Incremental Plastic Analysis of Confined Concrete Considering the Variation of Elastic Moduli

Experimental studies have demonstrated that the elastic moduli of concrete, specifically Young’s modulus and Poisson’s ratio, undergo changes during compressive loading. Despite the fact that variations in Young’s modulus are frequently considered in nonlinear analyses, Poisson’s ratio is typically assumed to be constant, which has a direct impact on confinement modeling. In this research project, an attempt was made to enhance the accuracy of predicting the behavior of concrete columns confined by AFRP and CFRP by considering the variation of elastic moduli of concrete during loading. To account for the changes of Poisson’s ratio, an approximate method was proposed that involves assembling a three-part stress–strain curve. The first and last parts of the curve coincide with the stress–strain curves obtained by the limit Poisson’s ratio of 0.2 and 0.5, respectively, while a linear function serves as the transition curve in the middle region. The parameters of the middle zone were calculated using two different approaches: the first involved data fitting and optimization, while the second entailed using a proposed closed-form equation. The finite element program ABAQUS was employed to conduct incremental plastic analyses within the Concrete Damage Plasticity framework. The proposed model is capable of predicting the complete axial compressive stress–strain curve of concrete columns confined by AFRP and CFRP under monotonic compressive loading. A corroboration study was conducted using an experimental dataset from 24 concrete short column test specimens confined by AFRP and CFRP with a wide range of properties. The results showed that the average errors of both the proposed methods are nearly 3%. It means that both the numerical methods generally have a similar and acceptable precision.