Flat slab system is commonly used because of aesthetic appearance and flexibility of architecture. The punching shear is the major drawback of this structural system. The punching shear causes sudden failure lead to total collapse in the structure. In this paper 3D models that follow the method of applied element (AEM) to analyze the behavior of interior column-slab connections exposed to vertical displacement. The aim of this paper to show the importance of providing various types of punching shear reinforcement in the connection and improve the capacity of column-slab connection to prevent the local failure. The numerical study involved twenty six full-scale interior column- slab connections. This study is divided into two groups in addition to a control model where this model has no punching shear strengthening. The first group has thirteen models with additional punching strengthening such as closed stirrups around the column. The second group contains thirteen models with additional punching strengthening such as multi leg stirrups. The ultimate load is compared among several models. The simulated results display that shear strengthening improve both of strength.