Shear Behavior of Steel Fiber Reinforced Concrete Beams without Stirrup Reinforcement.

Abstract

This research aims to study: (1) the behavior and ultimate shear strength of steel fiber reinforced concrete (SFRC) beams; (2) the possibility of using steel fibers as minimum shear reinforcement in reinforced concrete (RC) beams; and (3) the effectiveness of steel fibers as a means to reduce shear size effect in RC beams. A total of 28 simply-supported beams with a shear span-to-depth ratio of 3.5 were subjected to monotonically-increased, concentrated load. Target concrete compressive strength for all beams was 6000 psi. The studied parameters included fiber type, fiber volume fraction (between 0.75 and 1.5%), longitudinal tension reinforcement ratio (approximately 1.6, 2.0 and 2.7%), and beam depth (18 in. or 27 in.). Three types of steel fibers were considered, all with hooks at their ends. Two of the fibers evaluated were 1.2 inch long, with aspect ratio of either 55 or 80. The third type of fiber investigated was 2.36 inch long, with an aspect ratio of 80. Test results showed that the use of hooked steel fibers in a volume fraction greater than or equal to 0.75% led to a substantial increase in shear strength and significantly reduced the size effect for shear strength of beams with depths of up to 27 in. The results also indicated that hook steel fibers can be used as minimum shear reinforcement in RC beams constructed with normal-strength concrete and within the depth range considered. A method to predict the shear strength of SFRC beams based on a Pister and Bresler concrete failure criterion and on the average tensile strength of the SFRC obtained from a standard ASTM four-point bending test was proposed. The method proved to provide reasonable predictions of shear strengths for the SFRC beams tested in this experimental program, as well as in previous research reported in the literature. An average tensile strength for the SFRC as a function of fiber volume fraction and aspect ratio was also recommended for the purpose of shear design of SFRC beams.