不規則地震基盤對地表地震動的影響

從過去的大地震災害中可以發現，場址效應有可能會使得距離數十公尺左右的兩地點的地震動特性有很大的不同，也常常是造成某一區域的災害特別嚴重的主因，因此場址效應的問題成為工程地震學的重要研究課題。本研究的目的在使用我們自行發展的二維分析程式NONLIQUE2D，進行大量的參數研究，探討土層底部不規則岩盤對地表地震動特性的影響。　　研究的結果顯示，可以發現在同一地震作用之下，地表的地震動特性受到底部岩盤形狀的影響很大。而對同一形狀的地底岩盤而言，於不同強度的地震作用下，同一場址會有不同的反應，有時候的差異很大。位於不規則岩盤地表的加速度反應譜，在在弱震作用下，二維分析與一維分析之結果會因岩盤的形狀而互有大小；但是在強震作用時，則不論岩盤形狀為何，一維分析的結果遠小於二維分析的結果，表明在強震作用下，一維分析的結果相當不保守。此外，在鑽探間距的影響的分析中，本研究是以一對稱且岩盤邊坡無缺口之凹地來做模擬分析，本文建議鑽探間距以240公尺左右為最適合。

關鍵字

加速度反應譜；不規則岩盤；場址效應；有限元素法

並列摘要

From the past observations and theoretical studies, it can be found that the characteristics of the surface ground motion are significantly different for places of tens of meters apart as a result of site effect, leading to different degrees of damages. Thus, the site effect is an important issue for the earthquake engineering. The purpose of this study is to investigate the effects of irregular seismic bedrock on the surface ground motions using the program NONLIQUE2D. The analysis results show that the configuration of seismic bedrock significantly affects the characteristics of surface ground motion at different surface locations for an earthquake. For a given configuration of seismic bedrock, the site response changes depending on the intensity of earthquake. Regardless the shapes of irregular seismic bedrock, the surface acceleration spectra obtained from 2D analysis are always larger than that obtained from 1D analysis for a strong earthquake, indicating that 1D analysis is unconservative. In addition, a symmetric convex seismic bedrock model is adopted to investigate the effect of the drilling interval and to find its critical value beyond which the shape of seismic bedrock obtained from drilling data would affect the analysis results significantly. An interval of 240 m at most is suggested in this study for modeling the shape of seismic bedrock.

並列關鍵字

site effect ； irregular seismic bedrock ； finite element method ； acceleration spectra

參考文獻

21.王郁琛，「土層模式對地盤改良區域建築物受震反應之影響」，碩士論文，國立中央大學土木工程學系，中壢，民國九十五年七月。

18.張吉佐，「土層地工參數訂定方法彙整與檢討」，中興工程顧問股份有限公司大地工程部，民國八十七年，四月。

2.Sanchez-Sesma, F., Chavez-Perez, S., Suarez, M., Bravo, M.A., and Perez-Rocha, L.E., “The Mexico Earthquake of September 19, 1985-On the Seismic Response of the Valley of Mexico,”Earthquake Spectra, Vol.4, No.3, pp.569-589, 1988.

3.Bard, P.-Y., Eeri, M., Campillo, M., Chavez-Garcia, F.J. and Sanchez-Sesma, F.,“The Mexico Earthquake of September 19, 1985-A theoretical Investigation of Large-and Small-Scale Amplification Effects in Mexico City Valley,”Earthquake Spectra, Vol.4, No.3, pp.609-633, 1988.

8.Rassem, M., Ghobarah, A., and Heidebrecht A.C.,“Engineering Perspective for the Seismic Site Response of Alluvial Valleys,”Earthquake Engineering and Structural Dynamics, Vol.26, pp.477-493, 1997.

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不規則地震基盤對地表地震動的影響

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