樁基承載力與耐震性能之關聯性研究

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Title:	樁基承載力與耐震性能之關聯性研究
Other Titles:	Study on capacity and seismic performance of pile foundations
Authors:	宋士豪;Sung, Shih-Hao
Contributors:	淡江大學土木工程學系碩士班張德文
Keywords:	樁基礎;性能分析;承載力;樁受震行為;Performance Based Design;bearing capacity;seismic analysis;pile foundation
Date:	2012
Issue Date:	2013-04-13 11:47:55 (UTC+8)
Abstract:	國內現行土木設計規範對於地下結構物設計，多係以靜力設計概念做為主要考量，而受震反應上仍著重於上部結構物，但無論是地下或地上結構物，其受震時應具相當之影響。故本研究針對(地下結構物)樁基礎，以該設計要點(承載力)與性能設計法結合，藉兩者間之關聯性建議一樁基礎耐震性能設計流程。本研究案例係以台北盆地道路橋樑樁基礎為設計參考，其中樁基豎向及側向承載力係以APILE 5.0、LPILE 6.0程式，模擬樁載重試驗曲線（荷載與沉陷或荷載與變位關係曲線），並依樁載重試驗詮釋法中可能低估、最佳和高估之方法詮釋之，以了解單樁豎向及側向承載力之範圍，並配合可靠度分析-蒙地卡羅法，評估土壤及外力變異時，單樁所具備之使用效益；性能設計部份係以LPILE 6.0 分析各樁徑下，樁基礎之開裂、降伏及極限彎矩容量，且將各階段之彎矩容量結果加以迴歸之，建立各階段之容量迴歸曲線，並以此為耐震性能標準(耐震性能I，開裂彎矩；耐震性能Ⅱ，降伏彎矩；耐震性能Ⅲ，極限彎矩)；而實際受震反應則以地震再現周期30年、475年及2500年為地震考量，藉由EQWEAP程式分析樁基實際受震反應情形，並根據其實際彎矩產生之彎矩與前述三者彎矩容量階段加以判斷之，以了解各樁徑下基樁之耐震性能。研究結果顯示：(1)傳統承載力評估：各詮釋法比較結果相似於既往經驗，此外，增加樁長並無法有效提升樁基的側向承載力，基樁的側向承載力係以上部土層(<15m)為主而發揮。(2)彎矩容量：主要係由混凝土、鋼筋材料強度及鋼筋斷面積比（隨樁徑增加而鋼筋量提高）改變，當鋼筋比固定時，隨樁徑增加而彎矩容量會提升。(3)靜態承載力與耐震性能關聯性：本研究建議之耐震性能設計流程，設計者首先需進行樁基礎傳統靜力設計，決定樁基礎結構尺寸範圍(配置、樁徑和樁長)和細構設計(含配筋量以及彎矩與曲率關係)，接著藉由分析樁基實際之受震反應，即可判斷該樁設計下是否符合耐震性能條件。而應用於實際案例分析評估，其結果合理且具參考價值。　The existing civil engineering design specifications of the underground structures are mainly in static design-based. The seismic design concern is focusing on the influences of the superstructure and/or the seismic effects to the ground soils. None of these can reveal exactly how the underground structure behaves due seismic ground motions. This study will try to link the conventional bearing capacity calculations of the piles to the seismic performance of the pile on deformations, and a preliminary design process is suggested. Numerical models were established for a typical bridge pile foundation located in Sinjuang District of New Taipei City. The axial and lateral bearing capacities of the piles were simulated using APILE and LPILE programs and the major interpretation methods were adopted to identify the pile capacities. A reliability analysis using Monte Carlo simulation was conducted for vertical pile capacity. The pile moments at the occurrence of concrete crack, bar yield and plastic hinge were simulated using LPILE program. These moments are used for different levels of seismic design of 30, 475 and 2500 years return periods, respectively. The maximum bending moments of the piles were analyzed using EQWEAP analysis. Finally, the correlation between the capacities and the seismic performance of the piles was suggested.. 　　The observations are summarized as follows：(1) For estimations of the bearing capacity, the results found for Interpretation methods are similar to previous observations. Increasing the length of pile after a certain value (say 15m) will not increase the lateral capacity of the pile. (2) For capacity of the internal moment：The strength of concrete and steel as well as the steel bar sectional area will affect the moment capacity. If the steel bar area ratio is fixed, increasing the pile diameter will enlarge the pile capacity. (3) For correlation between bearing capacity and seismic performance：This study suggests a procedure to determine the seismic performance of the pile foundation. The designer needs to do the static design first, and then makes the assessments for the piles under the seismic conditions. Case studies showed that the proposed procedure is rational and can be applicable to seismic design for pile foundations.
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