台灣由於地狹人稠，土地資源有限，尤其在都市地區人口眾多且地價昂貴，許多建築物紛紛往高空發展，為了增加結構物的穩定性，樁基礎的使用也越來越多。又臺灣地屬於環太平洋火山地震帶西側為易發生地震的地區，故研究樁基礎的受振反應對安全上有一定的重要性。本研究利用離心模型試驗的尺度定律，進行80倍重力場的離心模型縮尺，模擬樁基礎埋置於乾砂土層中，受地震力作用的樁身反應，在此原則下設計並建造樁基礎的縮尺模型。配置具有三種不同上部結構物(L-Pile、M-Pile及S-Pile)，並輸入預定的振動事件。為探討樁基礎的受振行為，必須取得土壤及樁基礎的動態參數，於樁基礎模型及周圍的土層中裝設各型的感測器陣列，瞭解樁基礎及土壤受振過程加速度歷時，同時在受振過程中，利用應變計量測樁體在不同深度及不同瞬時之樁身彎矩，求取樁身沿深度的剪力、土壤反力與變位，藉此分析樁身因受土壤反覆作用力下之變位分析。其中，樁基礎S-Pile即檢視上部結構物之貢獻大小，藉由試驗結果探討樁基礎的受振反應。 結果顯示，基樁受振時，L-Pile與M-Pile之最大彎矩量皆發生在土表下1.6 m (z/Dp=1.26) 處，而無上部載重之樁基礎S-Pile則分佈於土表下4.8 m~14.4 m (z/Dp=3.8~11.3) 處。當樁基礎其系統主頻與地震頻率相近時會發生共振效應，彎矩最大值發生於第7~10個週數，而系統主頻與地震頻率相差較遠時，彎矩最大值發生在第1~3個週數且為負彎矩；S-Pile易受到土壤變位影響，彎矩最大值較無規律。M-Pile (27.6 m) 及S-Pile (25.2 m) 有無樁頭載重(133 ton)的條件下，S-Pile的樁身彎矩僅M-Pile的10%；L-Pile (35.4 m)與M-Pile (27.6 m)具相同載重，當上部結構重心較高時，低頻地震產生的樁身彎矩比高頻地震大，重心較低則反之。從土壤側向變位可知，S-Pile樁身彎矩與土壤變位有關；藉地表樁身彎矩可知，L-Pile的地表樁身彎矩主要受牛頓運動定律(Newton’s law)影響；M-Pile的地表樁身彎矩主要受轉動慣量(moment of inertia)影響。 ;There is limited plate land but too much population in Taiwan, so the area and price of land at city is very expensive. Therefore, skyscraper were often built in recent year. Taiwan locates at the west side of the Circum-Pacific seismic zone, earthquakes often occur in this area. In order to increase the stability of the structure, the moment response of pile foundation is getting more important. Three kinds of piles (L-Pile, M-Pile and S-Pile) arranged for four centrifuge modeling tests which were performed in an artificial acceleration field of 80 g. The response of pile foundation were simulated by physical modeling and the seismic loadings were applied by centrifuge shaking table. The prototype pile foundation was scaled to design the model pile, and it is reduced to 1/80 times in dimension to the centrifuge model. Three accelerometer arrays were installed in the soil layer to measure the acceleration histories during shaking. The response of bending moments along the pile would be obtained from the attached strain gauges. The rotation angle and deflection of pile along depth can be calculated. Especially, the S-Pile which without upper structure to investigate the contribution from pile head loading. Test results show that the frequencies of L-pile (with 10.8 m height of upper structure and mass of 1330 kN), M-pile (with 2.8 m height of upper structure and mass of 1330 kN) and S-pile (without upper structure) are 0.65 Hz, 1.99 Hz and 2.23 Hz, respectively. The soil resistance increases with the increasing depth for all models. The maximum bending moments of L-pile and M-pile occurred at 1.6 m (z/Dp=1.26, D is the diameter of pile) underground surface, and there is almost no significant bending moment along S-pile (z/Dp=3.8~11.3); the bending moments of L-Pile, M-Pile and S-Pile caused by Newton’s law, moment of inertia and soil displacement, respectively (L-Pile>M-Pile, 0.1×M-Pile≥S-Pile).
