Cyclic flexural performance of RC beams with small circular openings in plastic hinge region

Abstract

This paper describes the effect of a small circular web opening located in the plastic hinge region on the cyclic flexural performance of RC beams. The variable in the design of specimens is the diameter of the circular web openings installed in the plastic hinge region. Two rectangular beams scaled down to 67% of a practical RC beam were fabricated to have circular openings in the plastic hinge region with diameters 0.2 and 0.3 times the height of the beam. In another beam, in addition to the opening in the plastic hinge region, a web opening with a diameter of 0.3 times the height of the beam was installed at a location 180 mm from the center of the span. A total of four beams including a control beam were subjected to cyclic anti-symmetric moment. The cyclic flexural performance of the beams was evaluated in terms of hysteretic response, including strength, stiffness, ductility, and energy dissipation capacity. The neutral axis depth of the plastic hinge during the cyclic loading test was calculated using the linear distribution of strains of longitudinal reinforcing bars placed at the top and bottom of the openings. In addition, using the effective depth of the RC beams and the net tensile strain in the extreme tension reinforcement for tension-controlled sections, which are recommended by ACI 318–19, the maximum diameter of the circular web opening in the plastic hinge region was approximated and compared with the test results. Furthermore, with reference to the results of certain exiting studies, the ratio of the spacing between openings to the maximum diameter of the circular web opening was suggested by assuming the case of designing web openings to leap over major shear cracks expected to occur in a flexural RC beam undergoing shear-flexural failure.