Flexural resistance mechanisms in reinforced concrete have been well documented for over a century. However, distributed quantification of these mechanisms, such as tension softening, tension stiffening, and other forces at and between cracks, to our best knowledge, previously has not been possible. Distributed fiber optic sensors (DFOS), which can provide strain measurements at submillimeter sensor spacings, now make it possible to quantify these forces. This paper presents results from lightly reinforced, moderately reinforced, and horizontally functionally graded reinforced concrete slab strips instrumented with DFOS on the longitudinal reinforcement and the concrete surface and tested in four-point bending. DFOS on the surface of the concrete allowed the estimation of distributed concrete compressive forces and tension stiffening behavior, while DFOS on the steel reinforcement allowed the determination of the force in the steel. Moment and force equilibrium allowed the calculation of tension stiffening and tension softening forces. Results indicate the need for localized vertical forces in the constant moment region of lightly reinforced slab strips in order to maintain equilibrium, which implies the current understanding of the behavior of reinforced concrete tension stiffening behavior may be incomplete.
Yager et al. (Fri,) studied this question.