Experimental and Numerical Assessment of Flexural Behavior of CFRP–Strengthened Timber Beams

Glued laminated timber (glulam) is increasingly adopted as a sustainable structural material; however, its performance under bending can be limited by brittle tensile failures and variability caused by natural defects. This study examines the flexural behavior of glulam beams strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets. A four-point bending experimental program was carried out on glulam beams with varying CFRP bonded lengths, including unreinforced control beams. The results demonstrate that CFRP reinforcement enhanced load-carrying capacity by up to 48%, increased stiffness, and shifted failure modes from brittle tension-side ruptures to more favorable compression-controlled mechanisms. A nonlinear finite element (FE) model was developed using DIANA software 10.5 to simulate the structural response of both unreinforced and CFRP-strengthened beams. The numerical model accurately reproduced the experimental load-deflection behavior, stress redistribution, and failure trends, with deviations in ultimate load prediction generally within ±16% across all reinforcement configurations. The simulations further revealed the critical influence of CFRP bonded length on stress transfer efficiency and failure mode transition, mimicking experimental observations. By integrating experimental findings with numerical simulations and simplified analytical predictions, the study demonstrates that reinforcement length and bond activation govern the effectiveness of CFRP strengthening. The proposed combined methodology provides a reliable framework for evaluating and designing CFRP strengthened glulam beams.