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  • 學位論文

含薄型挫屈束制支撐構架耐震行為研究

Research and Development of Thin Buckling Restrained Braces for Seismic Buildings

指導教授 : 蔡克銓

摘要


挫屈束制支撐(BRB)為近幾年來被廣為使用結構制震系統,經過多年的研究與推廣,市面上有各種各樣不同的斷面型式,然而為提高可使用的樓地板面積,如何降低斜撐的厚度也就越來越有研究的必要。傳統大型圍束單元的BRB較無法符合此要求,薄型化與輕量化BRB的需求可能會越來越高;當斜撐之圍束單元往薄型化發展時,其束制能力就顯得重要。支撐之整體撓曲挫屈必須防止之外,但是局部挫屈亦須避免;薄型化BRB的設計方式與力學行為,為本研究探討重點。 本研究包含: (1)研發全鋼薄型挫屈束制支撐,並透過構件試驗施加反覆載重測試其反應,並探討其力學行為。(2)研發三種不同形式之薄型BRB,包括利用矩形鋼管內灌入水泥砂漿做為圍束單元,並透過實尺寸三層樓構架試驗對其中一種薄型BRB進行測試。(3)以擬動態實驗方式進行構架試驗,在實驗前後利用PISA3D和OpenSEES非線性結構分析軟體,對實驗結果進行預測與模擬。(4)透過含薄型BRB之構架與構件單元試驗結果,探討薄型BRB核心板之高模態挫屈行為,以及其所引致之局部挫屈破壞模式,並利用ABAQUS有限元素分析軟體之3D solid元素和雙線性材料,建立數值模型模擬實驗反應,提出局部挫屈之檢覈方式。 由四組構件試體試驗結果得知全鋼薄型BRB可以達到薄型化與輕量化的需求,除了端部的圍束條件需要被改善之外,圍束單元可以適時發揮束制效果。實尺寸三層樓構架施以10/50地震歷時之擬動態試驗中,一樓其中一組薄型BRB於試驗中發生局部挫屈後斷裂;其他五組試體表現良好,每層兩支BRB在構架中足以承受約七成以上的樓層剪力,可以消散大部分地震所帶來的能量;發生破壞的斜撐為局部挫屈破壞。透過ABAQUS有限元素軟體分析或是利用雙模數理論(double modulus theory)皆可以適當預測核心段的高模態挫屈波長,本研究結果顯示BRB核心段於極大的軸壓應變下,高模態挫屈波長約為15至20倍的核心板厚;藉由此挫屈波長與脫層單元厚度的幾何關係可推導出圍束單元於BRB於最大軸壓力下所受到的側向接觸力,此與圍束鋼管所受到的側向力與水泥砂漿厚度有關,本研究提出圍束鋼管的設計方法,以防止發生局部挫屈發生。

並列摘要


The Buckling Restrained Braces (BRBs) have been widely used in seismic buildings around the world. However, in order to save more space in the buildings, the development of “Thin BRB” may be warranted. Because the flexural buckling and or the local buckling are prone to occur while the thickness of the restraining units are reduced, the research on the precise restraining mechanism and capability of a thinned BRB is required before the thin BRBs can be reliably used. The seismic resisting behavior and the design methods of thin BRB are the research priority of this thesis. This thesis includes: (a) research and develop the design of an all-steel thin BRB, verify the BRB design by conducting cyclic load tests; (b) develop three different types of thin BRBs using the hollow structural section and infill concrete as restraining unit, apply one type in a full-scale three-story BRB frame tests; (c) before and after the BRB frame tests using the pseudo dynamic procedures, predict and simulate the responses using both PISA3D and OpenSEES programs; (d) the high buckle mode of the BRBs were investigated using bi-linear solid elements and ABAQUS models, the failure modes of restraining members were investigated for BRBs in the frame and component tests. The design methods for the restraining units to prevent the local buckling are proposed. The proposed designs of the all steel thin BRB reduce the brace thickness and economize the use of the steel material. Based on the cyclic load tests of four all-steel BRBs, the proposed all-steel cross section, but not the end connection details, worked well during the component tests. In the pseudo dynamic frame tests using the 10/50 earthquake, except the thin BRBs, all of the standard concrete-infill type BRBs performed well. The braces in each story resist more than 70% of the story shear and dissipated most of the seismic input energy. During the pseudo dynamic test, one of the two thin BRB in the 1st story failed due to the cyclic local buckling and the subsequent fracture. It is found that the the wave length of the high mode buckleing of steel core observed in the tests could be simulated by finite element analysis and hand calculation using double modulus theory for the steel core. Gain the relationship between contact forces induced by high mode buckle and the sizes of restraining members to prevent failure due to local buckling of BRB core. Research results suggest that under severe compressive strains, the BRB steel core high mode buckle wave length is about 20 times the core plate thickness. The local buckling design load for the steel casing can be determined. It depends on the peak brace compressive load, the thickness of the unbonding layer, the thickness of the concrete between the steel core and the steel casing, and the buckle wave length.

參考文獻


27.劉家源(2007),”全鋼型挫屈束制支撐局部挫屈研究” 國立台灣大學土木工程研究所 碩士論文 蔡克銓教授指導
26.魏志毓(2006),”挫屈束制支撐局部挫屈與構架耐震效益分析研究” 國立台灣大學土木工程研究所 碩士論文 蔡克銓教授指導
25.蔡政育(2005),”實尺寸兩層樓挫屈束制支撐子結構雙向受震擬動態試驗與分析” 國立台灣大學土木工程研究所 碩士論文 蔡克銓教授指導
24.蕭博謙(2004),”實尺寸三層樓挫屈束制支撐CFT柱構架擬動態試驗行為與分析” 國立台灣大學土木工程研究所 碩士論文 蔡克銓教授指導
1.AISC(American Institute of Steel Construction) 341-05, (2005), “Seismic Provisions for Structural Steel Buildings.” American Institute of Steel Construction, Chicago.

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