equality constraint was imposed on the modal damping
parameter and the inequality constraints on the cross-sectional
area of the members. In one design, the modal damping
parameter was specified to have the same value as that of the
nominal design and for the other it was increased by nearly a
factor of six over that of the nominal design. The distribution
of structural frequencies was different for the optimized structures.
The optimum design satisfied the equality constraints exactly.
In this investigation, the optimization procedure invokes
equality constraints on the closed-loop modal damping ratios
without specifying the modal frequencies. In a recent investigation
by the authors,14 the number of equality constraints were
increased to include the modal frequencies in order to exclude
the significant variation of the fundamental frequency during
the optimization process. Also, the optimized designs showed
considerable improvement over the nominal design in their
dynamic response.