| Summary: | 碩士 === 淡江大學 === 土木工程學系碩士班 === 103 === Due to the progress of architectural technology and building materials, high-rise buildings became a viable solution to the irreversible trend of urbanization and population concentration. To overcome the short of land or for getting better view, many tall buildings are built on hill top or escarpment. However, the design wind loads for those tall buildings are based on same procedure for buildings on flat terrain with some adjustment on wind speed. This thesis studied the wind profile and aerodynamic characteristics of a square shaped tall building on an escarpment.
Firstly, wind tunnel experiment was carried out to study the flow field characteristics of wind passing over an upwind slope of 11.3˚ escarpment in suburban terrain (α=0.24). The mean wind speed and turbulence statistics are investigated. Results indicate that wind speed-up phenomenon (increase of speed) occurred significantly around the tip of the upwind slope. The turbulence intensity decreases gradually as the wind flows from the toe of upwind slope.
An acrylic square shaped building model with side ratio of L/B=1 and aspect ratio h/√A=3 was constructed for wind pressure measurement. Results indicate that the escarpment casts little effects on the mean pressure coefficients. The R.M.S. pressure coefficients are significantly larger in the case of escarpment than on ground level. The acrosswind force spectrum exhibits distinct peak at reduced frequency fB/UH=0.1 due to vortex shedding. Square building has larger spectral peak when locates on escarpment than on the ground. However, both cases has similar spectral estimates in the higher frequency region that close to the building natural frequencies. In other words, the resonance part doesn’t have much influence, hence, it doesn’t has much influence on the acrosswind design wind load of high-rise buildings. Then, the alongwind, acrosswind and torsional design wind loads were calculated based on the wind tunnel measurements and compared with those of building wind code. The results show that the current wind code tends to significantly underestimate the alongwind design wind load.
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