FREE-VIBRATION ANALYSIS OF INSULATING GLASS UNITS

Modern insulating glass (IG) units consist of two glass plates, normally rectangular, placed parallel to each other. The plates are joined by a perimeter spacer and the unit is sealed so as to be air tight. Such IG units are widely used for thermal and sound insulation in modern buildings. An IG unit responds dynamically when exposed to wind loading. Fluctuating winds induce vibrations in the exterior glass plate and, in turn, this plate induces motion of the air enclosed between the plates and vibration of the interior plate. Hence, there is dynamic interaction between the two plates and the air trapped between them. A rigorous dynamic analysis is needed to determine the response of IG units to wind loading. As a first step, it is essential to study the periods of the fluid-plate system. In the present work, the two plates are assumed to satisfy small deflection plate theory. The air trapped between the plates is assumed to be irrotational and inviscid, but compressible, and it is assumed to satisfy the small amplitude equations of gas dynamics. A mathematical model is developed to study the interaction between the plates and the enclosed air. Assuming all edges of the plates to be simply supported and the perimeter spacer to provide a rigid boundary on the air space, the governing dynamic equations of the fluid-plate system are solved for free vibration response of the system. It is found that even plate modes are coupled with odd fluid modes and vice versa. The coupled frequencies of the fluid-plate system exhibit decreased magnitudes compared with the corresponding uncoupled plate frequencies. The information obtained concerning the frequencies of IG units will be useful in further dynamic analysis of these units when subjected to fluctuating winds.