Simplified Modeling of Concrete Confinement (original) (raw)

The goal of this research project is to model the effect of confinement on concrete members by means of externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes for reinforced concrete columns are considered herein, namely circular, solid and hollow, square and rectangular. Nowadays innovative materials are developing focusing on the sustainability of the intervention, improving "traditional" FRP materials, where the organic matrix is substituted by an inorganic matrix and fiber fabrics are substituted by biaxial grids, while almost the same fiber materials are adopted. The simplified model is practitioners and code oriented, while it is derived from a more research oriented refined iterative confinement model proposed by the same authors to evaluate the entire stress-strain relationship of confined concrete. Based on a detailed analysis of the stress state, a simplified closed form solution is proposed to account for the non-uniformly confined concrete performance exhibited in non-axisymmetric sections. The non-uniform confining stress field exhibited in such cross-sections is explicitly considered by means of the mean value integral of the pointwise variable stress state over the cross-section. The key aspect of the proposed methodology is the evaluation of the effective equivalent pressure to be inserted in a triaxial confinement model, to account for the peculiarities of square and rectangular cross-sections. Experimental data, available in the literature and representative of a wide stock of applications, were compared to the results of the theoretical simplified model to validate the proposed approach, and satisfactory results were found.