中華民國內政部建築研究所中華民國內政部建築研究所

一、研究緣起
隨著建築物多孔性外牆更加複雜多變的發展，基於台灣地區每年都有劇烈的颱風等極端氣候來襲考慮，諸如此類多孔性外牆的耐風設計成為亟需解決的問題。另一方面，多孔性外牆對於減輕建築物外牆風壓擾動的潛力甚大，除對於建築物的外觀有裝飾作用，亦有可能產生保護建築物表面構件的作用。設計多孔性外牆所應考慮的風荷載，因其外型變化較大，不易由規範或文獻中獲得參考設計風壓係數。因此評估其減抑建築物外牆風壓擾動效用及多孔性外牆本身的設計風載重，有必要加以深入探討，以提供業界使用。
二、研究方法及過程
本研究利用風洞實驗更深入的探討建築物多孔性外牆所受到的風荷載狀況，包括內外表面風壓及其氣動力特性的討論，考慮不同安裝方式或內外風壓的差異成為風荷載的來源，因此間距、安裝位置、風向等多項因素均有影響，量測對象主要為風壓分布狀況，採用風洞進行縮尺模型氣動力實驗並搭配極值推估，掌握建築物多孔性外牆的整體受風特徵，並建議設計風壓係數。
三、重要發現
1.外部風壓作用主要由建築物周邊流場與來流影響，對於多孔性外牆其上開孔狀況，未能達到改變建物周邊渦流形成與分布的程度，因此外部風壓特徵並未改變。
2.風攻角的改變對於多孔性外牆內外各部的尖峰風壓係數分布有所影響，本階段實驗成果顯示，以風攻角0度時，各面向的尖峰風壓係數變化範圍較廣，因此可主要以0度風攻角的情形下進行設計風壓係數的推估。
3.夾層相鄰空間不連通狀況下，多孔性外牆所受淨風壓平均風壓係數在本研究夾層間隔距離變化及不同開孔率條件下，平均值均接近零值，呈現接近內外等壓的狀態。
4.夾層相鄰空間不連通時，多孔性外牆之外部尖峰風壓係數與內部建物立面風壓尖峰風壓係數兩者差異不大，內部建物立面風壓尖峰風壓係數略小於外牆之外部尖峰風壓係數約0.1~0.2，顯示多孔性外牆對內部建築物所受尖峰風壓作用較輕微。
5.觀察多孔外牆的外風壓部分，迎風面的正風壓值達到最高，而側風面的負值則最低，且兩者的絕對值接近，因此對於外風壓的考慮，迎風面及側風面風壓作用均應加以計算，正負兩種情形均須考慮。
6.具備多孔性外牆及夾層間隔的方形斷面建物，四面夾層空間相互連通時，多孔性外牆淨風壓係數之尖峰值分布情形，類似於多孔性外牆背面尖峰風壓係數隨夾層間距而變化的趨勢，顯示外風壓係數主要由來流流場條件所影響，多孔性外牆背面風壓則受多孔性外牆設置條件(開孔率、夾層間隔)而變化，因此有相同的變化趨勢。
7.具備多孔性外牆及夾層間隔的方形斷面建物，四面夾層空間相互連通時，多孔性外牆在迎風面及側風面上，淨風壓尖峰風壓係數的分布有中央區及角隅區的差別，以角隅區尖峰值較高，與多孔性外牆背面風壓分布有相同特徵。
8.多孔性外牆不論其相鄰夾層是否連通，多孔性外牆對於減輕內部建築物立面風壓擾動均具有效果，其中開孔率較低的多孔性外牆其減輕的幅度較高。
四、建議事項：
【建議一】
建築物耐風設計規範與解說增加建築物多孔性外牆設計風壓係數及編製建築物多孔性外牆設計風荷載計算示範手冊：立即可行建議
主辦機關：中華民國風工程學會
協辦機關：結構技師公會
國內建築物耐風設計規範之設計風荷載計算方式對於建築規劃設計時之風荷載考量至關重要，目前規範對於外部被覆物風荷載已有建議之計算公式及係數，但對於外加具備高開孔率外牆的雙層外牆構型，其外牆應有的風荷載估算方式可加以補充。
建築物多孔性外牆設計風荷載依循目前我國「建築物耐風設計規範及解說」之外牆被覆物考慮方式，計算公式形式不變，仍採用外風壓減內風壓方式計算，其中外風壓係數採用目前外牆被覆物設計風壓係數，內風壓係數則使用本研究成果建議之背風面設計風壓係數。可增列於我國建築物耐風設計規範第3.3節，並於解說敘述中增加對於多孔性外牆設計風壓係數適用條件之說明。
結合規範條文之增訂，以實際建築案例尺寸、基地條件等具體資料，並在不同應用條件下如何選取參數做說明示範，建立計算示範手冊，有助於規範推廣利用。
【建議二】
建築物創新構型設計與風荷載計算技術開發：中長期建議
主辦機關：中華民國風工程學會
協辦機關：內政部營建署
建築技術、材料不斷的推陳出新，針對提升建築性能與節能永續等目標，創新構型及附屬構件的發展亦與日俱進，考慮台灣地區激烈氣候、強風作用等事件甚多，為確保不斷變化的建築新設計作品之耐風性能，應有相應的安全建議與相關設計流程。
我國建築物耐風設計規範採用的基本風荷載條件隨環境變遷及工程研究的進步，應有同步的修正，並參考國外建築耐風設計規範發展，規範逐步擴充我國建築耐風設計規範適用的範圍。目前對於構形複雜或非傳統造型建築構造物，多需透過風洞實驗進行風荷載評估，可透過蒐集多年來累積的實驗成果，整理歸納選擇合適的成果參用引入於規範中，有助於提高建築物耐風設計規範的適用性。

I.Background
With the more complex and changeable development of porous exterior walls of buildings, considering the extreme weather such as severe typhoons in Taiwan every year, the wind-resistant design of such porous exterior walls has become an urgent problem to be solved. On the other hand, the porous exterior wall has great potential to reduce the wind pressure disturbance on the exterior wall of the building. In addition to having a decorative effect on the appearance of the building, it may also protect the surface components of the building. The wind load that should be considered in the design of porous exterior walls is not easy to obtain the reference design wind pressure coefficient from the code or literature because of its large changes in appearance. Therefore, it is necessary to conduct an in-depth study to evaluate the effect of reducing wind pressure disturbance on the external wall of the building and the design wind load of the porous external wall itself, so as to provide the industry for use.
II. Research methods and processes
This study uses wind tunnel experiments to further explore the wind load conditions on the porous exterior walls of buildings, including the discussion of internal and external surface wind pressure and its aerodynamic characteristics, considering different installation methods or differences in internal and external wind pressure as the source of wind load Therefore, many factors such as spacing, installation position, and wind direction have an impact. The measurement object is mainly the distribution of wind pressure. For further analysis, a wind tunnel is used to conduct aerodynamic experiments on a scaled model and combined with extreme value estimation, which can effectively grasp the porous structure of buildings. It is recommended to design the wind pressure coefficient and help clarify the suppression of wind pressure disturbance on the facade of the building by the porous outer wall of the building.
III. Preliminary Conclusions
1.The effect of external wind pressure is mainly affected by the flow field and incoming flow around the building. For the openings on the porous outer wall, the formation and distribution of eddy currents around the building cannot be changed, so the characteristics of external wind pressure have not changed.
2.The change of the wind attack angle has an impact on the distribution of the peak wind pressure coefficient of each part inside and outside the porous outer wall. The experimental results at this stage show that when the wind attack angle is 0 degrees, the peak wind pressure coefficient of each face has a wide variation range. Therefore, the estimation of the design wind pressure coefficient can be carried out mainly in the case of 0 degree wind angle of attack.
3.Under the condition that the adjacent spaces of the interlayer are not connected, the average wind pressure coefficient of the net wind pressure on the porous outer wall is close to the zero value under the conditions of the interlayer interval distance and different opening ratios in this study, showing close to the inside and outside, etc. pressed state.
4.When the adjacent spaces of the mezzanine are not connected, there is little difference between the external peak wind pressure coefficient of the porous outer wall and the peak wind pressure coefficient of the internal building facade, and the peak wind pressure coefficient of the internal building facade is slightly smaller than the external peak wind pressure coefficient. The external peak wind pressure coefficient of the wall is about 0.1~0.2, indicating that the effect of the porous external wall on the peak wind pressure of the internal building is relatively slight.
5.Observing the external wind pressure part of the porous outer wall, the positive wind pressure value on the windward side is the highest, while the negative value on the crosswind side is the lowest, and the absolute values of the two are close. Therefore, considering the external wind pressure, the windward side and The effect of wind pressure on the crosswind side should be calculated, and both positive and negative situations must be considered.
6.For a square-section building with porous exterior walls and interlayer intervals, when the interlayer spaces on the four sides are connected to each other, the peak value distribution of the net wind pressure coefficient of the porous exterior wall is similar to that of the peak wind pressure coefficient on the back of the porous exterior wall with the interlayer. The trend of changing with spacing shows that the external wind pressure coefficient is mainly affected by the flow field conditions of the incoming flow, and the wind pressure on the back of the porous external wall is changed by the setting conditions of the porous external wall (opening ratio, interlayer spacing), so there is the same Trend.
7.For a square-section building with porous outer walls and interlayer intervals, when the interlayer spaces on four sides are connected to each other, the porous outer walls are on the windward side and the crosswind side, and the distribution of the peak wind pressure coefficient of net wind pressure has the central area and the corners. The difference between the corner areas is that the peak value of the corner area is higher, which has the same characteristics as the wind pressure distribution on the back of the porous outer wall.
8.Porous exterior walls Regardless of whether their adjacent interlayers are connected, porous exterior walls are effective in alleviating wind pressure disturbances on the facade of internal buildings. Among them, porous exterior walls with lower porosity have a higher degree of mitigation.