- 學位論文
初始幾何缺陷對具深寬翼鋼柱之特殊抗彎矩構架其耐震崩塌性能之影響
Influence of geometric initial imperfection on seismic collapse capacity of steel special moment frames with deep columns
摘要
熱軋寬翼型鋼由於軋制、運輸及安裝過程等影響，必定會存在初始變形，而於有限元素分析中，傳統上多利用挫曲模態疊加之方式來模擬構件之初始幾何缺陷。然而，以此規律性之變形模擬具隨機性之初始幾何缺陷之合理性，以及初始幾何缺陷對熱軋深寬翼鋼柱之耐震能力、或特殊抗彎矩構架之崩塌性能之影響，卻仍無詳細之研究或探討。 本研究先以三維雷射掃描儀量測十四根熱軋寬翼型鋼之輪廓，之後以二維功率譜法分析量測所得之初始缺陷，以及提出可用於模擬寬翼型鋼初始幾何缺陷之數值模型。最後以有限元素法，將提出之二維功率譜法以及傳統採用之模態疊加法所建立之初始幾何缺陷施加於具有深寬翼鋼柱之特殊抗彎矩構架，以進行構架之崩塌易損性分析，並量化初始幾何缺陷對構架耐震崩塌性能之影響。 模擬結果顯示，初始幾何缺陷雖可改變深鋼柱之挫曲行為甚或抗彎矩構架之崩塌模式，其對抗彎矩構架崩塌行為之影響並無一致性，並與其本身大小及方向、地震歷時之選取、以及完美構架(無缺陷)之柱挫曲變形及崩塌模式等因素相關。對具小軸力之四層樓構架，初始幾何缺陷因構架在不同地震歷時下之崩塌模式不同，對崩塌性能之平均影響並不顯著。而對八層樓構架及具大軸力之四層樓構架，因鋼柱於不同地震歷時下之挫曲行為較一致，初始幾何缺陷對構架崩塌性能之影響較為明顯，但平均而言，其影響於工程應用上仍落於可接受之誤差範圍內。此外，因施加之大小與方向不同，初始幾何缺陷亦可能提升構架崩塌性能，導致較不保守之評估結果。 由於使用高精度及高擬真之有限元素模型模擬結構於大變形下之反覆載重行為時，構件在加載初期即可生成幾何缺陷，並於無施加初始幾何缺陷時適當模擬其行為。因此，對於本研究所考慮之僅於周緣具有特殊抗彎矩構架、且採用深寬翼鋼柱之鋼構建築物，若以高精度、高擬真之有限元素模型探討其耐震崩塌行為時，建議忽略初始幾何缺陷之影響，以避免事先決定之挫曲模態導致不保守之結果。
並列摘要
Hot-rolled, wide-flange (W-shape) steel members are known to have initial geometric imperfections (IGIs) due to fabrication, transportation, and installation. Traditionally, a superposition of buckling modes, i.e. modal approach, is used to simulate the IGIs in steel members in finite element analysis. However, the rationale for using a deterministic shape to simulate IGIs that are inherently random, and the effect of IGIs on seismic behavior of steel special moment frames (SMFs) with deep wide flange steel columns, have not yet been investigated. To address this shortcoming, this study employs a 3D noncontact laser scanning technique to measure the initial geometric of fourteen steel members with wide flange sections. A spectral approach is used to analyze the measured imperfections as a 2D field of random vibrations and propose modeling recommendation for IGIs. Various types of IGIs created by proposed spectral approach or traditional modal approach are applied to 4-story and 8-story prototype SMFs with deep steel columns to quantify the effect of IGIs on seismic collapse capacity of SMFs using finite element analysis. The simulation results show that even though IGIs can affect column buckling behavior and frame collapse mode under certain conditions, their effect on seismic collapse capacity of SFMs is generally small and inconsistent and greatly depends on their amplitudes and directions, selection of ground motions, and collapse behavior of the perfect SMF. For the 4-story SMF under small gravity loads, the effect of IGIs on seismic collapse capacity is insignificant because of different collapse modes under selected ground motions. Although the effect becomes more pronounced for the 8-story SMF and the 4-story frame under greater gravity loads due to consistent collapse modes, it can still be ignored for engineering applications on average. The effect can even be positive if the directions of applied IGIs and column buckling shapes are misaligned. As a result, for the steel buildings with perimeter special moment frames using deep steel columns, it is suggested that initial geometric imperfections need not be incorporated in high fidelity numerical models with high precision, which can generate their own IGIs when loaded and adequately capture nonlinear behavior of structures under large deformations, to avoid unconservative evaluation results.
參考文獻
延伸閱讀
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