以高強度錨栓連接外加RC構架之補強工法

Abstract

於1999年921地震後，可觀察到中小學校舍之震害尤其顯著，雖校舍結構之設計地震力較一般樓房高出四分之一，但校舍卻是破壞最為嚴重的建築物，台灣之中小學校舍除了作為教育場所外，大地震過後亦常當作災民臨時收容所，因此，必須透過補強之方法提升其耐震能力。國家地震工程研究中心針對校舍結構耐震之問題提出一套耐震能力評估與補強流程，倘若符合補強經濟效益，即可作耐震補強之設計。台灣目前廣泛使用且經實驗測試驗證可行之補強工法為擴柱、翼牆與剪力牆，上述補強工法之劣勢為補強過程會影響(損壞)到既有建築物之運作功能，故本研究欲導入目前國內較少使用之補強工法，即為外加RC構架補強工法，盼該工法能充分發揮其優勢。 外加RC構架補強，即於既有建物之弱向兩旁新建混凝土構架，與既有構架共同抵抗地震力以提升結構物之耐震能力，本研究採高強度錨栓連接既有建物之梁與外加RC構架之梁，透過錨栓傳力進行補強，故錨栓傳遞地震力強度之容量為研究主軸。該施作方式優點為接合確實、錨定力提升、減少腹地空間使用以及增加施工穩定性。 此外，本研究亦提出外加RC構架設計流程，第一部分為構架設計，首先設計構架斷面尺寸，接著參考國家地震工程研究中心所出版之臺灣結構耐震評估側推分析法第四版之建議，使用ETABS輔助進行非線性靜力側推分析，確認側推曲線符合要求，第二部分則細部設計高強度錨栓所需提供數量、T頭錨定端板以及埋入深度，再進行錨栓強度檢核，最後，取既有校舍之一跨構架作為示範例。 本研究參考外加RC構架補強校舍初步評估與設計，透過一棟實際校舍案例(後甲國中德育樓既有校舍)進行耐震評估及補強，證實外加RC構架補強不僅可提升結構物耐震能力，亦可使其他樓層一齊參與消能、改變原有結構系統不良破壞模式，未來應考慮應用於醫院以及其他公私有建物補強。 鑒於目前國內少有與高強度錨栓傳遞地震力之容量相關試驗，本研究設計五座RC構架試體，其中包含一座既有空構架試體與四座外加RC構架補強試體－於國家地震工程研究中心之MATS系統進行錨栓強度容量試驗，並設計一套配合實驗之鋼製夾具，與常見之植筋補強方式比較，提出另一補強連接工法。由試驗結果可得知使用外加RC構架進行補強，其試驗之側向載重、勁度以及韌性容量均能有效提升，驗證該補強方法確實能達到其對既有校舍補強之效果。

After the largest Earthquake in Taiwan’s history on September 21st, 1999, the damage of school buildings were of particular significance. Although the seismic design force of the school buildings were one-quarter higher than the general structure of buildings in Taiwan, they were still the most damaged buildings. In addition to serving as a place for education, school buildings are often used as temporary shelters for victims after a major earthquake. Therefore, they must be strengthened to improve their earthquake resistance. The National Center for Research on Earthquake Engineering proposed some complete procedures for seismic evaluation and seismic retrofit of school buildings, which we could carry out if it meets the economic benefits of reinforcement. The typical retrofit methods of buildings in Taiwan include RC jacketing, wing wall and shear wall, but the buildings were affected during the construction by those methods. This research proposes that by adding RC external frames to the retrofit method would be more effective, a technique seldom used in Taiwan. Adding RC external frames is a retrofit method by which two external frames are added along the weak direction of existing buildings to raise the seismic resistance. In this research, RC external reinforced concrete frames were connected to existing buildings using high-strength anchor bolts. The high-strength anchor bolts transfer the seismic force from existing building to external frames. Therefore, this method would be appropriate for use in school buildings. The anchor bolts is able to dissimilate seismic force. The advantages of this construction method are: reliable jointing, improved anchoring force, reduced use of hinterland space, and furthermore increased construction stability. To use this method, we must understand the design process of adding RC external frames. First, design the frame with cross-sectional dimensions, then from a nonlinear static pushover analysis, the capacity curve is achieved and confirmed. Second, have a detailed design of the number of high-strength anchor bolts, the T-head anchoring end plate, the depth of embedment, and then check failure modes of the anchor strength. Finally, one of the existing school building will be taken as an example. After the retrofit, it was confirmed that the retrofit design could eliminate the problems of the poor failure mode of the existing structure. We hope the benefits would not only be used for school buildings, but also for hospitals or other public and private buildings. Given the fact that there is little related experimental information about the capacity of the anchor bolts to dissimilate seismic force, this study has designed five reinforced concrete frame specimens, including an existing frame specimen and four new frame specimens. They were created by adding RC external frames, experimental anchor bolts to strengthen the capacity test and by using a set of steel molds as well as steel beams at the National Center for Research on Earthquake Engineering. In conclusion, when compared with the common reinforcement method of post-installed rebar, the RC External frames method was superior. From the test results, it can be found that adding RC external frames can effectively improve the lateral load, stiffness and capacity.