Use of steel fibers as transverse reinforcement in diagonally reinforced coupling beams with normal- and high-strength concrete

This study investigates the effects of using steel fibers as transverse reinforcement on the seismic performance of diagonally reinforced coupling beams that are composed of normal- and high-strength concrete. Four types of coupling beams were fabricated and tested under quasi-static reversed cyclic loading. A normal-strength reinforced concrete (RC) coupling beam with the compressive strength of 40 MPa was designed with the full confinement of a beam section according to ACI 318-14. A second RC coupling beam specimen with the same reinforcement details and concrete with the compressive strength of 80 MPa was fabricated also to evaluate the effects of strength. In addition, steel fiber was used in an attempt to simplify the complex details of transverse reinforcements for diagonally RC coupling beams. To this end, two fiber volume fractions of 1.0% and 1.25% were used for 40 MPa and 80 MPa steel fiber-reinforced concrete (SFRC) coupling beams, respectively. Test results indicated that the shear strength of the coupling beams increased with an increase in compressive strength, whereas the energy dissipation capacity was similar for the normal- and high-strength concrete RC coupling beams. Furthermore, this study found that the inclusion of steel fiber prevented buckling of the diagonal steel rebar as well as provided additional transverse reinforcement. The overall performance, including strength, stiffness degradation, and the energy dissipation capacity, of the SFRC coupling beams was similar to that of the conventional concrete coupling beams. Comparisons of the conventional concrete and SFRC beam specimens indicate that the use of steel fiber allows for the simplification of transverse reinforcement construction details for diagonally reinforced coupling beams.