Effective Critical Section Evaluation of a Reinforced Concrete Flat-Plate Slab with Openings for its Punching Shear Strength Estimation

Most of current concrete design codes require that critical sections should be reduced in the presence of openings near columns to consider their effects on the punching shear strength of reinforced concrete flat-plate slabs. For example, ACI 318-11 stipulates that a part of the perimeter enclosed by two projection lines from the centroid of the column to the boundaries of the openings shall be considered ineffective. However, the direct application of this rule to practical cases may be rather complicated depending on the geometrical layout and shape of columns and openings. In this paper, simple mathematical formulations are proposed to evaluate the ineffective part of critical sections due to openings. This approach can be applied to the design of reinforced concrete flat-plate slabs based on ACI 318-11. A numerical algorithm is also developed to handle general cases where the ineffective parts of multiple openings overlap with each other.