等壓雨屏牆風載之研究

Wind Loads on Pressure Equalized Rainscreen Walls

雨屏牆構法系統是由外部雨屏與內部氣屏及中間空氣層所構成的外牆構造，藉外氣導入中空層來達成雨屏內外的等壓性能，等壓性能的優劣具有影響中空層的排水性能與雨屏所受風載，而此構法除了新建築的應用外對於既有建築外牆的更新亦為頗值得應用的構造方法。歐美國家對雨屏研究發展至今約有60年，初始乃由防水觀念而起，再衍變為以開放式接縫達成等壓來排水，接續再提出利用等壓可減輕雨屏風載的相關研究，但這其中各參數影響雨屏等壓性能在減輕風載的標準尚無法一致；因此本研究經由文獻彙整影響等壓雨屏牆風載的因子，先以點支撐雨屏牆構法為研究對象，再選定雨屏透風孔幾何形狀、透風面積、中空層容積及風向角作為實驗參數，透過風洞實驗在均勻流場下進行測試，以無因次壓力係數演算雨屏內外風壓差與評估雨屏的等壓性能。實驗結果得知在風速13m/s透風開口率0.6%至3.3%的範圍下，開放式接縫透風形狀等壓性能略小於其他幾何形狀雨屏，但仍可達到約78％；試體長寬比值為1時，風向角在75°時出現較差的等壓性能；並彙整各參數對雨屏等壓性能之影響，以提供國內建立雨屏牆風載設計指南的基礎資料。

Pressure equalized rainscreen(PER) wall is the combination of an external rain screen, an internal air barrier and an air cavity in between. The pressure equalization is achieved by introducing the outside air into the air cavity. The performance of pressure equalization affects both the watertightness and the wind loading of the rain screen. PER wall is applied not only to new buildings, but also it can be adopted for re-cladding of the existing buildings. Rain screen walls have been developing for the past 60 years in America and Europe. The concept was initiated from waterproof, and then developed to rain penetration control system by open joint design. However, recent research shows the wind load acting on the rain screen can be reduced due to pressure equalization. However, no standard or guideline is presented to describe how various parameters contribute to the wind load reduction on the rain screen. This research aims to investigate how various parameters affect the wind loading on the rain screen by identifying the parameters through historic documentary study, employing point support system as the research object, analyzing the experiment parameter of geometry of venting holes on rain screen, vent areas, cavity volume and wind direction via wind tunnel test, and calculating the pressure difference across the rain screen while evaluating the performance of pressure equalization. This results of experiment indicate that the pressure equalization performance on rain screen wall with open joint is lightly lower than those with other geometries, while the vent area proportion ranges at 0.6%~3.3% under the wind velocity of 13m/s; however, 78% of performance is still given. When the relative model length/width ratio is 1, the wind direction at 75° gives a lower performance. The experimental data can be further used to establish a guideline for reducing wind load on the PER wall.