The paper describes an optimisation technique for the lightweight design of composite laminated beamswith a big ratio of span to thickness. The optimisation model for the lightweight design is to find the fibrevolume fractions to minimise the mass of the composite laminated beams under the eigenvalue (orfrequency) constraints. The analytical sensitivity of the eigenvalues, with respect to the fibre volumefractions, is formulated using the Euler–Bernoulli beam theory. The analytical formulae for sensitivityanalysis are suitable for the different boundary conditions (pinned–pinned, fixed–fixed, fixed–free andfixed–pinned). The eigenvalues are linearised using Taylor’s series so that optimisation model isconverted to a linear programming problem. The iterative computational procedure is proposed to solvethe optimisation model and eliminate the Taylor’s series approximation since the current design pointmaybe not near the optimum design. Finally, the lightweight designs of the composite laminated beamswith different boundary conditions are performed. The merits of the proposed method and lightweightdesigns obtained by proposed method are discussed.
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