Numerical Investigation of the Structural Behavior of Ferrocement-Strengthened Reinforced Concrete Beams with Shear-Zone Openings

Abstract

The presence of openings in reinforced concrete (RC) beams significantly compromises their structural performance by inducing stress concentrations at opening corners, reducing stiffness, and increasing deformation. This study investigates the effectiveness of ferrocement — a thin cement mortar layer reinforced with a welded wire mesh — as a strengthening technique for RC beams containing square openings located in the shear zone. A nonlinear finite element model was developed using the ABAQUS program, employing the Concrete Damaged Plasticity (CDP) constitutive model for concrete and standard truss elements for steel reinforcement. The numerical model was validated against published experimental data, achieving 92% agreement in mid-span deflection at the ultimate load level. Following validation, six RC beam specimens with square openings of three different sizes relative to beam height — 0.25H, 0.5H, and 0.75H — were analyzed in both unstrengthened and ferrocement-strengthened configurations, alongside one solid reference beam with no openings, giving seven beams in total. Results demonstrate that ferrocement strengthening substantially improved structural performance across all opening sizes. For beams with 0.25H and 0.5H openings, mid-span deflection under a 150 kN applied load was reduced by approximately 64% and 62%, respectively, compared to the unstrengthened reference beam. For the largest opening (0.75H), where the unstrengthened beam sustained only 10 kN before failure, the ferrocement layer restored full load-bearing capacity to 150 kN, reducing deflection by 14% relative to the solid reference beam. Furthermore, maximum shear stress in all ferrocement-strengthened beams approached or exceeded that of the solid reference beam, confirming the effectiveness of the strengthening layer in restoring shear resistance lost due to the presence of openings.