Effects of openings on the punching shear strength of reinforced concrete slabs

In recent years, the application of reinforced concrete (RC) flat slabs has dramatically increased due to their functional and economic advantages. The exhibition of higher stress at the slab-column connections causes failure, and the punching shear is most likely the governing failure mode for these structures. Besides, the existence of opening positioned close to the column intensifies the vulnerability to punching shear failure of slabs. The current research aims to study the behavior of RC slab-column connections under vertical loads as well as to investigate the effects of openings on the punching shear strength of RC slabs. For this purpose, the finite element (FE) modeling is used to investigate the effects of openings varying in size and location on the punching shear stress of the connections. In the first step, an FE model is developed and validated by an experimental specimen of a slab-column connection from available research. In the second stage of the study, 8 interior connections and 8 edge connections are analyzed under incremental vertical load. Each connection has one opening with the dimensions of 150 x 150 mm and 250 x 250 mm located 0, 75, 150, and 300 mm far from the column in a parallel position while a connection without opening is considered in each case as a reference. Numerical results demonstrate that near-column openings cause a remarkable increase in the shear stress around the slab-column connections. Furthermore, a significant increase in shear stress around the openings is observed by increasing the dimensions of the opening and reducing the distance of opening from the column.