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標題: 動態參數於結構構件挫屈載重之測定分析
Determination of the Buckling Load of Structural Element Using Vibratory Data
作者: 劉正達
Liou, Cheng Dar
關鍵字: buckling load
vibratory data
natural frequency
mode shape
出版社: 土木工程學系
摘要: 摘 要 挫屈(Buckling)現象為結構系統或構件,承受壓力作用到達某一臨界點時,對外力作用失去抵抗能力而呈中性平衡之現象,此現象並不造成結構材料之破壞,但其對外力失去抵抗作用而可能產生之大量變位,將造成構件失去穩定性而側潰。故壓力構件挫屈現象之發生並不單由應力達到某一材料強度而產生,係受到多種因素的影響,包括構件尺寸、邊界束制條件、構件材料性質等,而構件尺寸及材料性質較為容易掌握,邊界束制情況則因工程技術上的困難,邊界接頭部份處理難以完美,較難達到設計要求,使壓力構件之挫屈載重與理論值有相當的出入,為了整體結構之穩定性考量,於實務設計上常採用較大的安全係數,因此往往造成設計上的過於保守及材料的浪費。為了實務設計的需要,發展一套非破壞的試驗方式,以分析壓力構件之挫屈載重實有其必要性。 現今,由於量測技術之高度發展,結構構件之動態參數可由模態分析方法準確求得,因此本文建議於結構構件之挫屈載重量測方法,可由結構構件之振動參數,即自然振動頻率及振型求取影響函數,再以力法之觀念求取結構構件之挫屈載重,本文所建議之方法適用於柱、初始彎曲桿件、平版、以及薄壁樑等結構構件,並且可同時求得初始彎曲桿件之載重-變位圖。整個試驗分析過程不用施加軸力及預知材料性質,並且適用於各種邊界束制條件。
ABSTRACT Buckling is one of the major causes of failure in structures, and therefore the possibility of buckling should always be considered in design. In design analysis, the assumed conditions are usually made in advance and then the buckling load was derived. However, in engineering work, the structural integrity is often not as reliable as expected due to the immaturity of current engineering techniques. Thus the actual load response for a structural member is sometimes not consistent with that of design predictions. For design considerations, it is necessary to establish an analytical method for determining the buckling load of structural member experimentally. In this paper, a nondestructive testing approach using dynamical characteristics of natural frequencies and vibration mode shapes for predicting the buckling loads of structures such as imperfection columns, flat plates, and thin-walled beam is proposed. This approach is also used to establish the load-deflection curve of the imperfect column. The proposed method does not require the application of axial load and is feasible for arbitrary types of boundary conditions. Several examples and discussion are included to illustrate the salient features and validity of it.
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