Abstract
In order to improve the efficiency of fiber reinforced plastics (FRP) confinement as a method to repair and strengthen concrete structures, a parametric analysis was carried out to investigate the effects of cylinder slenderness and the stiffness of the confinement on the localization pattern, the stress–strain response and the effectiveness of the confinement. FRP-wrapped concrete cylinders under axial compression were modeled in a high-resolution finite element model. Concrete was modeled as a Mohr–Coulomb material. The bi-linear stress–strain structural responses concur with published experimental data. Localization along discrete shear planes results in a failure mechanism that causes non-uniform hoop stresses in the FRP wrap due to the movement of solid wedges in the mechanism. A characteristic length for localization was identified and found in agreement with published experimental observations. The confinement efficiency shows a clear dependence on the confinement level and a weak dependence on slenderness above the characteristic length. A simple mechanistic model is proposed for the second branch of the bi-linear stress–strain response curve. The results of this study can be used to estimate the confinement efficiency factor and refine the design recommendations of Equation 12.1 of ACI 440.2R17.
Highlights
The confinement of reinforced concrete columns in aging infrastructure with multiple layers of fiber reinforced plastics (FRP) has gained wide acceptance as a repair and strengthening method and considerable experimental and theoretical research has been devoted to the topic during the last 30 years
Jansen and Shah [67] carried out an experimental investigation on compression failure localization in normal- and high-strength concrete cylinders with H/D ratios going from 2 to 5.5, reporting that the total length of the failure zone of the longer specimens became consistent at about three times the specimen diameter
Wei and Wu [29] examined, experimentally, the localized failure in confined and unconfined concrete columns of 150 mm in diameter, with H/D going from 2 to 4.66 at six different levels of confinement. They confirmed the localization of failure and the development of a failure zone. They observed that post peak deformation is independent of H/D for ratios greater than two and proposed a new analytical stress–strain model that accounts for localization and calculates the length of the failure zone [72]
Summary
The confinement of reinforced concrete columns in aging infrastructure with multiple layers of fiber reinforced plastics (FRP) has gained wide acceptance as a repair and strengthening method and considerable experimental and theoretical research has been devoted to the topic during the last 30 years. International and national organizations have issued standards and technical recommendations for the use of FRP wraps to reinforce concrete columns, such as in ACI 440.2R17 [1] and CS806 [2], reflecting the state of the art. The strengthening effect is achieved by the passive resistance that the elastic FRP confining wrap offers to the lateral expansion of concrete under compression. Sci. 2020, 10, 3432 multiple research efforts, no unified model has been established to predict the stress–strain response of FRP-confined concrete or to predict its failure strength
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