The purpose of this paper is to develop a lightweight designmethod for the composite laminated beams with a big ratio of span to thickness. The analytical sensitivity of the eigenvalues, with respect to the fibre volume fractions, is derived based on the Euler–Bernoulli beam theory. For the given fibre orientations and thickness of layers, the lightweight design optimisation model is to minimise the mass of the composite laminated beams so that the eigenvalue (or frequency) and fibre volume fraction constraints are satisfied. The eigenvalues are linearised using Taylor’s series and the lightweight design optimisation model is converted to a linear programming problem. The iterative algorithm is proposed to eliminate the Taylor’s series approximation since the current design point maybe not near the optimum design. Finally, the lightweight designs of the composite laminated beams with different boundary conditions and two given fibre orientations are demonstrated. The merits of the proposed method are also discussed.
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