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  • 學位論文

垂直地動地盤反應分析:標準分析基準之建立

Benchmarking of Vertical Ground Response Modeling Procedures

指導教授 : 郭安妮

摘要


臺灣地處於歐亞板塊及太平洋海板塊交界之東亞島弧地震帶上,故在進行地工設計或結構設計時,需要審慎考量及評估工址受震時之地盤反應對設計之影響,以確保結構體之耐震能力有達規範之要求,保障人民的生命財產安全,避免造成過大之經濟損失。在地震工程中,影響地動的因素相當複雜,但主要可以分為三項: 一、地震規模、震源深度和斷層破裂過程及形式的震源效應。二、地震波傳遞的路徑效應。三、地震波因局部地質土壤材料組成特性、土層剪力波速構造以及場址附近之地形變化所引起之場址效應。 在真實地震中會同時具有水平向以及垂直向之地面運動,這意味著,工址於地震期間不僅會受到水平的搖動也會受到垂直的震盪。但在過去幾十年間,研究著重於水平向運動之影響,而不考慮垂直向運動之影響。只有在重要結構物才會同時考慮水平以及垂直運動,比如說核電廠。而會忽略垂直向之影響主要是因為垂直向之幅度一般來說會比水平向之幅度來得小。然而在1994年的北嶺地震中,曾記錄到最大垂直地表加速度高達1.18g(m/sec^2);在1995年的阪神地震中,也有紀錄到最大垂直地表加速度是最大水平地表加速度的兩倍。根據Gülerce的研究,垂直向運動對橋梁的地盤反應分析也會有顯著的影響。 在本研究中,收集強地動觀測網井下陣列觀測站所記錄到之地震加速度歷時紀錄,並且進行相關儀器以及參數校正。獲得修正之加速度紀錄後,分別計算地表以及井下之反應譜以及傅立葉頻譜找出各測站之場址效應放大因子。本研究將井下之加速度紀錄視為輸入運動,利用了五種不同的數值模型進行一維垂直地盤反應分析(Deepsoil),並且將所得之預測結果和地表之反應譜和傅立葉頻譜進行比較。期許能夠找到適當之垂直地盤反應分析模式,以供耐震設計時參考。

並列摘要


To evaluate the effect of site condition on earthquake ground motion, ground response analysis is often performed to simulate the wave propagation process from an at-depth location to the ground surface. Detailed site condition, such as stratigraphy, geometry and soil properties, may be incorporated. However, these analyses are often performed for the horizontal ground motions. In the earthquake engineering practice, there is no consensus on how to perform ground response analyses to estimate the waveforms for the vertical component of the ground motions. In this research program, a comprehensive comparison between different ground motion modeling methods of estimating vertical ground motions would be performed. Differences between the predictions of each method would be systematically evaluated. The objective of this study is to provide clear guidelines on estimating vertical ground motions using numerical ground response analysis and to estimate the bias associated with the simplified approach (which can be incorporated into the prediction if such approach is used). In this study, vertical site response analyses were performed for the vertical arrays in Taiwan. Using the downhole recordings as the input motions, predictions for the surface vertical response spectra were obtained using five ground response modeling procedures. By comparing the predictions to the recordings, it is found that there are biases (significant overestimates) in the predicted spectra for periods less than 1 second. Correction factors for reducing the prediction biases are recommended.

參考文獻


[1] Bozorgnia, Y. and Campbell, K. W., (2013), Ground Motion Model for the Vertical Component of PGA, PGV, and Pseudo-Acceleration Response Spectra, NGA-West2 Ground Motion Prediction Equations for Vertical Ground Motions, 85-123.
[2] Beresnev, I. A., Nightengale, A. and Silva, W. J. (2002), Properties of vertical ground motions, the Seismological Society of America, Vol. 92, No. 8, 3152–3164.
[3] Elgamal, A. and He, L. (2004), Vertical earthquake ground motion records: an overview, Journal of Earthquake Engineering, Vol. 8, No. 5, 663–697.
[4] Kontoe, S., Christopoulos, A. and May, R. (2013), Site response analysis for vertical ground motion, 4th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering.
[5] Kramer, S. L., (1996), Geotechnical Earthquake Engineering, Prentice Hall, Upper Saddle River, New Jersey, 254-280.

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