考量基礎沉陷、滑動及埋置之淺基礎橋柱受震反應分析

Analysis of Bridge Columns with Shallow Foundations under Seismic Loading Considering Foundation Settlement, Sliding, and Embedment

胡文獻(Wun-Sian Hu)

指導教授 ： 邱俊翔

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000630

摘要

本研究以數值軟體SAP2000發展淺基礎橋柱受震反應數值分析模式。首先擴展鄭怡文（2018）所發展之搖擺基礎受震反應模型，於基礎底部加入摩擦彈簧以考慮基礎受震滑動之行為，並探討無埋置基礎模型之受震特性。為模擬基礎埋置效應，進一步於基礎側面加入p-y彈簧，以模擬側向土壤反力。最後利用所發展之分析模型建立大尺度之淺基礎橋柱數值模型，且考慮基礎-土壤互制及橋柱非線性行為，並進行一系列參數分析研究及探討。
本研究所發展之淺基礎模型分別與Chiou et al. (2018)及Shirato et al. (2008)施作之振動台試驗進行驗證，結果顯示分析模型能掌握振動台試驗模型之加速度反應及其基礎的受震搖擺與滑動反應。對於基礎於埋置作用下，亦能模擬出基礎轉角與沉陷量降低之趨勢。
此分析模式之垂直分布彈簧的性質為重要的影響因素，會顯著影響結構之受震與基礎搖擺沉陷反應，其彈簧模式組成由非線性遲滯彈簧串聯於線性彈簧及線性阻尼器。採用垂直平鈑載重試驗之力-位移曲線的初始勁度予以設定線性彈簧勁度會嚴重低估基礎的沉陷反應，並且採用系統初始頻率估算阻尼係數會低估結構在受震過程中能量消散。
淺基礎橋柱參數分析的結果顯示，當橋柱高/基礎寬之比例因子(H/B)增加，搖擺行為越明顯，其中以基礎尺寸較橋柱高度的影響顯著。在相同強度地震作用下，近斷層地震輸入運動具破壞性，此係由於其具有速度脈衝之緣故。綜合探討觀察到基礎的傾斜方向與基礎最大轉角方向有高度相關性。中心回復率參數不能確保整體橋柱系統穩定，而基礎最大轉角、頂部最大側移、基礎殘餘轉角及頂部殘餘側移與基礎之最小接觸面積有直接相關性，因此基礎受震過程中之接觸面積適合作為評估淺基礎受震性能之指標。

關鍵字

淺基礎 ； 結構-基礎-土壤互制行為 ； 搖擺行為 ； 彈簧模型 ； 非線性動態分析

並列摘要

This study applies SAP2000 to develop a numerical analysis model for seismic response of bridge columns with shallow foundation, considering effects of foundation rocking, sliding, and embedment. The model is expanded from the model of rocking governed foundations developed by Jheng (2018), by adding frictional springs at the base of the foundation to consider the sliding behavior and p-y springs at the lateral wall of the foundation to reflect the lateral soil reactions due to foundation embedment. The model are verified by two series of 1g shaking table tests in literature. Finally, the developed model is used to establish a large-scale bridge column-footing numerical model to conduct a series of parameter analyses and investigation, considering the nonlinear behavior of foundation-soil interaction and column.
From the verification analyses for the shaking table tests conducted by Chiou et al. (2018) and Shirato et al. (2008), the developed model can capture the structure acceleration response and the foundation rocking and sliding responses under seismic loading. For the embedded foundations, the model can also simulate the tendency of the reduction of the foundation rotation and settlement from embedment.
The property of vertical distributed springs in the model is an important factor, which may significantly affect the structure's response, and foundation rocking and settlement responses. Each vertical spring is composed of a nonlinear hysteretic spring in series with a linear spring and linear dashpot. Using the initial stiffness of the plate pressure load-displacement curve for the stiffness of the linear springs will significantly underestimate the foundation settlement response. Using the initial frequency to estimate the damping coefficient of the dashpot will underestimate energy dissipation.
The results of parametric analyses show that as the ratio of column height to foundation width (H/B) increases, the rocking response will be more pronounced, in which the influence of foundation width is more significant. It is observed the direction of the foundation permanent tilt is highly related to the direction of maximum foundation rotation. From the relationship between the minimum contact area and the maximum rotation, the maximum drift ratio, the residual rotation, and the residual drift ratio, it can be found that the rocking foundation design should be directed toward controlling the contact area.

並列關鍵字

Shallow foundations ； Structure-foundation-soil interaction ； Rocking foundations ； Winkler-spring model ； Nonlinear dynamic analysis

參考文獻

1.邱俊翔、柯永彥、黃俊鴻、陳正興（2014），「剛性基腳之旋轉性能曲線與工程設計考量」，地工技術，第132期，頁7-14。

2.鄭怡文（2018），「淺基礎橋柱受震反應分析方法之探討」，碩士論文，國立台灣大學土木工程研究所，台灣台北。

3.AASHTO (2009). Guide Specifications for LRFD Seismic Bridge Design, American Association of State Highway and Transportation Officials, Washington, D.C.

4.American Petroleum Institute (API). (2005). Recommended practice for planning, designing, and constructing fixed offshore platforms-working stress design.

5.Antonellis, G., Gavras, A.G., Panagiotou, M., Kutter, B.L., Guerrini, G., Sander, A.C., and Fox, P.J. (2015). “Shake table test of large-scale bridge columns supported on rocking shallow foundations.” Journal of Geotechnical and Geoenvironmental Engineering, 141(5), 04015009.