Region-based steel fiber placement in reinforced concrete beams under flexure: A critical review and mechanics-informed framework

Abstract

Steel fibers can improve crack control, post-cracking stiffness, ductility, and energy absorption of reinforced concrete beams; however, their efficient placement in critical load-resisting regions remains insufficiently clarified. This critical review synthesizes published evidence and structural-mechanics considerations to develop a mechanics-informed framework for region-based steel fiber placement under four-point bending. The beam is conceptually divided into a constant-moment region and two combined moment–shear regions. The reviewed evidence and mechanics-based interpretation suggest that fibers in the constant-moment region may primarily contribute to flexural crack control and post-cracking stiffness, whereas fibers in the combined moment–shear regions may contribute to restraining inclined cracking and influencing flexural–shear behavior. Fiber location, fiber content, and longitudinal reinforcement are identified as principal comparative variables, while fiber geometry, concrete properties, and testing conditions are treated as contextual factors. The framework further distinguishes equal-local-dosage and equal-total-fiber-mass comparisons to separate the influence of fiber location from total fiber consumption. It provides testable comparison principles for evaluating crack control, post-cracking response, failure behavior, and material efficiency. Experimental validation is required before the relative effectiveness of the proposed placement schemes can be established.