Performance Evaluation of Carbon Fiber-Reinforced Polymer (CFRP) Sheets in the Seismic Retrofit of Reinforced Concrete Beam–Column Joints: A Comparison of Different Fiber Configurations and Orientations

Abstract

This study was conducted to comparatively evaluate the seismic performance of reinforced concrete beam–column joints strengthened with Carbon Fiber-Reinforced Polymer (CFRP) sheets, with a particular focus on the effects of fiber configuration and orientation. To achieve this objective, nonlinear analyses were carried out using the Finite Element Method (FEM) in ABAQUS software. Two principal CFRP configurations, namely cross-ply and unidirectional layouts, along with three different fiber orientations (0°, 90°, and ±45°), were investigated. The numerical models were first validated through comparison with reliable experimental data. The results revealed that the cross-ply CFRP configuration with ±45° fiber orientation was the most effective strengthening scheme, increasing the ultimate load-carrying capacity of the joint by up to 38% compared with the unstrengthened specimen, while also providing a significant improvement in ductility. In contrast, the unidirectional ±45° configuration achieved a 28% increase in strength and was identified as an optimal solution from a practical and implementation-oriented perspective for projects with operational constraints. The findings indicate that the seismic performance of beam–column joints is highly sensitive to both the configuration and, more importantly, the orientation of CFRP fibers. This study provides a scientific basis for the informed selection of strengthening strategies and offers a framework for the development of technical guidelines aimed at the safe and cost-effective seismic retrofit of vulnerable structural joints in earthquake-prone regions.