人工合成地震對基樁耐震性能之影響

The Influences of Artificial Earthquakes on Seismic Performance of Piles

劉佳泓(Chia-Hung Liu)

指導教授 ： 張德文

淡江大學/工學院/土木工程學系碩士班/碩士(2014年)

https://doi.org/10.6846/TKU.2014.00843

摘要

本研究以美國太平洋地震工程研究中心所建議的PBEE法探討樁基耐震性能特性，所採用的數值工具為一維EQWEAP分析，該分析係結合集中質塊法、砂土孔隙水壓模式、黏土簡易模式及波動方程式方法等研發而成。所考慮的人工地震生成法包括：a. 以目標PGA為主的加速度歷時紀錄縮放法、b. 以建物耐震設計規範反應譜配合現場地震加速譜所生成的人工地震、以及 c.考量特定地震規模和震央距所模擬的律定性地震。研究比校不同方法所生成地震對特定地盤和該地盤內的樁基礎反應影響，所考慮的地震分為中小地震、設計地震和最大考量地震，除建築物耐震設計規範所規定者，研究同時採用鄭錦桐(2002)所建議之台灣各地危害度曲線比較目標PGA差別。除地盤的非線性行為外，基樁的非線性行為和破壞容量亦屬重要，本研究係以LPILE程式推算基樁彎矩容量，界定性能狀態標準，以討論不同耐震性能目標下樁身最大位移和彎矩影響。

研究結果顯示：上述分析可充分瞭解樁基在地震下行為，包括：基樁反應、不同地震等級下之基樁位移和彎矩性能，進而做為評估其耐震性能使用。研究以台北新莊地區之快速道路橋梁樁基礎為例，以不同方式生成人工地震歷時，配合不同作用力型式分析出數值模型的耐震性能及相關參數影響，研究發現：若以動態方式模擬上構水平慣性力時，在設計地震下(PGA=0.24g)，Kaul法和縮放法最大位移比值介於1.4~1.9，最大彎矩比值介於0.8~1.4；在最大考量地震下(PGA=0.32g)，Kaul法和縮放法最大位移比值介於1.03~2.44，最大彎矩比值介於0.5~2.9。若就基樁性能而言，在動態力作用下，案例之樁基礎在中小度地震下皆保持彈性，在設計及最大考量地震下樁基礎僅有少數案例會達到降伏狀態；若以靜態方式模擬上構慣性力，則分析將過於保守，破壞將集中於樁頂。研究同時發現，若以鄭錦桐(2002)所建議危害度曲線之目標加速度(設計地震0.29g、最大考量地震0.51g)進行模擬，樁的變形量將增加，但數值模型在動態力作用下尚能滿足耐震性能要求。不同地震生成方法對有限度的地震分析影響將很有限。

關鍵字

人工合成地震 ； 樁基礎 ； 波動方程 ； 樁受震行為 ； 性能分析

並列摘要

This study intends to discuss the applications of probability analysis on seismic performance of piles with the one-dimensional wave-equation modeling. Numerical examples were conducted for typical pile foundations on a bridged expressway located at Sinjhuang District in New Taipei City. Piles of 2m in diameter and 60m in length were studied. From the local seismic hazard curves, peak ground accelerations at the moderate, the design and the maximum consideration earthquakes were targeted, and the seismic records were created based on the significance of past quakes. Nonlinear moment-curvature relation of the concrete pile was used to simulate the damages and failure of the piles. At Artificial Earthquakes, this study considered three methods including: a. Scaling Method, b. Kaul Method, and c. the point source stochastic simulations. Not only the PGA suggested by the seismic design code for buildings but also those proposed by Cheng (2002) on seismic hazard curves of Taiwan were studied. The nonlinearities of the piles were modeled based on trilinear moment-curvature relationships of the concrete pile. The moment capacities of th e pile were obtained from LPILE analysis.

The result of study reveals: When pile foundation behavior under different earthquakes, it is found that under the design earthquake (PGA=0.24g), the maximum ratio of the pile displacement from using Kaul law and scale law is on the order of 1.4~1.9, the ratio of the maximum pile moment is between 0.8~1.4; for the maximum consideration earthquake (PGA =0.32g), the maximum ratio of the pile displacement from Kaul law and scale law is about 1.03~2.44, the ratio of the maximum bending moment is in the range of 0.5~2.9. As to the pile performance, if the horizontal load from the superstructure was time-dependent, then the piles would remain elastic for moderate earthquakes. In a few cases of design and maximum consideration quakes, the piles would be slightly damaged with the cracks. However if the static loads from the superstructure were taken, then the assessment would become over-conservative. Severe damages would occur at the pile head. The target PGA is also critical to the results. Different target PGAs will certainly provide various estimations. As the reults, the study finds that the methods to produce artificial earthquakes are not that sensitive if the target PGA was limited to some extent.

並列關鍵字

Artificial Earthquake ； EQWEAP ； pile foundation ； wave equation analysis ； damage model ； equivalent foundation stiffness ； seismic performance

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