In some applications of thin plates, the maximum deflection is equal to or larger than the plate thickness. Because of these large displacements, the midplane stretches and hence the in-plane tensile stresses develop within the plate, causing the plate to stiffen and adding considerable load resistance, which are not predicted by the small-deflection bending theory. For such situations, an extended plate theory is used in this chapter, accounting for the effects of large deflections. The large-deflection theory of plates assumes that the deflections are no longer small compared to the thickness, but are nevertheless small relative to the other plate dimensions.

First, large-displacement behavior for plates of simple form is illustrated, primarily to give some idea of the additional load-carrying action. The behavior described is also generally valid for plates of any other shape. This is followed by a discussion demonstrating the differences between the small- and large-deflection theories. Next, the general analytical solution of plate problems is formulated. Then, the application of the energy method to the solution of problems involving large plate deflections is treated. The final section presents the finite element solution for the bending of plates experiencing large deflections.