低矮建物屋頂表面之極值設計風壓係數探討

國內廣泛應用於廠房、校舍等結構普遍具有造價低廉且施工容易的優勢，然而此類結構多為輕材質且強度較低，設計結構載重時耐風設計比耐震設計來得重要。再者，此類結構外型上雖然歸類為低矮建物，但通常其屋頂多屬跨度大且具有斜屋頂的特徵，在角隅處容易因流體的分離及再接觸，而產生較大的負風壓分布，使得風載重設計更需謹慎評估。低矮建物屋頂表面的設計風載重探討在過去的文獻中多有討論，但所依據的風洞實驗結果通常不足以進行足夠筆數的極值分析，因此多以假設極值風壓為甘保分布(Gumbel Distribution)，進而求取78%非超越機率(Cook and Mayne係數)為極值風壓設計值。本研究首先進行長時間風洞實驗取得足夠數量之風壓資料進行分析，採用廣義極值分布模型進行參數擬合，發現大部分風壓孔的極值風壓為(Non-Gumbel Distribution)，分布情形與風壓孔位置、屋頂斜率及風向角均有關，本研究嘗試以廣義極值分布模型配合極值變異數進行設計風載重理論的疊代，求取出最佳設計百分比及其相對應之最佳設計風壓係數，最後再以屋頂整體升力係數作為與我國規範之比較，指出規範過於保守以及以甘保分布作為前提的誤差影響。

關鍵字

低矮建物；極值風壓分布；風洞實驗；設計風載重

並列摘要

Domestic factory buildings are often constructed in the form of light steel frames. Light material and long span are two common features among them. Due to this, wind resistant design is sometimes prior to earthquake resistant design for its structural safety concern. In the past, huge amount of research results have been accumulated for low-rise buildings; however, none of them was conducted to collect enough sample records for examination of the behavior of the extreme value distribution. In general, the extreme values were assumed to be Gumbel distributed and the design coefficient was evaluated by the Cook and Mayne method. In this study, non-Gumbel distribution is fitted by Generalized Extreme Value Distribution model. By concerning the variation coefficient of extreme values, the iterative process of design wind loads is adopted to find the optimal design fractile for pressure coefficients. Comparisons are made to tell the differences caused by Gumbel assumption for extreme values. Several proposed methodologies are also attempted for an appropriate choice when the sample records are few. Finally, the lift force coefficients over the roofs are compared with the current domestic code for a clear picture on this research theme.

並列關鍵字

low-rise building ； non-gumbel distribution ； wind tunnel test ； design wind loads

國際替代計量

低矮建物屋頂表面之極值設計風壓係數探討

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