Behavior of two-way concrete slabs reinforced with fibers

The flat plate-column connection is a structural system, where columns without capitals or drop panels support the slab. This type of connection is governed by its weak strength of two-way shear (punching shear), which shows high brittleness behavior that leads to collapse. Adding the various types of fibers were the most important solution. Moreover, fibers are adding to the dense matrix in order to decrease the brittleness, in turns, increasing the sense of the matrix is increasing the bond with fibers and increasing the post-cracking strength. Fibers used in Reinforced Concrete (RC) that randomly oriented making the concrete behave as composite materials, which improve the residual strength of the members. Behaviors of the flat plate-column assembly of ten reinforced slabs were investigated.Synthetic fibers (Polypropylene and two aspect ratio ofpolyvinyl alcohol)were added to the dense concrete that includes 63% of fine aggregate. Ten square slabs ofsame reinforcement ratio (0.9%) and same dimensions (500 × 500 × 60 mm) were used in investigation.The main parameters was the effect of different fibers type and volume fraction of the fiber. Where, two types of fiber are used, with three percentages of volume fraction, fibers are used (0.5, 1.0, and 1.5%), compared to normal concrete slabs. The obtained result were compared with the proposed equation by ACI318-14, where the maximum ultimate load obtained from experimental work was higher than that ultimate punching shear load by 186%. This result was reached by adding 0.5% of PVA of 6 mm length.The test results shows that, adding fibers to the dense concrete are increased compressive strength by 74%, moreover, increasing the load resistance gradually as the fiber content increases.The enhancement of the ultimate resistance load can reach 45%.In the same manner, adding fiber, increased the first crack resistance load up to 59%, and reduced the deformation of the slabs compared to the normal concrete. Key Words:PVA and PP fibers reinforced concrete,residual punching shear strength, conventional steel reinforcement.