- 學位論文
利用垂直陣列進行非線性地動分析之驗證
Verification of Nonlinear Ground Response Analysis by Vertical Arrays
摘要
台灣位於歐亞板塊與菲律賓海板塊相接所形成的環太平洋地震帶上，地震發生率高，雖然地震至今仍無法確實預測，但處在地震活動頻繁的臺灣，我們應針對地震防災進行研究與規劃，達成地震來臨時將其造成的危害減到最低的目的。要考量或分析地震問題必須先能預測與評估地震強度，地震強度的預測可分成兩類：(1)地動預測公式(2)理論地動反應分析；地動預測公式是採用統計方法回歸資料庫內大量的地震資料後所推估出來的經驗公式，主要用於推估地震強度的機率分布，例如以震度、震央距離與場址狀況來推估出尖峰地表加速度，而理論反應地動分析則是結合波動傳遞的數值模型發展出來的數值模擬方法。理論地動反應分析包含了有限維度的土壤模型與土壤的動態性質，分析的土壤性質模型可為等線性或是非線性。在工程方面，雖然因等線性分析所需輸入的參數較容易決定的關係使得等線性分析的應用較為廣泛，但當土壤處於大應變使得非線性行為明顯的情況下，非線性分析卻能比等線性分析更準確地預測地動反應的特性。 本研究以垂直陣列進行非線性地動分析之研究，我們發現以微地動做為輸入地動的情況下由等線性分析與非線性分析所獲得的地動預測差異並不大。此外我們也研究了兩種分析模式下剪力波速變異性對於地動分析的影響，研究後發覺可靠度方法中的一次二階(First Order Second Moment Method)方法會低估剪力波速的變異性所造成地動分析的不確定性，如要考慮剪力波速的變異性造成地動分析的不確定性的話建議由隨機剪力波速法(此法由考慮了標準差與土層間相關係數的土層模型與速度統計模型發展而成)來考量其變異性。
並列摘要
Taiwan is a seismically active region. It is vital for engineers to design for earthquake-resistant buildings and evaluate the performance of existing natural and man-made structures under variety of earthquake scenarios. To perform the aforementioned design or evaluation, engineers must be able to predict the level of ground motion at the site of interest. In the field of geotechnical earthquake engineering, there are two ways to predict ground motions: (1) use of Ground Motion Prediction Equations (GMPEs); (2) theoretical ground response analyses. GMPEs are derived empirically through regression on a database of strong motion. GMPEs can be used to estimate the probabilistic distribution (in terms of median and standard deviation) of an intensity measure, such as peak ground acceleration, based on magnitude, site-source distance, site condition etc. On the other hand, ground response analysis consists of numerical modeling of wave propagation. The analysis would encompass a soil domain of limited dimension and take into account dynamic soil behavior. Soil material models in ground response analysis can be equivalent-linear and nonlinear. In engineering practice, equivalent-linear ground response analyses are more popular due to its ease in input parameter selection. However, nonlinear ground response analyses have the potential to better predict the ground response, especially under large-strain condition, because representation of soil behavior is more accurate. In this research, performance of nonlinear ground response analyses is evaluated with the use of vertical arrays. It is found that predicted surface response from equivalent-linear and nonlinear analyses is generally the same if weak input motion is used. Moreover, effect of variability of shear-wave velocity on ground motion prediction is studied. It is found that uncertainty of ground motion due to variability in velocity would be underestimated by the First Order Second Moment method, therefore one should use randomized velocity profiles (defined by a layering model and a statistical velocity model that considers standard deviation and correlation between layers) in the uncertainty estimation.
參考文獻
延伸閱讀
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