstract: When a concrete member is subjected to a load its response is both instantaneous and time dependent. The influence of time dependent deformation is particularly import because it may lead to serviceability failures in structural members where deflections or crack widths are excessive. Current analysis techniques for reinforced concrete members are built around a moment–curvature (M/χ) approach that is based on the assumption of full-interaction (FI), that is, the reinforcement does not slip relative to the concrete which encases it and, consequently, the widening of cracks and their effect on deflection cannot be simulated directly. Hence in order to determine member deflection, empirically derived expressions for the flexural rigidity of a member (EIemp) are required to allow for the tension stiffening associated with cracking. In contrast to this FI M/χ approach, a moment–rotation (M/θ) approach has been developed which allows for slip between the reinforcement and concrete, that is partial-interaction (PI) and which, consequently, obviates the need for the empirically derived flexural rigidities (EIemp). The PI M/θ approach simulates directly, through partial-interaction structural mechanics, the formation and widening of cracks as the reinforcement pulls from the concrete at crack faces and, consequently, automatically allows for tension stiffening. Hence the PI M/θ approach is a useful improvement of the current FI M/χ approach as it quantifies the flexural rigidities associated with tension stiffening which can then be used in standard analysis techniques. It is also shown in this paper that the moment rotation approach can be used to derive flexural rigidities that account for the long term effects of creep and shrinkage as well as predicting the effects of creep and shrinkage on cracks widths and spacings. [Copyright &y& Elsevier]