Date of Award
1990
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The use of lightweight roofs for long span structures has become popular. Architects find these structures attractive because they allow for a wide scope of innovative design, and can be cost effective and aesthetically pleasing. Although extensive research has already been devoted to many aspects of lightweight structures, this thesis examines the effects of wall openings on self-supported roofs backed by cavities, the nature of the response of air-supported roofs to turbulent wind, and theoretical methods for response prediction.;The first part of the study comprises a free vibration analysis of self-supported, lightweight roofs backed by cavities with openings. A simplified theoretical approach is formulated to evaluate the modal parameters of the roof-air system considering air leakage through the openings, the pneumatic stiffness, and the structural and acoustical damping of the system. The accuracy of the approximate formulae is assessed by comparison with a complex eigenvalue analysis. An exact solution is derived to evaluate the modal parameters for a circular membrane roof backed by a cavity with openings. Closed form solutions are presented for the damped response of circular membrane roofs backed by cavities with openings.;Free vibration laboratory experiments were conducted on two different structural models to verify the theoretical approach. The first model had a membrane roof, and the second had a flexible plate roof. The effects of wall openings and volume scaling on the roof-air system were examined and the experimental results were then compared with the theoretical ones.;The second part of the study is an examination of the behaviour of air-supported structures. The free vibration of cylindrical and spherical air-supported structures is investigated analytically for different internal pressures and enclosure volumes and the results are compared with those obtained from a finite element solution.;Wind tunnel tests were conducted on an aeroelastic model of a hemispherical, air-supported structure to investigate the wind-induced response and the internal pressure fluctuations. Parameters considered in the aeroelastic experiments included different gradients wind speeds, exposures, enclosure volumes and internal pressures.;A semi-analytical approach is established for predicting the wind-induced response of air-supported structures. This approach depends on external pressure measurements and static deflections. A rigid hemispherical model was tested in a boundary layer wind tunnel to measure the external pressures for different exposure conditions. For different internal pressures, the static deflections were calculated theoretically using the finite element method. The predicted response results of the semi-analytical approach agree well with the experimental results.
Recommended Citation
Kassem, Magdy Elsayed, "Dynamics Of Lightweight Roofs" (1990). Digitized Theses. 1981.
https://ir.lib.uwo.ca/digitizedtheses/1981