Damage evolution in reinforced concrete beams with low longitudinal steel ratio and steel or polypropylene fiber-reinforced concrete matrices under non-reversing cyclic loading

La Torre Esquivel D.; Marques Rodrigues Gaspar C.; Almeida Del Savio A.; Puchuri Mayuri S.; de Andrade Silva F. · Construction and Building Materials (2026) · DOI: 10.1016/j.conbuildmat.2026.147907

Resumen

Fiber-reinforced concrete (FRC) matrices can improve crack control and post-cracking performance in reinforced concrete members; however the combined effects of fiber type, effective span, and non-reversing cyclic loading on damage evolution in beams with low longitudinal steel ratios remain insufficiently understood. This study evaluates 18 simply supported reinforced concrete beams with a low longitudinal steel ratio of 0.31% and reference, 1.0% polypropylene-fiber, or 1.0% steel-fiber concrete matrices subjected to monotonic and non-reversing cyclic loading. The experimental program considered total beam lengths of 1.6 and 3.2 m, corresponding to effective spans of 1.5 and 3.0 m, and assessed load–displacement response, cracking, stiffness degradation, reinforcement strains, hysteretic energy dissipation, and variations in dynamic properties. Operational Modal Analysis (OMA) of ambient-vibration responses was performed at selected damage states, and bending-mode natural frequencies were identified using Enhanced Frequency Domain Decomposition. Relative to conventional RC, the mean yield load increased by 14% with polypropylene fibers and by 35% with steel fibers. Steel fibers provided the greatest initial and post-cracking stiffness, but also produced stronger post-yield localization in one dominant crack and reduced deformation capacity, particularly in the longer beams. Peak hysteretic energy dissipation was span-dependent: in the shorter beams, the values were 19.0, 26.5, and 29.1 N·m for RC, RC-PPRC, and RC-SFRC, respectively, whereas in the longer beams the ranking changed to 17.0, 20.7, and 14.8 N·m. The first bending-mode frequency loss, defined as the percentage reduction from the undamaged natural frequency immediately after cracking, was 19%, 15%, and 8% in the shorter RC, RC-PPRC, and RC-SFRC beams, respectively, and 13%, 7%, and 7% in the corresponding longer beams. Natural frequency was more sensitive and reliable than modal damping for tracking damage. These results show that steel fibers favor strength and stiffness but require verification of post-yield localization, whereas polypropylene fibers favor a more distributed deformation response and higher energy dissipation in longer beams. Combining mechanical response parameters with OMA-based frequency indicators provides a more complete assessment of damage evolution.

Instituciones: Universidad de Lima