Abstract
The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) 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 (RC) columns are considered herein, namely square and rectangular. The simplified model is derived from a more 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 through Mohr’s circle, 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 any 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.
Highlights
Within the applications of composites in construction, the confinement of reinforced concrete (RC)columns is one of the most common
The first models proposed at the beginning of last century were based on the Coulomb plasticity criterion (e.g., [6]), so they were based on solid mechanics
It was highlighted that the Coulomb plasticity criterion was very simple, because it proposed a linear relationship between lateral confining pressure, fl, and confined concrete strength, fcc, both normalized by unconfined concrete strength, fco (Equation (1)), needing the evaluation of a constant, k1
Summary
Within the applications of composites in construction, the confinement of reinforced concrete (RC)columns is one of the most common. Confinement studies date back to early 20th century; only in last few decades have extensive experimental and theoretical research documented fiber reinforced polymer (FRP) confinement efficiency (a theoretical background can be found in Di. Ludovico et al [1], and a comprehensive updated state-of-the-art on a large amount of confinement tests and models is presented in Ozbakkaloglu et al [2] and Pham and Hadi [3]). Ludovico et al [1], and a comprehensive updated state-of-the-art on a large amount of confinement tests and models is presented in Ozbakkaloglu et al [2] and Pham and Hadi [3]) For both building columns and bridge piers, the strengthening using FRP strips ensures an easy and fast installation, a strength and/or ductility increase, a high durability, low impact on the use of the structure and almost no increase of mass and geometrical dimensions of the members. Regression analyses of the experimental results led to models mainly based on the form reported in Equation (3), where the constants, a and b, are determined according to the best fitting of the experimental data (and sometimes, a and b can be expressed as functions depending on different parameters)
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