Structural synthesis has been denned as the rational directed evolution of a structural configuration, which in terms of a denned criterion, efficiently performs a set of specified functional purposes. An automated, minimum weight, optimum design capability for rectangular, simply supported waffle plates subjected to a multiplicity of inplane load conditions is presented. The synthesis involves six design parameters (total depth, back-up sheet thickness, stiffener thickness in the x and y directions, and stiffener spacing in the x and y directions). The behavior constraints are provided primarily by elastic stability failure modes. In particular, gross instability of the waffle plate, buckling of the back up sheet panel, and stiffener buckling are prevented in each of several load conditions while seeking a minimum weight design configuration. Side constraints in the form of upper and lower bounds on the design parameters due to external considerations (such as space limits and manufacturing capabilities) are provided. The mathematical programming problem to which this structural synthesis problem leads has the following characteristics: 1) relative minima; 2) nonlinear inequality constraints; 3) a multitude of side constraints; and 4) nonlinear merit function. Numerical results for several symmetric as well as unsymmetrical waffle-plate optimum designs are presented. The results of the waffle-plate synthesis study support the contention that structural synthesis capabilities for complex structural configurations of current and future importance are feasible. Amn a b bx by Ca DI Z>2