Optimal Shape and Size of Holes in Hybrid Reinforced Concrete Beams

Abstract

Hybrid reinforced concrete structures are efficient systems that include steel and fiber-reinforced polymer (FRP) reinforcement advantages, which are called fiber steel reinforced concrete (FSRC). On the other hand, passing service pipes through creating holes in reinforced concrete (RC) beams completely changes their structural behavior. Besides, RC beams with holes require rigorous nonlinear finite element (NLFE) analysis which is not typically done by design engineers. The behavior of simply-supported FSRC beams (hybrid reinforced with basalt FRP (BFRP) and steel bars) having two end holes under the effect of four-point bending loading tests was investigated. Also, NLFE models were developed, verified, and implemented in an extensive parametric study. The studied parameters related to (1) hole shapes: circular, square, and rectangular shapes; (2) height/or diameter: ho=0.2h, 0.3h, 0.4h, and 0.5h; and length: Lo=0.3h, 0.5h, 0.7h, and 1.0h. Compared to a similar beam without holes, the holes produce reductions of up to 53%, 44%, 85%, 64%, and 58% in the beam’s cracking load, ultimate strength, absorbed energy, post-cracking stiffness, and post-yield stiffness, respectively (the lowest in cases of circular holes). It was noted that hybrid reinforcement significantly affects the behavior of beams with holes. In order to obtain the benefit of this behavior, it is recommended to drill the beam with a hole size diameter of up to 0.4h and up to a hole size length of 0.3h for square holes. On the contrary, the effect of hybrid reinforcement gains less significant enhancement in the case of the rectangular holes.