ABSTRACT
This study presents a 2-D numerical framework to simulate the behavior of reinforced concrete (RC) beams, both unstrengthened and externally strengthened with fiber-reinforced polymer (FRP). The approach is based on an alternative Finite Element Method (FEM) that uses positions instead of displacements as primary unknowns, allowing for a natural treatment of geometric nonlinearity. The Mesh Fragmentation Technique (MFT) is adopted to capture the nonlinear behavior of concrete by inserting High Aspect Ratio (HAR) solid elements between bulk elements. Crack initiation and propagation are modeled through a continuous damage model applied only to the HAR elements, keeping the bulk elements linear elastic.A position-based HAR interface element is also introduced to model the interaction between concrete and reinforcements. A J2 continuous damage model describes the bond-slip behavior and degradation between concrete, steel bars, and external FRP sheets or plates. The main contributions include the integration of the MFT with HAR interface elements to represent both crack growth and bond deterioration, combined with the extension of these concepts to a position-based FEM for general nonlinear analyses. The results confirm that the proposed framework accurately reproduces the response of RC beams and captures FRP debonding due to intermediate crack formation.
