Experiments with Free Vibration of Light Roofs Backed by Cavities

Abstract

This paper complements the theoretical study of the same subject. The aim is to verify the theory formulated in the companion paper. Free vibration of large‐span, self‐supported, lightweight roofs backed by cavities with wall openings is experimentally investigated in the laboratory using two model roofs: a circular membrane roof and a flexible, circular plate behaving in a flexural way. Similarity requirements of the roof‐air system are reviewed. The influence of wall openings on the frequencies and total damping of the structure is investigated. Comparison of the experimental results with those of the theoretical analysis formulated by the writers is made. Excellent agreement between the theory and experiments is obtained. The notions of a leaking kettledrum and a Helmholtz oscillator with a flexible wall are confirmed. The air movement through the wall openings as well as the acoustical damping associated with the motion of both the roof and the air mass at the openings have significant effects on roof natural frequencies and modal damping. The volume of the enclosure under the roof has also a marked effect.