Research on Long-Term Deflection of Large-Span Prestressed Concrete Segmental Bridges Built by Cantilever Method in Taiwan

• Main Authors: Yung-Kuan Wang, 王詠寬
• Other Authors: Jenn-Chuan Chern
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/se29v3

碩士 === 國立臺灣大學 === 土木工程學研究所 === 106 === In recent years, the old bridges around the world, especially the prestressed concrete box bridges constructed by the cantilever method, are facing a serious problem. The vertical displacement obtained by long-term monitoring of the central hinge of the bridge far exceeds the range estimated by the initial design. The indeterminate structural system caused by the rigid connection of the new type of bridge is also unable to grasp the influence of concrete creep and shrinkage, and cannot grasp the deflection and internal stress in the bridge. Through monitoring data, it is found that the trend of long-term displacement of bridges will not gradually slow down and stabilize, but will continue to develop toward a fixed slope under logarithmic time coordinates. Excessive deflection will cause the vertical displacement of the central hinge and the difference in the slope of the hinge angle to be too large, causing the impact of the vehicle due to the subsidence, thus causing concerns about the serviceability and safety of the bridge, which may eventually shorten the service life. The requirements for earlier retrofit or eventual demolition of bridge will impose a major burden on the government and society. The reasons for the long-term deflection of the bridge are mainly attributable to the creep of the concrete, the differential shrinkage and differential creep of the box girder section, and the loss of prestress caused by creep and shrinkage. At present, the prediction formulas for concrete creep and shrinkage specifications in various countries are generally underestimated in the trend of concrete deformation for several decades. The characteristics of concrete materials in Taiwan are also different from those in foreign countries. It is not appropriate to directly adopt foreign prediction formulas. In addition, the local engineering community mostly uses the two-dimensional beam element model analysis, which cannot truly reflect the phenomenon that the drying creep and the drying shrinkage rates are different due to the thickness variation of the top and bottom plates and the webs. Therefore, this study applies different creep and shrinkage prediction formulas for concrete, including ACI 209R, CEB MC10, GL2000, Model B4 and locally developed Model B4-TW formulas, and Yuan-Shan Bridge of the national highway No. 1 is used for study. A three-dimensional finite element model, which can take account of the phenomenon of different shrinkage and creep rate caused by geometrical scale differences, was developed to evaluate the vertical displacement of the location at central hinge and the loss of prestressed force. Through the comparison between the analysis results and the monitoring data, the differences between the prediction formulas and the influence of the extension from the materials to the real structure are discussed, a long-term deformation analysis model for concrete bridges suitable for Taiwan is developed. In addition to the assessment of the safety of existing old bridges, it can also provide reference for future retrofit, decommissioning or alternative planning for bridges. For new bridge design, a complete method for analyzing the long-term deformation and assessment of the useful service life of concrete bridges was established. The method will enable the engineering community to more clearly grasp the long-term displacement trend of Taiwan''s concrete bridges and its prestressed losses, and to facilitate safety monitoring and evaluation, and timely corresponding strengthening measures to avoid disasters, and to extend the service life of concrete structure during the design and maintenance phase to achieve the sustainability.