# Punching Shear Strength of Reinforced Concrete Flat Plates with GFRP Vertical Grids
## 1 Introduction  
A flat plate is a structural element composed of slabs and columns without beams. Owing to the weight of the flat plate that is directly delivered to a column from a slab, a large stress concentration develops around the column causing a punching shear failure. This brittle punching failure is prompted by large shear forces and unbalanced moments transferred from the slab-column joint due to the severe horizontal displacement associated with seismic loads. Shear reinforcement is necessary to mitigate and prevent the brittle failure due to punching shear. As one of the effective shear reinforcements, the method employing a fiber reinforced polymer (FRP) has received the most attention due to the benefits of FRP such as it being lightweight with a high tensile strength and its ability to be manufactured in various shapes. FRP sheets, strips, laminates and rods have been extensively applied for the reinforcing and strengthening of reinforced concrete structures [1, 2, 3, 4]. [PERSON] et al. [5] evaluated the punching shear performance of a flat plate by manufacturing a glass fiber reinforced polymer (GFRP) bar and used the manufactured GFRP bar instead of a steel tension reinforcement for the flat plate. [PERSON] et al. [6] investigated the punching shear of two-way concrete slabs with a GFRP bar as a flexural reinforcement and stirrups. They conducted the tests on 10 full-scale interior slab-column specimens considering the flexural reinforcement ratio and shear reinforcement ratio and type. The test results indicated that the punching shear capacity was governed by the flexural reinforcement ratio but the performance was enhanced by reducing the brittleness when FRP stirrups were used. Many studies have been conducted on flat slab strengthening with FRP composites. [PERSON] et al. [7] experimentally verified that shear strength increased when using reinforcing carbon fiber reinforced polymer (CFRP) produced in the shape of a rod by drilling a hole in the critical section of the flat plate. [PERSON] et al. [8] reinforced the CFRP by manufacturing it as a strip and attaching it to the underside of the flat plate; they experimentally assessed the performance of the flat plate and the applicability of theequations of the Canadian Standards Association (CSA) and the American Concrete Institute (ACI). [PERSON] and [PERSON] [9] proposed a numerical model to predict the behavior of the strengthening of flat slabs with externally bonded FRP strips. [PERSON] et al. [10; 11] evaluated the numerical approaches to predict the structural behavior and seismic fragility for the floor of an existing reinforced concrete (RC) building. As a result of performing a modal linear analysis, the comparison showed a substantial equivalence between the model using the rigid floor assumption and an equivalent shell.  
Design standards provide the punching shear strength of concrete flat plates shear reinforced with steel stirrups with the shear strength equation of the flat plates shear reinforced with FRPs. In this study, the amount and the spacing of the shear reinforcement were examined by performing a punching shear experiment on the flat plates. The shear strengths of the flat plates were calculated from the shear strength equations of ACI 318-19 [12], BS 8110 [13] and Eurocode 2 [14]. Their applicability was assessed by comparing them to the experimental results.