This study developed a higher order shear deformation theory and fourth order displacement
polynomial in the static flexure analysis of thick isotropic plate under uniformly distributed load.
Total potential energy equation of a thick plate was formulated from the constitutive relations
thereafter the three governing differential equation and boundary conditions of the theory are
obtained by the method of direct variation to the determination of the out of plane
displacement and shear deformations rotation along the direction of x and y coordinates were
obtained. These equations as obtained are solved simultaneously after minimization to
determine the coefficients of deflection and shear deformations along x and y axis. From the
formulated expression, the formula for calculation of the actual in-plane and out-of-plane
displacements, moment and stress in the plate is determined. A numerical solution of thick
rectangular plate clamped on adjacent near edges, free and simply supported on adjacent far
edges (CCFS) was computed for various aspect ratios of the plate. The result shows that the
values of the deflection, bending moment and stress decrease as the span to thickness ratio
increases. These decreases continue until failure occurs in the plate structure. This means
that, the load that causes the plate to deflect also causes the plate material to bend
simultaneously. It is observed that the value of deflection varies less as the span to thickness
increase, this equal to the value of the CPT at span to thickness ratio of 90 and above. The
results obtained are compared with an available solution in the literature showed good
agreement with those in the literature.