Experimental Study on Crack Bridging in FRC under Uniaxial Fatigue Tension

This paper presents an experimental study on crack bridging in steel-fiber-reinforced concrete (SFRC) materials under deformation-controlled uniaxial fatigue tension. Two types of commercially available steel fibers, straight steel fiber and hooked end steel fiber, were used separately in this experimental investigation. A total of six series of fatigue tensile tests with constant amplitude between maximum and minimum crack openings were conducted. The experimental results show that the bridging stress decreases with the number of load cycles, and this phenomenon is termed bridging degradation. The general behavior of the bridging degradation with the number of cycles in SFRCs is represented by a fast dropping stage (reduction in bridging stress within the first 10–15 cycles) with a decelerated degradation rate, followed by a stable stage with an almost constant degradation rate for straight SFRC, or by several periods with a decelerated rate in each period for hooked SFRC. Although fiber deformation, such as in hooked end fiber, can improve the monotonic crack bridging significantly, faster bridging degradation is found in hooked SFRC than in straight SFRC with the same maximum crack width (>0.1 mm) and minimum load condition.