Influência da adição de fibras no comportamento ao cisalhamento de vigas de concreto de alta resistência

Abstract

The understanding of shear behavior in reinforced concrete beams is a relevant topic in structural engineering, especially with the introduction of fibers into the cementitious matrix, which increases the complexity of the resisting mechanisms but provides gains in ductility, residual strength, and crack control. Research has focused on conventional-strength concretes, leaving gaps regarding the performance of high-strength concretes (C55–C90) with diverse types and dosages of fibers and their behavior in beams without transverse reinforcement. This study investigated the contribution of fibers to the shear resistance of high-strength fiber-reinforced concrete (HSFRC) beams without stirrups and conducted a critical assessment of the applicability of the design equations of ABNT NBR 16935 (2021) for estimating the shear capacity of these beams, which are currently not addressed by the standard. The results were compared with recent international guidelines from Eurocode 2 (2023) (EC2) and the fib Model Code 2020 (2024) (MC2020). The experimental program included the mechanical characterization of C55, C70, and C90 concrete reinforced with steel fibers and macro-synthetic fibers (0.5% and 1.0%), comprising compressive strength, elastic modulus, residual flexural tensile strength, and direct shear strength tests using the JSCE-SF6 and push-off methods. HSFRC beams without transverse reinforcement were evaluated to evaluate the influence of concrete strength, fiber type, and fiber dosage on shear behavior. Digital image correlation (DIC) was employed in selected tests to analyze the cracking process. The results showed that fiber addition increased the cracking load, controlled crack opening, and enhanced shear resistance, particularly in the case of steel fibers. The direct shear test methods exhibited significant variability in their results, indicating the need for standardization. The analysis revealed that ABNT NBR 16935 (2021) tends to overestimate the shear capacity of HSFRC beams, whereas the EC2 and MC2020 formulations proved to be more conservative. A calibration of the EC2 equations was proposed, resulting in improved agreement with the experimental results and reduced dispersion. These findings provide a relevant contribution to Brazilian standardization, aligned with experimental evidence and international trends, enabling the safe and economical use of fiber-reinforced concrete in structural elements.