- 學位論文
預鑄式節塊混凝土橋柱之耐震行為研究與應用
Research and Applications of Post-Tensioned Precast Segmental Concrete Bridge Columns for Seismic Regions
摘要
應用預鑄節塊橋柱工法來縮短橋梁建造時間的方式在歐美各國已逐漸受到重視，預鑄節塊橋柱工法除了可以降低施工期間的意外事件、免除施工期間對交通的中斷及加快建造的速度外，亦可同時確保應有的建造品質及降低橋梁使用年限間的維護費用與建造期間對週遭環境的衝擊。然而目前多數的應用案例大多出現在低地震威脅的地區，因此在過去幾年來本研究進行了許多的相關的預鑄節塊橋柱試驗，且經由實驗研究證明，預鑄節塊橋柱試驗結果符合預期的結果，也發現預鑄節塊的接頭行為即代表整體的行為反應，因此為了進一步瞭解節塊間接頭的行為，新發展出的高性能不鏽鋼鋼筋被使用於預鑄節塊橋柱接頭中以改善橋柱的服務性與施工性，而其優異的消能行為及延展性大大提升了橋柱整體的耐震行為。在多次的實驗觀察發現預鑄節塊橋柱不像傳統橋柱一樣會出現嚴重的撓曲破壞，大部分的變形集中在接頭的打開及旋轉。因此，提出了名為接頭握裹滑移法的方法來分析預鑄節塊橋柱的行為。而經過實驗與分析的比較發現所提出的方法可準確地預測出橋柱的行為。此外本研究亦提出一套簡化的數值模擬方法，利用多種元件的組合來模擬預鑄節塊橋柱的行為，因此可輕易應用於現有的分析軟體中並進行非線性動力分析。 之後更將預鑄節塊節塊橋柱應用於隔震設計，藉由隔震的方式延長橋梁週期因而達到降低上部結構所受到之地震力，如此不僅達到兼顧橋梁安全及快速建造的設計目標，更因為地震力的大幅的減低，橋柱受到破壞的機率降低，因而延長了橋柱的生命週期。對於隔震預鑄節塊橋柱而言，隔震支承在結構系統中提供額外的消能以降低位移，隔震器的位移量只要在設計位移範圍內，其不會產生破壞，但橋柱一旦進入非線性，位移越大破壞也越嚴重。然而預鑄節塊橋柱因其自我復位特性，就算有大非線性位移，損傷也比傳統橋柱小許多。因此節塊橋柱搭配隔震支承的好處在於即使隔震支承位移用盡，預鑄節塊橋柱還可變形到3%，損傷都還很小。換言之，此系統可容納很大的位移卻損失輕微，可自我復位。 預鑄節塊混凝土橋柱由於消能容量顯著低於傳統橋柱，在同地震擾動下，欲達到相同的韌性需求時，地震力折減係數需較傳統橋柱小。本研究利用單自由度非線性動力分析，以及36個國內外地震歷時，探討適用於預鑄節塊混凝土橋柱的地震力折減係數。分析過程中，傳統混凝土橋柱與預鑄節塊橋柱地震行為，分別以Takeda遲滯模型以及勁度衰減自我復位(SDSC)遲滯模型模擬。研究結果證實，為達相同韌性需求，預鑄節塊橋柱地震力折減係數需比傳統橋柱的折減係數小。增加消能容量或降低韌性需求，將使預鑄節塊橋柱的地震力折減係數趨近於傳統橋柱。根據SDSC模型與Takeda模型所得地震力折減係數的比例，以及現行規範地震力折減係數的公式，本研究提出預鑄節塊橋柱地震力折減係數的建議值。 最後整理一系列的研究結果提出一套適合純鋼腱預鑄節塊橋柱(C0 Series)以及具自動復位及消能行為之預鑄節塊橋柱(C5 Series)的設計流程。
並列摘要
Precast concrete bridge construction has been proved to be an efficient solution in accelerating bridge construction and minimizing traffic disruption. However, due to concerns with the seismic performance of such type of construction, its application in seismic regions is limited. Therefore, many experimental and analytical studies were conducted. From their results, the seismic behavior of precast segmental bridge column possessed excellent ductility capacity that was adequate for use in regions of high seismicity. In order to improve the serviceability and constructability, a new material named high performance (HP) steel reinforcing bar was applied into the joint of precast segmental bridge column as energy dissipation bar and the cyclic behavior of precast segmental concrete bridge columns with high performance (HP) steel reinforcing bars as energy dissipation (ED) bars were investigated. The HP steel reinforcing bars are characterized by higher strength, greater ductility, and superior corrosion resistance compared with the conventional steel reinforcing bars. Three large-scale columns were tested. One was designed with the HP ED bars and two with the conventional ED bars. The HP ED bars were fully bonded to the concrete. The conventional ED bars were fully bonded to the concrete for one column, whereas unbonded for a length to delay fracture of the bars and to increase ED for the other column. Test results showed that the column with the HP ED bars had greater drift capacity, higher lateral strength, and larger ED than that with fully bonded conventional ED bars. The column with unbonded conventional ED bars achieved the same drift capacity and similar ED capacity as that with the HP ED bars. All the three columns showed good self-centering capability with residual drifts not greater than 0.4% drift. An analytical model referred to as joint bar-slip rotation method for pushover analysis of segmental columns with ED bars is proposed. The model calculates joint rotation from the slip of the ED bars from two sides of the joint. Good agreement was found between analytical predictions and the envelope responses of the three columns In addition, in order to reduce the seismic demand of precast segmental bridge column, seismic isolation system was applied to precast segmental bridge column and a large scale experimental study was conducted. The test results showed that isolated precast segmental bridge column system can reduce the acceleration of superstructure effectively. Therefore, reducing the shear demand and avoiding the damage of substructure. The benefit of using isolated precast segmental bridge column is that even isolation displacement demand is more than its capacity, precast segmental bridge column can deform more than 3% drift without sever damage. In other words, isolated precast segmental bridge column system has a capacity of large deformation and self-centering. The energy dissipation capacity of precast segmental bridge column is smaller than that of traditional bridge column. Under the same earthquake excitation, the strength reduction factor for precast segmental bridge column should be smaller than that for traditional one to achieve the same ductility demand. In this study, nonlinear dynamic SDOF analysis was involved, and 36 different ground motions were used in this analysis to investigate the proper strength reduction factor for precast segmental bridge column. In the analysis, bilinear plastic (BP) hysteretic model and stiffness degrading self-centering (SDSC) hysteretic model were used to present the behavior of traditional bridge column and precast segmental one, respectively. According to the result, it was proved that the strength reduction factor of precast segmental bridge column is smaller than that for traditional one. The ratio of strength reduction factor for SDSC model with different energy dissipation capacity and different ductility demand to that for traditional one was meshed up to modify the strength reduction factor formula provided in current seismic design code. Finally, a rational design method was proposed and verified.