WIND EFFECTS ON CYLINDRICAL CABLE ROOFS

Abstract

Evaluation of design wind loads on structures requires information on design wind speed and pressure or force coefficients besides other parameters. Whereas such information on flat and pitched roofs is available in most codes of practice as well as in literature, similar information for domical, cylindrical, hyperbolic and other curved roofs is scanty. Another aspect which is important in the study of structures under wind loading, particularly for flexible or slender forms, is the dynamic effect of wind. Whereas for the more rigid forms of structures a study on rigid models to determine the mean wind loads can be adequate, an experimental study of aerodynamic oscillations of the flexible structures requires testing on aeroelastic models for which proper modelling of stiffness and mass is also necessary in addition to appropriate modelling of the geometrical parameters. In this thesis a study of the effects of wind on curved roofs has been made, with particular emphasis on cylindrical roof surfaces representing cable-suspended roofs of this form. This choice has been made for the reason that cable roof systems have been finding extensive application to cover large column free areas because of their efficiency, aesthetically pleasing appearance, short erection time and little or no formwork requirement. The study was carried out in three phases in the following order. (viii) (1) The rigid models of a cylindrical roof over a rectangular plan were tested in the wind tunnel in order to measure the mean and fluctuating pressures at various points on the roof surface. The effects of various geometric and flow parameters such as sag to span ratio, height to span ratio, wind incidence angle, wind velocity, turbulence intensity, permeability etc. on wind pressure distribution were also studied. (2) Aeroelastic models of a cable roof were designed, fabricated and tested in the wind tunnel to measure the dynamic response under wind loading. (3) An algorithm and a computer programme for dynamic response analysis of cable roof systems were developed and the response of the roof was obtained theoretically using the wind loading obtained from rigid model tests as externally applied loads. This response was compared with that obtained in phase two above.