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

Jarallah, Hazem Mohamed Shaif
A Master of Science thesis in Civil Engineering by Hazem Mohamed Shaif Jarallah entitled, "Experimental Study of Punching Shear Resistance of Synthetic Fiber Reinforced Concrete Interior Slabs," submitted in September 2016. Thesis advisor is Dr. Mohammad AlHamaydeh. Soft and hard copy available.
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.
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