Optimizing Structural Response of Beams Strengthened with GFRP Plates

This paper addresses the structural implications when a glass fiber reinforced plastic (GFRP) plate is bonded externally to a reinforced concrete (RC) beam for flexural strengthening. Full-scale beams were tested in the laboratory to identify the differences in behavior of a GFRP-plated RC beam from that of a steel-plated one, and then special design techniques were developed to enhance the utilization of the GFRP plate material. The design technique that was adopted improves the ultimate load capacity of the strengthened composite beam and enhances its ductility in terms of deflection at midspan, energy absorption capacity, and curvature in the pure bending region. Preservation of the plate-adhesive-concrete interface bond and strengthening the compression concrete by confinement through the use of bonded plates onto the beam web are two critical features of this design approach. Experimental observations indicate that there is a limiting thickness to the compression plate beyond which premature bond failure may occur. An analytical model to predict the failure load of the strengthened composite beam is presented that shows good agreement with the test results and confirms that plates effectively bonded to confine the compression concrete make an effective contribution to the composite beam strength, stiffness, and ductility.