Decomposition of the Shear Capacity of Steel Fiber–Reinforced Concrete Coupling Beams

Steel fiber–reinforced concrete (SFRC) is extensively used in coupling beams due to its superior mechanical properties. In this study, the two-parameter kinematic theory is modified by introducing the consideration of the critical crack angle and longitudinal reinforcement strain. The modified method is validated by 64 sets of experimental coupling beams in the literatures, and the predicted shear capacities are found to have good agreement with the test results. Moreover, the decomposition of the shear capacity provided by steel fibers, stirrups, the critical loading zone, aggregate interlock, and the dowel action of the longitudinal reinforcement can be evaluated separately. Thus, the effects of the span-to-depth ratio, volume fractions of fibers, and stirrup ratios on the shear capacity are investigated. Additionally, the equivalent substitution relationship between stirrups and steel fibers is quantified, which provides a solution to the reduction of the density of stirrups in coupling beams and similar components.