Punching shear behavior of RC slabs incorporating macro-synthetic fibers

The effect of macro synthetic fibers on punching shear behavior of reinforced concrete slabs was investigated. Twenty-four square reinforced concrete slabs (1500 mm x 1500 mm) were pre -pared, instrumented, and tested under monotonic, displacement controlled, center-point load in a simply-supported configuration. The main test parameters were the fiber volume fraction (0.5% and 1%), slab thickness (100 mm and 150 mm), and the flexural reinforcement ratio (0.9% and 1.5%). Test measurements included applied load, slab deflection, strains in the steel reinforce-ment and in the concrete. The development of the cracks for the duration of the test was also monitored and recorded. The test results showed that the punching shear strength, deflection capacity, and energy absorption of the FRC slabs were significantly improved by the presence of macro synthetic fibers. This improvement was associated by a more defined punching shear area, higher cracking density, higher strain in the concrete and a lower strain in the reinforcement steel. Furthermore, the level of improvement was found to be more pronounced in the FRC slabs with lower thickness, lower reinforcement ratio and higher fiber volume fraction.