Behavior of Steel Fiber-Reinforced Concrete Deep Beams with Large Opening

The authors report on very interesting tests that help readers better understand the merits and shortages of strut-and-tie models (STM). The design STM adopted in this study has one remarkable characteristic: the concrete part below the opening is not needed for the equilibrium of the deep beam. Nevertheless, a deep beam without an opening requires a continuous tie between the two supports, increasing the size of the opening a frame forms-at least a continuous tie is needed there, too. According to the load-displacement diagrams, Specimen RC2 displayed proper post-yield strain-hardening behavior. The authors claim that "it was due to the yielding of the bottom longitudinal reinforcing bars in tension." Nevertheless, Specimens SFRC 1 and SFRC2 had the same longitudinal reinforcement, but the load-displacement responses were quite dangerously brittle.