The parametric eigenvalue problem in infinite-dimensional Hilbert space arising in the mechanics of loaded thin-walled structures is investigated. Asymptotic properties of solutions depending on loading parameters are established. The initial infinite-dimensional problem is approximated in a finitedimensional subspace. Theoretical error estimates of approximate solutions are obtained. Effective numerical methods for calculating the main resonance frequency and the corresponding resonance form of vibrations based on asymptotic formulas are proposed.