陡坡對於高層建築風力特性的影響

現今隨著經濟的迅速發展以及建造建物技術的進步，高層建築有效解決都市用地狹小、人口稠密之問題，加上工程材料及施工技術之改良，部分建築也有往山坡地開發的趨勢。近年高層建築的設計高度逐漸增高，故對位處於強風盛行地區的台灣，高層建築所受的橫向側力除了地震力之外，風力之影響也日趨重要。本研究主要以鄉鎮地形其地況係數為0.24，陡坡坡度為11.3˚的條件下作為逼近流場，分別量測平地與陡坡的風速剖面與紊流強度。從實驗結果顯示風速剖面在陡坡的情況下會有逐漸加速的現象產生，而紊流強度則逐漸減小。並選用深寬比1，高寬比3之矩柱模型，以進行量測建築物表面風壓之風洞試驗。平均風壓係數之分佈則由等壓線圖得知在有陡坡情況下平均風壓係數不論在迎風面、側風面和背風面與平地結果相近，擾動風壓則可看出陡坡在側風面的部分明顯大於平地。橫風向風力頻譜在0.1的位置有明顯的窄頻尖峰其原因為渦散作用於模型體所造成。有陡坡的頻譜數值則明顯大於平地，說明了在陡坡的影響下橫風向渦散現象的影響更為顯著。在高頻處平地與陡坡趨於一致，代表共振部分影響很小，對低層建築設計風力影響較大，反之高層建築則影響較小。另根據實驗計算出建築物在有陡坡的情況下順風向設計風力、橫風向設計風力和矩扭轉向設計風力均與現行《建築物耐風設計規範》做比較，從結果得知規範在順風向雖有考慮加速現象但在迎風面與背風面外風壓係數仍比實驗值小，故在順風向風力規範趨於保守，橫風向因規範低估建築物在陡坡渦散效應的影響所以較不保守，扭轉向的部分差異不大，其原因為正方形結構體較不容易受到扭矩的影響有關。

關鍵字

高層建築；陡坡；設計風載重；風洞實驗

並列摘要

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.

並列關鍵字

High-rise buildings ； Escarpment ； Design Wind Load ； Wind Tunnel Test

參考文獻

5-4 蔡明樹,(2008),“高層建築順風向等值靜態設計風載重之研究”,淡江大學土木工程學系博士班論文,Jun.2008.

5-5 賴子晴,(2013),“不同矩形斷面之高層建築設計風荷載研究”,淡江大學土木工程學系碩士班論文,Jun.2013.

1-2 ASCE (2002). “Minimum design loads for buildings and other structures.” ASCE 7-02, Reston, Va., USA.

2-1 C. F. Cowdery, (1986), “Two topics of interesting experimental industrial aerodynamic”, symposium on wind effects on buildings and structures, National physical laboratory, Teddington.

2-3 J. Counihan﹐(1970)﹐" Further Measurements in a Simulated Atmospheric Bounday Layer "﹐Atmospheric Environment﹐Vol.4﹐pp.159-275.

國際替代計量

陡坡對於高層建築風力特性的影響

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