Flexural Behavior of Steel Fibrous Reinforced Concrete Deep Beams

Abstract

Experimental research was carried out regarding the flexural behavior of deep beams cast with plain and fibrous concrete with hooked steel fibers, and subjected to monotonic vertical loads. Four deep fiber-reinforced concrete beams were cast. Two of them were made of plain concrete with main and web steel reinforcements (RC), and two were made of hooked steel fiber-reinforced concrete (SFRC) with main steel reinforcements. The experimental results show the brittle behavior of reinforced deep RC members characterized by crushing of concrete struts and fracture of web steel bars. SFRC deep beams exhibit higher strength and, above all, ductility with respect to RC members due to the bridging actions of fibers across main and secondary cracks. From the analytical point of view, a softened strut-and-tie macromodel able to reproduce the flexural behavior (in terms of multilinear load-deflection curves) of deep beams in plain and fibrous concrete and with the presence of horizontal steel bars, including softening of compressed struts and yielding of steel bars, is presented. The model is able to take into account the tensile behavior of main bars embedded in the surrounding concrete and the softening of the compressed strut, the arrangement and percentage of the steel bars, and the percentage and aspect ratio of steel fibers. The experimental results obtained here and those available in the literature are compared with the results obtained through the proposed model and with the other models given in the literature, showing good agreement. Finally, a validation of the proposed model is made numerically by using a nonlinear finite-element program (ATENA-2D) able to analyze the flexural behavior of deep members.