Investigation On Dynamic Characteristics And Instability Of Special-shaped Arch Bridges

Characterized by its novel and beautiful configuration, the special-shaped arch bridge has been widely employed as a structural type in small- and middle-span bridges, especially in urban bridges. However, because of its complex structural behaviors, dynamic characteristics and structural instability are always the main concerns for bridge design and construction. Focusing on the Liuyehu special-shaped arch bridge in Changde, Hunan Province, this paper carried out comparative analysis on bridge dynamics and instability, followed by structural parameter studies. The main studies and results are as follows.The structural features and development of arch bridges were introduced, and the main information about the Liuyehu Bridge was presented. The basic theories and methods about the structural dynamics and instability analysis were also introduced.The FEM model of the Liuyehu Bridge was estabilished in software ANSYS, and its first ten modals were obtained. Its frequencies and corresponding vibration shapes were compared to the results computed by the software MIDAS CIVIL, which confirmed the results and methods. It is found that the first modal is characterized by the arch lateral vibration, with its frequency significantly lower than both the arch and girder’s vertical vibration modal, which indicates that the arch lateral stiffness is the smallest. The study also found that the torsional modal is of lower frequency, which implies that the main girder has a small height and small height-to-width ratio.The instability analysis had been carried out based on the bridge FEM model both in ANSYS and MIDAS CIVIL, and the first five instability modals were presented and compared, with only small difference among the two softwares. The first instability modal with value of 29.4, is characterized by the arch lateral instability, which farther demonstrated that the arch lateral stiffness is the smallest.Since this value is significantly higher than bridge engineering practice, the structural stability of the Liuyehu Bridge is guaranteed.Considering several key parameters with major effects on bridge dynamics and instability, the corresponding results were obtained based on FEM analysis. After their influences were evaluated, the important structural parameters on bridge dynamics and instability were defined.The structural dynamic characteristics and instability results presented in thispaper will provide important guidelines and considerations for the design and construction of the Liuyehu special-shaped arch bridge.