CALCULATION AND MEASUREMENT OFnNORMAL MODES OF VIBRATION OF AN ALUMINUM-ALLOY BOXnBEAM WITH AND WITHOUT LARGE DISCONTINUITIES

摘要

The lowest normal modes of vibration of three aluminum-alloy box beams were calculated using a matrix iteration method. For these calcu¬lations the actual structures were idealized to a system of mass points interconnected by massless springs. The lowest normal modes of these beams were measured experimentally and compared with those calculated. This comparison indicates that the mode shapes and natural frequencies for structures of this type may be adequately calculated using this method. The experimental measurements were limited at the higher fre-quencies by local vibrations of small elements of the beams.