Colonnes elliptiques en béton armé confinées à l’aide de composites en PRF : simulations par éléments finis et études paramétriques

Abstract

This thesis presents research work that sheds light on the confinement mechanisms of concrete columns strengthened with FRP jackets and contributes to advancing the understanding of this efficient structural retrofitting technique. Today, this method has become an integral part of North American and European design codes. However, the complexity of such systems is reflected in these codes through limitations that are, at times, overly restrictive and, at other times, insufficiently conservative, potentially compromising structural safety. The general principle of confinement is like that of transverse reinforcement, as described in the unified model of Mander et al. (1988). Based on experimental and semi-theoretical models such as those developed by Teng and Lam (2002) and Chaallal et al. (2003), it can be deduced that the behavior of such columns depends primarily on the following key parameters: (1) the geometric shape of the column, which influences the uniformity of confinement, as highlighted by the studies of Hassan and Chaallal (2007) and Liu et al. (2023); (2) the number of FRP layers, their stiffness, and their tensile strength, which govern the confinement level and ductility of the column, as noted in the works of Benzeguir et al. (2024) and Gahmousse et al. (2021); and (3) the elastoplastic behavior of concrete and its compressive strength. Teng and Lam (2002) and Zeng et al. (2021) demonstrated that ovalization provides an effective solution for strengthening confined columns subjected to various types of loading. This system of FRP-confined elliptical columns was meticulously formulated using the Galerkin Finite Element Method for an accurate representation of their behavior under axial compression. The adopted formulation assumes small deformations and rotations, with nonlinearity arising solely from the concrete material. The plastic behavior of concrete was modeled using the Drucker–Prager yield criterion. The results obtained from the numerical simulations validate the experimental findings reported in the literature and lead to the development of an accurate analytical model that faithfully represents the influence of these parameters through a radial strut-and-tie model. The study reveals that the variation in the curvature of the concrete–FRP interface, the compressive strength of concrete, and the stiffness provided by confinement – governed by the intrinsic properties of the FRP and the number of layers – are integral components of the equations predicting the confinement stress and the load-bearing capacity of the structure, with a relative deviation of less than 10% to experimental results. Furthermore, potential improvements, particularly concerning the existing design code models, have also been proposed.

Date	8 Dec 2025
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Omar Chaallal (Supervisor)