Yasushi Uematsu

The present study examines the wind-induced behaviour of free-standing membrane canopy roofs with various types of roof-supporting systems and presents wind force coefficients for designing such roofs. The effects of roof deformation and choice of roof-supporting system on wind force coefficients are investigated. The characteristics of wind-induced responses of the roofs are taken into account for improving the wind force coefficients that we previously proposed based on the results of wind tunnel experiment with rigid roof models.

The design of low-rise buildings such that they can handle wind loads makes it necessary to accurately evaluate those wind loads, both on the structural framework and on the cladding/components. To this end, it is necessary to fully understand the characteristics of the wind near the ground around a building. This study sets out to develop a quantitative means of estimating the turbulence of the wind near the surface of the ground, based on field measurements obtained at different points across Japan. The surface roughness is evaluated based on several factors taken from a building information database. The relationship between these factors and the turbulence of the wind is discussed. The effect of the observation height, relative to the surface of the ground, on the turbulence is also investigated.

Wind loads on cylindrical free-standing canopy roofs were investigated in a wind tunnel. First, the overall aerodynamic forces and moments were measured using a force balance. The distributions of net wind pressures provided by the difference between wind pressures on the top and bottom surfaces of the roof were then measured along two representative arc lines. Based on the results, the net wind-pressure coefficients for designing such roofs are proposed as a function of the rise-to-span ratio for two representative wind directions: one perpendicular to the eaves, the other inclined at an angle of 45° to the eaves. The roof is divided into three zones and constant net wind-pressure coefficients are specified for these zones. Two load cases providing the maximum tension and compression in the columns supporting the roof are considered as the most important load effect for discussing the design wind loads.

The present paper discusses the mechanism of the wind-induced scattering of permeable unit flooring decks loosely laid on the rooftops and balconies of high-rise buildings. Firstly, the scattering mechanism of decks was investigated, based on a blowing test using a blower and actual decks. Subsequently, a simulation model was constructed for estimating the internal pressures under the decks (pressures acting on the bottom surface of decks) obtained from a wind tunnel experiment – this is based upon the unsteady Bernoulli equation and the time history of external pressures on the rooftop and balconies. Combining the simulated internal pressures and the experimentally obtained external pressures, the time history of net wind pressures acting on the decks were computed. Finally, the threshold wind speed of scattering (scattering wind speed) was obtained by applying the scattering mechanism to the simulated time history of the net wind pressures.