Shear capacity of UHPFRC deep beams with web openings

Abstract

The shear capacity of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) deep beams with web openings located between the provided stirrups was investigated experimentally. All the tested beams were constructed from the same UHPFRC mix containing steel fibers volume fraction of 1.5 %. The test program included eight simply supported deep beams with the same cross-section and same longitudinal reinforcement. The principal studied parameters were opening height, width, location, and the stirrups ratio ρv %. The provided stirrups spacing sv was considerably more than the maximum stirrups spacing sv,max required by ACI 318 code for normal reinforced concrete, while sv,max required by the Egyptian code (ECP 203) were more or equal to sv. The equations used by French recommendations (AFGC) and Korea Concrete Institute (KCI) for the shear design of UHPFRC deep beams have been examined. The experimental results indicated that the shear capacity of UHPFRC deep beams is mainly controlled by opening height, width, and location. Square opening with a height of 20 % of the beam's overall height located at the natural load pass caused reduction of shear capacity by 43 % compared with the reference solid beam. Increasing the opening width by 75 % symmetrically around the natural load pass reduced the shear capacity of the UHPFRC beam by about 21 % while increasing the opening width by 125 % from one side out of the load pass caused a reduction by only 5 %. Increasing the stirrups ratio by 80 % for beams of similar opening size and location, increased the shear capacity by 17.1 %. Predicting the ultimate shear strength of the tested UHPFRC deep beams with openings of height 20 % and 40 % of the beam's total height using the equations of AFGC was just safe if these equations were calculated by deducting the height of opening from the beam effective depth. The equations used by KCI were also safe with a factor of safety about 6 % more than that of AFGC.