RC牆板厚與邊界柱深相互間關係對構架耐震行為之研究

Abstract

街屋或校舍結構之含RC牆構架受面內側力試驗結果顯示，RC牆產生對角斜裂縫剪力破壞，且牆板裂縫延續至邊界柱，使柱一併產生剪力破壞，由試驗破壞包絡線顯示，構架含RC牆破壞時，邊界柱已喪失其獨立抗彎構架的行為。然而，EERI & IAEE之低矮型圍束砌體建築物耐震設計規範指出，當加強磚造構架之邊界柱深小於1.5倍磚牆厚度時，發生由牆板延續並貫穿柱之對角斜裂縫破壞；當加強磚造構架之邊界柱深大於2倍磚牆厚度，對角斜裂縫只出現在磚牆上，磚牆與柱交界面則出現垂直裂縫，柱與磚牆分開獨立變形，使柱保有獨立抗彎能力。 我國耐震設計規範要求牆體需一併納入結構分析計算，而工程師除了符合規範剪力牆要求之牆體外，其餘RC牆均忽略不算。街屋或校舍結構之含RC牆構架受面內側力試驗結果顯示此作法不正確，中小學校舍補強評估方法已予以修正。至於大尺寸柱配合薄的RC牆之大樓建築結構，邊界柱是否於牆板破壞時一併產生破壞，抑或有類似加強磚造構架之行為。本研究共設計製作四座縮尺50%試體進行試驗，一座為空構架，另三座為填充6cm厚RC牆構架，四座試體之構架均採用方形柱，尺寸分別為20cm、35cm及50cm，本研究結果顯示隨柱深對牆厚比愈小，構架之韌性愈差，且試體在極限強度後仍保有純構架之行為愈不明顯。

As shown in the lateral loading test results of the town house or school building structure with RC wall frame that when failure occurred diagonal cracks propagated through the RC walls and the tie-columns. Analysis from failure envelopes reveals that the tie-column failed to fulfill its role as a solely moment-resisting element due to it shear inability. Also indicated in SEISMIC DESIGN GUIDE FOR LOW-RISE CONFINED MASONRY BUILDINGS by EERI & IAEE that the mechanism which failure took place in the form of a single diagonal crack which propagated through the walls and the tie-columns can be expected to occur in buildings with small RC tie-column sizes, where tie-column depth does not exceed 1.5 times the wall thickness. When the tie-columns and tie-beams have larger sections (depths in excess of two times the wall thickness), diagonal crack appeared only in masonry wall panel while vertical crack occurred in the interface between masonry wall and the column, which lead to the separation between wall and column. Then the tie-column becomes the solely moment- resisting member. Although the seismic specifications require that the walls need to be included in the structural analysis, engineers usually ignore RC walls except shear walls in their calculation. This practice has been proved to be inappropriate from the aforementioned test results and thus modified in the recent reinforcement and evaluation method of elementary school buildings. As for mansion structure which consists of large column with thin RC wall, whether the tie-column would fail together with the walls or like that of a confined masonry wall panel is the main concern of this research. In this research, four 50% reduced scale frames, one without infill RC wall and the other three with 6cm infill RC wall, were tested. The columns of these four frames are all square with depth 20cm, 35cm and 50cm respectively. It is shown in the test results that the toughness of the frame decreases with increase of the column depth/ wall thickness ratio. Also the retained pure frame behavior post-strength become less obvious with increase of the column depth/ wall thickness ratio.