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  • 學位論文

搖擺基礎受震行為之振動台模型試驗分析

Analysis of Shaking Table Tests on a Rocking Foundation Model

指導教授 : 葛宇甯
共同指導教授 : 邱俊翔

摘要


獨立基腳為最早和最簡單的基礎形式,給予上部結構側向力作用時,基腳將會承受彎矩而發生旋轉變位。當地震發生時,基礎受上部結構垂直力及慣性力作用下會產生搖擺行為(Rocking Behavior)。由前人的研究可以發現,基礎產生搖擺行為具有隔震效果,使得結構物的加速度反應會受到限制。不過雖然利用基礎搖擺的隔震特性設計基礎,可降低地震力,進而減少基礎的設計尺寸,但基礎搖擺可能引致土壤產生的塑性變形及較大的基礎變位,其影響程度需要進一步探討。 由於基礎在搖擺過程中,可能會造成基礎旋轉勁度的降低,進一步影響結構受震反應,為了探討搖擺基礎受震過程中系統動態特性的變化,本研究利用國震中心曾進行之單柱-基腳模型振動台試驗資料,透過系統識別分析方法求取系統的動態參數。基此,本研究利用試驗量測到之加速度訊號進行傳遞函數分析(Frequency Response Function)與時頻分析(Time-Frequency Analysis),並以ARMA模型進行系統識別藉以觀察模型受震過程中動態系統參數的變化。震動台試驗結果已顯示出基礎搖擺行為確實能夠降低結構物的加速度反應,在較大的輸入運動時,結構物的動態反應會受其容許彎矩值限制。經由系統識別結果可知,受震過程中,模型的轉動頻率隨著輸入加速度增加而降低,系統的等效阻尼則隨之上升;當模型進入自由振動的階段時,轉動頻率會回升而阻尼比下降。另比較系統識別所得之系統參數與試驗基礎彎矩-轉角之遲滯迴圈發現,線性彈簧加上阻尼比的ARMA模型在小震動下與試驗彎矩-轉角之遲滯迴圈接近,但在大震動下因ARMA模型並不能完全反應系統因基礎上揚的非線性反應,則有較大的差距。

並列摘要


Isolated footings are a commonly used foundation types on stiff ground. When lateral loads are applied to a superstructure with footings, the induced moment will make the footing produce rotations. Further, during an earthquake, the footing may have rocking response due to seismically induced lateral loading. Previous studies have shown that the foundation rocking could reduce the acceleration response of the structure, which is referred to rocking isolation. However, although foundation rocking could reduce earthquake loading and further the designed size of the footing, it is also necessary to investigate the influence due to the accompanying lager footing rotation and soil plasticity. Rocking behavior could reduce the rotational stiffness of the footing and further influence the response of the structure. In order to investigate the change of dynamic characteristics of rocking system during rocking, this study utilize system identification methods to analyze experimental data of shaking table tests of a rocking-dominant column-footing model which had been conducted at National Center for Research on Earthquake Engineering (NCREE). The short time system identification method as ARMA model is applied to analyze the change in dynamic properties of the structure and soil system. During the process of shaking, the predominant vibration frequency decreased with increasing shaking intensity, and it would go up again as the shaking intensity decreased. Besides, the evolution of the identified damping ratio is depending on the degradation behavior of the vibration frequency. The damping ratio increased as the vibration frequency decreased. Based on the comparisons between the system identification results and hysteretic moment rotation curves, the identified rotational stiffness and damping ratio are consistent with those obtained from the hysteresis curve for the cases with small excitation; the difference would be significant under large excitation due to the assumption that the ARMA model regards the nonlinear spring behavior as an equivalent linear spring model with viscous damping.

參考文獻


[7]. Chen, S.Y. (2006). The Evaluation of Parametric System Identification and Hilbert-Huang Transform in Soil Dynamic Characteristics. (Master), National Cheng Kung University. Available from Airiti AiritiLibrary database. (2006)
[35]. Lin, C.Y. (2005). preliminary study of application of system identification to estimate soil dynamic properties. (Master), National Cheng Kung University. Available from Airiti AiritiLibrary database. (2005)
[2]. Anastasopoulos, I., Gelagoti, F., Kourkoulis, R., & Gazetas, G. (2011). Simplified constitutive model for simulation of cyclic response of shallow foundations: validation against laboratory tests. Journal of Geotechnical and Geoenvironmental Engineering, 137(12), 1154-1168.
[3]. Anastasopoulos, I., Kourkoulis, R., Gelagoti, F., & Papadopoulos, E. (2012). Rocking response of SDOF systems on shallow improved sand: An experimental study. Soil Dynamics and Earthquake Engineering, 40, 15-33.
[4]. Antonellis, G., & Panagiotou, M. (2013). Seismic Response of Bridges with Rocking Foundations Compared to Fixed-Base Bridges at a Near-Fault Site. Journal of Bridge Engineering, 19(5), 04014007.

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