Uncertainty analysis of strength and ductility of confined reinforced concrete members

The strength and ductility of reinforced concrete beam and column cross-sections with varying geometries and levels of confinement are investigated. Material properties are modelled as random variables and their effect on section behaviour is assessed through fibre modelling and the Response Surface Methodology. The section ductility is in many cases found to be mainly dependent on the ultimate concrete strain. The uncertainty involved in the estimation of the latter using various models for confined concrete is examined with the aid of existing experimental data. Other failure criteria such as first hoop fracture and buckling of the longitudinal bars are also considered. Monte Carlo simulations show that a significant amount of variability exists in both the strength and ductility of confined concrete sections due to variations in material properties. In the case of ductility, this variability is greatly enhanced if model uncertainty is taken into account, especially for high axial loads. Furthermore, simple expressions are derived for the estimation of the strength parameters for any cross-section subject to varying material properties. Finally, the confined concrete model and curvature ductility provisions of Eurocode 8 are evaluated.