Practical Estimation of Two-Way Slab Deflections

The calculation of the deflection of a reinforced concrete element is usually troublesome, and is even more problematic for two-way slabs than for beams. An algebraic equation was developed in this paper for estimating the midpanel deflections of the two-way slab systems subjected to uniform gravity loads. The proposed method was initially derived from the differential equation of plate and then calibrated using the results of finite-element analyses to estimate the elastic deflections of interior panels. The proposed procedure was further directed toward the general problem concerning progressive cracking of concrete, varied boundary conditions due to discontinuity of slab, and long-term effects. The resulting expression provides a more accurate representation of the midpanel deflection than does the simpler method outlined in the ACI Committee 435 report. The adequacy of the proposed procedure was checked by comparing calculated deflections with experimental data reported in previous literature, and satisfactory correlation was found. Finally, this paper includes numerical examples to illustrate use of the proposed equations.