發展考量慣性力及地盤運動效應之樁基礎擬靜力分析方法

Development of Pseudo Static Analysis Method for Pile Foundations Considering Inertial and Ground Movement Effects

傅有為(Yu-Wei Fu)

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(2021年)

https://doi.org/10.6342/NTU202100957

摘要

本研究以數值軟體SAP2000發展考量慣性力及地盤運動效應之樁基礎擬靜力分析方法。首先改良李奕霆（2018）所發展之動態結構-樁-土互制模型，於土壤p-y彈簧中加入輻射阻尼係數，以考慮樁基礎受震時土壤之輻射消能行為，並利用楊宗翰（2016）之振動台試驗進行驗證，結果顯示所改良之動態分析模型能掌握振動台試驗模型之質量塊加速度反應、樁身彎矩反應以及地盤之加速度反應。進一步以此動力分析模型為基礎發展考量慣性力及地盤運動效應之樁基礎擬靜力分析方法，最後再應用所發展之方法於實際地震情況，針對不同樁出露地表長度、地動特性與樁身勁度進行一系列參數分析。
本研究所發展之擬靜力分析方法包含慣性力與地盤位移兩部分。利用容量震譜法，決定結構受震之最大加速度，慣性力由最大加速度乘上樁頭質量得出，施加於樁頭上，以模擬慣性力之效應；地盤位移可透過地盤反應分析得到之最大地盤位移，將其施加於樁-土p-y彈簧，以模擬地盤位移之效應。然而實際受震時，慣性力與地盤位移不一定會同時達到最大值，藉由探討慣性力-地盤運動間相位關係，提出慣性力/地盤位移參與因子隨正規化頻率之分佈，由此分佈對慣性力與地盤位移進行修正。由於樁基礎受震屬於多輸入源之情況，本研究以權矩陣的概念考慮地盤各深度運動對於樁基礎之影響，利用加權運動取代基盤運動作為擬靜力分析之輸入源。
參數分析的結果顯示，在一般地震作用下，樁身彎矩反應主要受到慣性力控制，地盤位移之參與對彎矩反應影響並不顯著；而在近斷層地震作用下，樁除會受到慣性力顯著影響外，因地盤產生較大之變位，使得樁身也受到地盤位移之顯著影響，造成樁身深處也承受到不小的彎矩，地盤位移之大小會直接影響樁身深處的彎矩大小。

關鍵字

樁基礎 ； 結構-樁-土互制效應 ； 擬靜力分析 ； 慣性力 ； 地盤運動效應

並列摘要

This study uses SAP2000 to develop a pseudo static analysis method for the seismic response of a pile under earthquakes considering inertial loading from the structure and kinematic loading due to ground movement. First, the dynamic structure-pile-soil interaction model developed by Lee (2018) is improved by adding radiation damping coefficient in soil-pile interaction springs to consider energy dissipation behavior of piles under low-intensity earthquakes. The dynamic model is applied to simulate shaking table tests conducted by Yang (2016) to verify its applicability. Results show that the model can reasonably simulate the mass accelerations, pile bending moments, and ground accelerations in the tests. Then, based on the dynamic model and associated parametric analysis results, the pseudo static analysis method is developed. Finally, the method is applied to cases of actual earthquake histories, considering different pile exposed lengths, excitation motions, and pile stiffness.
The pseudo static method includes two parts: inertial and kinematic loadings. The capacity spectrum method is used to determine the maximum acceleration of a structure under seismic loading. The inertial loading is computed to be the maximum acceleration multiplied by the pile-head structure mass and applied at the pile head. Ground response analysis is used to determine the maximum ground displacement. And it is applied on the soil-pile interaction springs to simulate the kinematic loading from the ground movement. Since the effects of inertial and kinematic loadings may not reach their maxima at the same time, the participation factors of inertial loading and kinematic loading to their maxima in terms of the normalized frequency (excitation frequency divided by pile-soil system frequency) are built, by which the maximum inertial and kinematic loadings are modified. Since piles are subjected to multiple sources of excitation along the pile shaft, this study proposed a weighted motion to combine the contributions of different ground movements at different depths for the pseudo static method.
Parametric analysis results show that the bending moment response of the pile is mainly influenced by inertial loading under general earthquakes; however, under near-fault earthquakes, the pile is also significantly influenced by kinematic loading due to large ground displacement.

並列關鍵字

Pile foundation ； Structure-pile-soil interaction ； Pseudo static analysis ； Inertial force ； Ground movement

參考文獻

李奕霆（2018），「離心機振動台試驗樁土互制行為之數值分析」，國立臺灣大學碩士論文。

楊宗翰（2016），「具不同上部結構之樁基礎受振行為」，國立中央大學碩士論文。

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