Plates are flat structural elements with thicknesses much smaller than the other dimensions. Familiar examples of plates include flat roofs, doors, table tops, and manhole covers.
In analyzing a plate (Fig. 13.1), it is common to consider the plate to be divided into equal halves by a plane, the midplane or middle surface, parallel to the flat faces. The plate thickness t is measured normal to the middle surface. The fundamental equations of plate theory relate the displacements and forces of the middle surface to the applied loading. Plate equations will appear similar to beam equations, since beam theory can be regarded as a special case of plate theory.