SAP軟體應用於預鑄節塊橋柱分析之可行性研究

Abstract

橋梁預鑄節塊工法是一結合預鑄產製及機械化吊裝的施工方式，其在生產上由於採預鑄方式製造，除了讓橋樑工程師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影響及加快建造的速度外，亦可同時確保橋樑應有的建造品質及降低橋樑使用年限間的維護費用與建造期間對週遭環境的衝擊。但由於此類橋柱之耐震能力及行為等尚處於研究階段，因此多使用於低地震威脅的地區，且如美國加州及台灣等屬於中高地震區之區域都沒有採用任何以預鑄節塊工法建造的橋柱。因此，為了解以預鑄節塊工法建造的橋柱在強震區之耐震行為，由台灣的國家地震工程研究中心(NCREE)與美國University of New York at Buffalo的地震相關工程研究中心(MCEER)共同建立合作研究計畫。 有鑑於此類橋柱之實際應用尚處於研究階段，且尚未有相關規範明確訂定此類橋柱之設計準則，為了在試驗開始進行之前即可事先了解此類橋柱之基本性質，本研究以上述計畫探討之後拉式預力鋼建預鑄節塊橋柱為對象，並以已開發之有限元素分析軟體SAP作為分析工具，發展出一套可評估此類橋柱之耐震能力及運動行為之模型，使吾人在進行各種尺寸、配置方式及外觀之預鑄橋柱試驗之前，可先行建立此橋柱之模型進行參數分析，預測各項參數調整對於模型整體表現的影響，並觀察其在地震作用下的行為反應。 分析結果顯示本研究所發展之純預力鋼建節塊橋柱有限元素分析模型，以適合之設計構想為出發點，依照實際橋柱試體之材料強度、斷面性質、各部元件以及幾何運動行為來建置模型，對於此類橋柱在反覆載重作用下之預測結果尚為良好，其節塊開口行為及開口幅度、橋柱曲率變化以及橋柱初始勁度等皆與試驗結果相當符合；惟純預力鋼腱節塊橋柱試體於反覆載重試驗過程中並無塑鉸產生，其消能能力乃藉由柱底節塊保護層混凝土之碎裂、鋼腱與套管間之磨擦以及節塊間相當微小之相對移動來提供，而依照SAP模型以非線性靜力分析之設定並無法模擬此消能行為，但可預測遲滯迴圈之包絡線(pushover curve)；若以SAP模型進行非線性動力歷時分析來模擬試體在擬動態試驗下之反應，可在SAP中指定模型之阻尼比，對於試體在擬動態試驗下所引致之消能行為之模擬結果相較於反覆載重試驗來說，遲滯迴圈較為飽滿，因此在後續研究中亦可考慮SAP模型以非線性動力歷時分析來模擬反覆載重試驗。另外本研究亦提出用來模擬具有消能鋼筋試體之模型，因對於節塊橋柱之潛在塑鉸區行為尚無法完全掌握，模型之塑絞不易定義，故在此採用簡易分析，利用非線性元件來模擬節塊間之消能鋼筋。

The use of the precast modular construction for bridge column is the way which combines the previous casting work in the factory and the mechanization method of fabrication. Due to the precast way of production, it allows bridge engineers to minimize accidents in the work zone, to reduce traffic disruptions, and to increase the speed of construction, while maintaining construction quality and minimizing the life-time cost and environment impact. Because the seismic resistance and behavior of this kind of column is still being studied, most of the applications, however, have been in low-seismicity regions. In particular, there hasn’t been any application of the segmental precast bridge column in moderate to high-seismicity regions such as the state of California in United States or Taiwan. In order to investigate the use of segmental precast bridge columns in high-seismicity regions, a cooperative research project is established between the National Center for Research on Earthquake Engineering (NCREE) in Taiwan and Multidisciplinary Center for Earthquake Engineering Research (MCEER) at University of New York at Buffalo in the United States. First considering the application of segmental precast bridge column is still under investigated, and no relative standards or codes provide the detail guideline to design this kind of column. In order to understand the basic properties of the column before the test begun, this research takes the post-tensioned segmental precast bridge column described previously as the object and uses the developed finite element analysis software ― SAP , to develop a model which can estimate the seismic capacity and mechanical behavior of the column. According to this model, before the beginning of segmental precast bridge column tests in different sizes, design ways and figures, we can establish the SAP model to run parametric analysis, predict the effect of parameter adjustment to the model performance, and observe the behavior of the column under seismicity. The analysis results show that the finite element model of post-tensioned segmental bridge column can predict its seismic behavior well under cyclic loading, like the opening behavior, opening amplitude, curvature distribution and the initial stiffness of the column. The analysis results match the test results well, if we establish the SAP model according to the material strength, section properties, column members and the mechanical behavior of the real column in test. During the cyclic loading test, no plastic hinge is developed in the post-tensioned segmental bridge column, and the hysteretic energy dissipation of the column comes from the crush and spalling of the base segment, the friction between the tendons and tubes, and the slight relative displacement between segments. However, the SAP model can’t simulate the hysteretic behavior of the column under cyclic loading by nonlinear static analysis, but can simulate the envelope of the hysteretic loop (pushover curve); if we use the SAP model to simulate the column behavior under pseudo dynamic test by nonlinear time history analysis, we can assign the damping ratio of the model, then the simulation of the hysteretic behavior under pseudo dynamic test is better then under cyclic loading test. According to this result, we might consider the possibility of using SAP model to simulate the segmental precast column under cyclic loading by nonlinear time history analysis. Besides this research also develop the model used to simulate the specimen with energy dissipation bars (ED bars). Because of the uncertainty of the potential plastic hinge zone of segmental bridge column, we use simple method to simulate the ED bars between segments by nonlinear link.