淺基礎橋柱受震反應分析方法之探討

Analysis Models of Seismic Responses of Bridge Columns with Spread Footings

鄭怡文(Yi-Wun Jheng)

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(2018年)

https://doi.org/10.6342/NTU201803725

摘要

淺基礎橋梁受到強震作用時，橋柱可能會產生塑鉸，基礎也很可能因埋置深度淺而產生搖擺行為。當基礎產生搖擺行為時，在基礎柔度的影響及基礎彎矩強度的限制下，橋柱結構的受震反應會受到抑制，雖然透過此搖擺隔震效應可降低結構承受之地震力，但過度的基礎搖擺反應可能引致基礎旋轉量及結構位移增加，亦會使基礎產生不均勻沉陷，反而對結構的使用性及安全性產生不利的影響。因此，欲合理評估淺基礎橋梁結構之耐震性能，應發展適當之分析模式以反映橋柱之非線性撓曲行為以及基礎因搖擺而產生之沉陷反應。
基此，本研究應用國震中心曾進行之大尺度淺基礎橋柱擬動態試驗及1g淺基礎橋柱模型振動台試驗資料，利用SAP2000程式對試驗進行模擬分析，發展可同時考量橋柱非線性撓曲行為及基礎搖擺效應之淺基礎橋梁受震反應分析模式。模擬比較分析結果建議採用非線性橋柱模型(梁元素加上塑鉸)搭配非線性基礎模型(非線性純受壓分布彈簧模式)可合理模擬試驗之結構與基礎反應。進一步採用所發展之分析模式進行參數研究探討基礎尺寸、地動特性及地震強度之影響，分析結果顯示，小基礎尺寸之橋柱塑性發展與頂部承受之加速度皆較大基礎尺寸低，不過會造成較大的上部結構永久位移和基礎永久沉陷；在相同地震強度下，近斷層地動相較於一般地震對結構物造成較大程度的破壞；在同一頻率特性之地震下，隨著地動強度上升，基礎與結構加速度及位移反應隨之上升。

關鍵字

淺基礎 ； 搖擺行為 ； 彈簧模式 ； 阻尼模式 ； 非線性動態分析

並列摘要

When a bridge with shallow foundations is subjected to a strong earthquake, the bridge columns may have nonlinear responses due to plastic hinging at the base, and on the other hand the foundations may rock due to shallow embedded depth. The rocking behavior can reduce the seismic force, which will help reduce the seismic demand on the foundation and further reduce the designed size of the foundation. However, the excessive foundation rocking may cause harmful structure displacement, foundation rotation, and foundation settlement to structure performance and safety. There is a need to develop an appropriate analysis model to evaluate the actual seismic response of bridge structures, accounting for the responses of both the structure and foundation.
To this end, utilizing the data of pseudo dynamic tests on large-scale pier columns with shallow foundations and lg shaking table tests on a bridge column-footing model conducted at the National Center for Research on Earthquake Engineering of Taiwan (NCREE), this study carries out a series of comparison analyses to investigate the applicability of numerical models to analyze the seismic response of bridge columns with shallow foundations considering the nonlinear flexural behavior of the column and the foundation uplift. The results show that a nonlinear column model (beam elements with plastic hinges), together with a foundation model using distributed nonlinear compression-only springs can reasonably predict the foundation and structure responses.
Based on the proposed model, parameter analyses are performed to investigate the influences of the foundation size, and the characteristics and intensity of strong motions. The analysis results show that because the rocking behavior is significant for the small foundation the plastic response of the column and the acceleration at the top of the column for the small foundation size are lower than for the large foundation size, but the residual displacement of structure and the permanent foundation settlement are larger for the small foundation size; the near-fault ground motions may result in a larger foundation response and larger damage to the structure; the larger the excitation intensity the larger the displacement and acceleration responses of the foundation and structure.

並列關鍵字

shallow foundations ； rocking behavior ； spring model ； damping model ； nonlinear dynamic analysis

參考文獻

[1] 內政部（2001），「建築物基礎構造設計規範」。

[2] 交通部（2009），「公路橋樑耐震設計規範」。

[3] 日本道路協會（2002），「道路橋示方書同解說-IV下部構造編」。

[4] 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。

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