Shear Strength of Extruded, Prestressed Steel Fiber- Reinforced Concrete Hollow-Core Slabs

ACI 318-19 requires that prestressed concrete hollow-core slabs with depths exceeding 12.5 in. (320 mm) and subjected to a factored shear greater than half the design web-cracking shear strength be provided with at least minimum shear reinforcement. Because the use of bar-type shear reinforcement in hollow-core slabs is generally not possible, this requirement limits the use of these members in shear-critical cases. In this research, the use of hooked steel fibers as a means to increase the shear strength of deep hollow core slabs was evaluated through 14 tests on extruded hollow-core slabs. Slab thickness was 16 in. (406 mm) and the shear span -effective depth ratio (a/d) was either 3.0 or 3.5. Two types of hooked steel fibers were evaluated at dosages between 40 and 62 lb/yd3 (24 and 37 kg/m3). Type 1 fibers had a single hook at each end and Type 2 fibers had double hooks at each end. The fiber-reinforced concrete slabs exhibited peak shear strengths that ranged between 0.94 and 1.29 times the ACI 318-19 calculated web-cracking shear strength Vcw, while the two slabs without fibers failed at shear forces corresponding to 0.93 and 0.87Vcw. Besides an increase in shear strength, the presence of fibers, particularly Type 2 fibers, led to a more gradual post-peak strength decay. Failure of the hollow core slabs without fibers occurred as soon as one web exhibited web-shear cracking. In the hollow-core slabs with fibers, on the other hand, fibers bridging the first web-shear crack prevented this web from experiencing a sudden loss of shear capacity, which allowed the slabs to sustain additional shear until multiple webs had cracked in shear.