Behaviour and analysis of confined concrete

It is widely recognized that concrete strength and post-peak ductility depend upon the level of confinement. Brittle or ductile behaviour is a function of triaxial compression, unconfined concrete strength, volumetric expansion, and softening.; A comprehensive study of confined concrete is carried out. The effects known to have influence on its behaviour are studied through analyses of an extensive experimental database. A stress-strain curve for concrete in compression is proposed that accounts for three-dimensional effects. The pre-peak response is predicted utilizing the formulation proposed by Hoshikuma et al. (1996). The load carrying capacity of confined concrete is predicted utilizing the Ottosen surface with newly developed coefficients that account for a wide range of confinement levels (lateral pressures up to 100% of the unconfined concrete strength). Unconfined concrete strengths from 20 MPa to 130 MPa are considered. Concrete dilatation is modeled as a function of the lateral pressure ratio (lateral pressure to unconfined concrete strength) and concrete strength, beyond the incompressible limit (Poisson's ratio of 0.5). The strains at peak strength and at 80% of peak strength in the post-peak regime are also proposed as functions of the stress state. A new post-peak curve that accounts for brittle or ductile behaviour is also proposed.; The proposed models were corroborated at the material level with experimental results of concrete subjected to active or passive confinement, yielding accurate agreements regardless of the load paths. The models were implemented in two of the VecTor series of programs developed at the University of Toronto; VecTor3 for three-dimensional analysis of reinforced concrete solids, and a new program, developed for this work, VecTor6, for analysis of axisymmetric solids.; Analyses of confined concrete at the structural level were performed using compression field modeling of confined concrete (Montoya, Vecchio, and Sheikh 2001), a methodology for nonlinear elastic analysis that combines models from the modified compression field theory (Vecchio and Collins 1986) and models derived empirically and from plasticity approaches. Columns confined with FRP composites or steel were analyzed. The ability of the proposed constitutive models to accurately determine the peak strength, concrete dilatation, pre- and post-peak regimes is verified.