挫屈束制支撐(BRB)構架為近年來漸被重用的耐震建築結構系統,為減低BRB所佔空間而提高可使用的樓地板面積,如何降低斜撐的厚度成為重要的研究課題。薄型化的挫屈束制支撐設計必須防止整體撓曲挫屈破壞之外,亦須避免圍束鋼管的局部外突破壞。薄型化BRB的力學行為與耐震設計為本研究探討重點。本研究探討之薄型挫屈束制支撐核心板為單板型式,核心板在承受軸壓力時會產生高模態挫屈。波峰接觸到圍束單元時會有側向力,若向外傳遞之側向力超過圍束鋼管所能抵抗之強度,則圍束單元鋼管會有局部外突之破壞模式。本研究由高模態挫屈波長與脫層單元厚度的幾何關係,計算BRB核心板於最大軸壓力下,高模態挫屈時向外推擠之側向力,並利用ABAQUS有限元素模型分析探討側向力向外傳遞至圍束鋼管之範圍;假設圍束混凝土只傳遞側向力但不參與抵抗外突破壞,利用板降伏模型的極限定理計算圍束鋼管抵抗局部外突破壞之強度,因此可預測薄型BRB發生圍束鋼管局部外突破壞的可能。本研究利用八組薄型BRB試體在國家地震工程研究中心進行BRB構件反覆載重試驗,其中四組薄型BRB採用本研究建議之設計方法在核心應變超過0.03才發生鋼管局部外突破壞,試驗結果顯示BRB核心段在0.03以上的軸壓應變下,高模態挫屈波長約為8至10倍的核心板厚。ABAQUS模型分析結果顯示側向力向外傳遞範圍約與核心板寬與二倍包覆水泥沙漿厚度的乘積相當。試驗結果顯示薄型BRB發生鋼管局部外突破壞的範圍及模式與分析模型所預測相符,因此本研究所提出防止薄型BRB發生鋼管局部外突破壞之方法可供耐震設計應用。
The buckling restrained braces (BRBs) have gained wide acceptance in seismic buildings around the world. However, in order to increase the usable floor space in the building, the development of thin BRB (nBRB) may be warranted. The flexural buckling and the local bulging may occur when the thickness of the BRB’s restraining unit is reduced. The procedures of computing the bulging force and the resistance of the steel casing must be established before the nBRBs can be reliably used. The seismic resisting performance and the design methods of nBRBs are the priority of this research. When the nBRB using a flat core plate is subjected to a large compression strain, the high mode buckling wave will form. The wave crests would be in contact with the mortar and creating lateral forces on the mortar. The thickness and the strength of the mortar will help in spreading the lateral forces out into outward pushing forces act on the inner surface of the steel casing. If the lateral outward pushing force is greater than the resistance, the steel casing may bulge out locally. In this study, the contact force is estimated from the core plate high mode buckling wave length and the thickness of the unbonding material. The ABAQUS finite element analyses are performed to gain insights into the steel core plate high mode buckling and the lateral bulging force. The load path of the contact force and distribution of the lateral outward pushing force are investigated using ABAQUS models. The local bulging resistance is studied using plate limit analysis. A simple design procedure using the plate limit analysis to compute the strength of the steel casing is proposed. In this research, a total of eight nBRB component tests are conducted at NCREE using cyclic loading procedures. The proposed design methods predict the local bulging failure of steel casings in four specimens after the core stains exceeded 0.03. Research results confirm that under compressive strains greater than 0.03, the nBRB core high mode buckle wave length is about 8 to 10 times the core plate thickness. It is observed from the ABAQUS analyses that the bulging force spreads out through the contact line and distributes into the steel casing inner surface from a 45 degree angle in the longitudinal directions of the nBRB. The observed failure pattern of the steel casing and the extend of the lateral outward pushing force well agree with the analytical model. The test results confirm that the proposed design methods can be reliably applied for the seismic design of nBRBs to prevent the local bulging failure of steel casing.
為了持續優化網站功能與使用者體驗,本網站將Cookies分析技術用於網站營運、分析和個人化服務之目的。
若您繼續瀏覽本網站,即表示您同意本網站使用Cookies。