傳統木棟架中木板壁之斜撐模擬

Compressive Bracing Model for the Panel Wall Infilled in Traditional Wooden Frame

台灣地區之木造古蹟歷史建築物，常於木棟架中崁入木板片用以隔斷室內空間。相關地震案例均顯示，木板壁在地震時為整體結構抵抗面內力之重要元素。因此在調查研究或修復規劃設計過程進行耐震評估時，木板壁之效應有必要加以納入，以使評估結果更為合理。針對嵌入木棟架之板壁，本文探討以等值壓力斜撐來模擬。模擬過程，首先計算木板壁在水平面內力作用下之加載-位移關係。計算時，板片間竹釘提供之抗剪能力，以及板片迴轉擠壓框樑造成額外變形納入考量。其次，依據木板壁加載-位移關係曲線彈性階段之剛度，本文定義木板壁等值斜撐之有效寬度，並建議非線性分析時，板壁斜撐四個不同性能點之塑性鉸設定參數；其中斜撐降服點定義為框樑開始產生降服時，極限加載點取竹釘達剪力破壞點，而斜撐最大變形則取板片框樑達容許承壓應力時，木板壁之對角壓縮量之1.5 倍計算。利用本文之木板壁等值壓力斜撐模擬，台南市市定古蹟「鹽水八角樓」之靜態推垮分析結果顯示，板壁有助木棟架剛度與水平耐力之提昇，另外分析亦顯示在棟架結點嚴重破壞後，部分板壁才剛進入降伏，此狀況有助防止整體結構完全崩塌。

For the traditional wooden building in Taiwan, the wooden panels are adopted to partition the interior space and infilled piece by piece in the wooden frame. According to the building damage investigation after earthquake, it is observed that these wooden walls act as an element of the lateral resistant system, especially in the stage of large deformation. Thus, in the seismic assessment of this kind of traditional building, the wooden panels should be well considered in the model to be analyzed. In this study, the panel walls infilled in the wooden frame of traditional building is tried to be modeled as an equivalent compressive bracing. For the modeling, firstly, we calculate the load-displacement relationship curve of the panel wall. The dowel action of bamboo nails between two panels and the rocking behavior of the panels caused by the compressive deformation of the confining timber was also counted in the calculation. Second, the effective width of the equivalent bracing is defined in accordance with the stiffness of the panel wall in the elastic stage. Then, four performance stages of the bracing has been suggested to define the plastic hinge properties. In the four performance stages, the yielding strength of the bracing is defined as the confining timber begin to yield, and the ultimate strength is reached when the dowel action of bamboo nails failed. The maximum deformation of the bracing is assigned as 1.5 times the diagonal compressive deformation of panel wall. The diagonal deformation is calculated when the confining timber reached its allowable bearing stress. The bracing model has been used in the pushover analysis of a frame of Yanshuei Octagonal Display Hall - a registered heritage architecture of Tainan City. The analysis shows the panel walls will increase the structure stiffness and ultimate resistant load. Besides, it is also observed that several panel walls just begin to yield, when the frame joints have seriously damaged and the structure has experienced large deformation, which will avoid the structure to be completely collapsed.