含磚牆RC構架面外受震行為研究

Out-of-Plane Seismic Behavior of Confined Masonry Walls

在台灣，含磚牆RC 構架為常見用於低層建築的構造方式。由過去的震害經驗中發現，磚牆除面內方向之受剪破壞外，亦有部份為面外方向倒塌。由於磚牆之面外強度遠小於面內，受震時，可能未發揮其面內強度即產生面外方向之無預警脆性破壞而倒塌；因此，實有研究其面外方向受震行為之必要。然而，現有之磚牆強度評估方法中，卻鮮少有考慮其面外方向之強度。故本文藉由參與國家地震工程研究中心所進行之現地校舍靜力推垮試驗，觀測並記錄其隔間磚牆受面外載重之結構行為，並由試驗結果發現內填磚牆受水平向集中載重時，會產生斷面受撓，並於上下兩端拉力側開裂，形成上下兩端為鉸支承般之剛體旋轉。本文即利用現地試驗中，所觀察之磚牆特性與其基本性質建立內填磚牆面外受力之壓桿模型，進一步推導磚牆之極限強度公式。與現地試驗結果比較，顯示由公式計算之磚牆強度理論值雖偏保守，但應為合理可用。

Confined masonry is theoretically studied and verified with experimental measurement to understand its out-of-plane behavior in this paper. As known for its construction economy and simplicity, confined masonry is commonly used for low-rise RC buildings in Taiwan. This construction is featured by the un-reinforced masonry (URM) wall and its out-of-plane fragility may cause sudden collapse and serious casualty as experiencing earthquakes. A thorough investigation on the URM walls is therefore necessary to understand the structural performance especially in extreme conditions. An analytical model has been developed to evaluate the structural behavior of the URM walls in the out-of-plane direction. Based on the empirical data acquired from the measurements in the in-situ tests, the critical properties, such as ultimate strength, are also calculated to provide important parameter for the construction design of URM walls. Under a concentrated loading on the top of the confined masonry, the analytical model supposes that the main cracks always generate and propagate at the top and the bottom of the wall while the region between the main cracks behaves as a rigid body. Furthermore, ignoring the axis force originating from the upper structure, the ultimate strength and the maximum displacement of the URM wall can be simply acquired by a strut model which the geometric compatibility is considered. The analytical model predicts reasonable results for the ultimate strength of the URM walls and conservatively agrees with the experimental measurements.