斜撐面內挫屈之特殊同心斜撐構架耐震行為研究

Abstract

為抵抗地震，特殊同心斜撐構架藉由斜撐構件受拉降伏與受壓挫屈進行消能行為，而傳統斜撐與接合板設計將使斜撐挫屈方向朝面外變形，而由先前研究顯示此面外變形量可能高達40公分，容易對包覆斜撐之牆面造成破壞，甚至對建築內使用空間之人員以及器物之安全產生威脅。本研究透過連接板的作用將斜撐挫屈方向轉變為朝面內變形，並進行兩層樓實尺寸構架之試驗以觀察斜撐面內挫屈變形之行為反應，並利用有限元素分析軟體ABAQUS建立有限元素模型模擬試體反應。希望能建立一套含斜撐面內挫屈之構架設計程序，並以有限元素模型分析輔助研究，以便降低進行實驗所需的時間與金錢成本。 本研究所採試體之構架系統採用先前曾在國家地震中心測試過三次TCBF與一次BRBF之梁柱構架，僅將斜撐與接合板拆卸更換。試體高6.66公尺，寬6.7公尺，斜撐排列形式為大X形，斜撐尺寸為H175x175x11x7.5，與第二次TCBF試驗採用之斜撐相同，但本研究因需配置額外的連接板而使得斜撐長度略短，接合板則採用規範建議之UFM進行設計，與第二次TCBF橢圓形凹折設計不同。試驗藉由千斤頂在頂樓樓板中央施力，進行反覆側推測試。 此次試驗發現東側兩支斜撐先後發生挫屈後，西邊兩支斜撐相隔甚久才發生挫屈，造成前述東側兩支斜撐挫屈處之非線性應變過大，提早在出現局部挫屈現象後而有細微裂縫發展，最後導致斜撐較面外挫屈之TCBF之H型斜撐更早破裂而整體結構壽命較斜撐面外挫屈構架更短。推測其原因可能在於斜撐長度較短，韌性變形行為較差。因此尋求改良設計之方法，另以平衡設計的觀點容許接合板及連接板與斜撐共同進入非彈性階段但確保最終破壞僅發生在斜撐構件，以便提升整體系統的韌性，也能對連接板及接合板進行較經濟之設計，本研究也探討如何使得斜撐長度增長，以便能發展出較佳的挫屈行為。另以generalized UFM進行接合板設計，結果可以設計出矩形接合板而不受傳統UFM限制，且節省切割成本。最後考慮將連接板與接合板相連之淨斷面問題從連接板移至相接之十字截面中，斜撐與連接板在工廠進行精密焊接而兩端各保留5公分之空隙以方便現地組裝，如此可以省去貼板且對斜撐柔度分佈與挫屈行為有正面幫助。進行這一連串改良設計後，希望能由下次試驗中證實斜撐面內挫屈變形之SCBF的較好設計方法。

For resisting earthquakes, the special concentrically braced frames dissipate energy by the braces yielding tension and buckling in compression. The tradition design of connection of gusset plates and braces make the braces buckle out-of-plane. The out-of-plane deformation can become 40cm in previous tests. The buckled braces probably damage the wall covering the braces even people or equipment nearby. The research transfer the braces buckling direction into in-plane by the knife plates, and test in a two story real size fame specimen to investigate the responses of the braces buckling in-plate. Then build a FEM model by ABAQUS to simulate the responses of specimen. Hope to establish a design procedure of frames in braces buckling in-plane. And use FEM model instead of real size test to reduce the cost of time and money. The specimen in this research have been used for 3 TCBF tests and a BRBF test. Only changed the gusset plates and braces, and kept the frame remain. The specimen is 6.66m tall and 6.7m wide. The arrangement of braces is X type. The braces is H175x175x11x7.5, same as the second test of TCBF. Because of additional knife plates, the braces length in this test is a little shorter than the second TCBF test. The gusset plate design use the UFM instead of ellipse bending design method. The actuator act on the middle of roof slab to proceed cyclic test. In this test, the two braces in east side buckled in sequence, then the two braces in west buckled after a long time. Large nonlinear strain happened on the local buckling area of the two east braces. Lead to the in-plane buckling braces fractured earlier than the second test of TCBF. The reason may be the shorter brace length result in poor ductile deformation behavior. In research of a improved design method, the concept of balance design is used to allow the knife plates, gusset plates and braces develop non-elastic behavior but make sure the fracture only happen in the braces. The balance design not only improves the system ductility but also the economy of gusset plates and knife plates. The research improve the braces buckling behavior by elongate the braces. Design the rectangular shape gusset plates using generalized UFM to break the shape restrain of original UFM and reduce the cutting cost. Consider to move the net section issue from the connection of braces and knife plates to the cross section of knife plates and gusset plates. The weld of braces and knife plates is accomplished precisely in the factory and keep 5cm slot in each end for fabricating. So we can save the cover plates and take advantage of uniform distribution of flexibility in braces and buckling behavior. After series of improve design, hope to demonstrate the better design method of the braces buckling in-plane in next tests.