Experimental Study of Punching Shear Resistance of Synthetic Fiber Reinforced Concrete Interior Slabs

Abstract

This study experimentally explores the suitability of Synthetic Fiber-Reinforced Concrete (SNFRC) as a feasible method for improving the punching shear strength of two-way slabs. The investigation involved interior flat slab panels made with two synthetic fiber volumetric percentages, as well as three spacing configurations for the flexural reinforcement. Nine full-scale, 2m*2m*0.15m slabs, are utilized to quantify the SNFRC impact on punching shear strength, toughness and deformation capacity. The nine slabs are divided into three groups of fiber volumetric content: 1.25%, 0.75% and 0%. Each group consists of three flexural steel reinforcement spacing configurations: 16mm-diameter rebars at 60mm, 80mm and 110mm. For SNFRC material characterization, compressive strength and tensile rupture strength are captured via standard 150*150*150mm cubes and 150*150*500mm rectangular prisms, respectively. Material characterization revealed that the introduction of synthetic fibers had a negligible impact on the compressive strength. A reduction of merely 3.4% and 2.3% is associated with adding 1.25% and 0.75% fiber content, respectively. Conversely, the three-point loading test results in 14% and 4% higher rupture tensile strengths associated with 1.25% and 0.75% fiber contents. Moreover, the introduction of synthetic fiber dosages of 1.25% and 0.75% resulted in considerable improvement to the punching shear strength, 36% and 15%, respectively. The greatest effect of the synthetic fiber is found to be on the slab deformation capacity and toughness (quantified as the area under the load-deflection curve). For the 0.75% fibers group, the improvement ranged from 67% to 274% associated with the 60mm the 110mm spacing, respectively. Similarly, for the 1.25% group, the corresponding counterparts have an improvement range of 82% to 324%. For comparison purposes, several analytical predictions for the punching shear strength are made in accordance to the CEB-FIB 2010 Model Code, ACI-318, ACI-544 codes as well as models available in the literature. One particular model is found to best agree with SNFRC slabs when it is re-calibrated in this study. The re-calibration utilized the differences in the steel and synthetic fibers mechanical properties. Namely, Young's modulus, the tensile strength and fiber-concrete bond strength.