ABSTRACT
Seismic design based on structural safety is crucial to the whole design process of bridges, especially when the bridge is located in meizoseismal area. For different earthquakes and structure fortifications, these seismic design strategies, such as changing the bridge system or structural style, will reduce the seismic demand in the weak region of bridges or improve the ability of capability-protected members. Asa special structure, self-anchored suspension bridge has been promoted and applied widely, while the research on seismic performance is still not enough. The current code only states basic principle on seismic design of self-anchored suspension bridge instead of detailed articles, which hinders the further application of this structure.
Based on the bridge seismic design process and structure safety strategies, seismic design of a selfanchored suspension bridge with arched tower is described in this paper. The superstructure of this bridge is steel-concrete hybrid girder with arched tower. The span of the bridge is 36 + 133 + 208 + 39 = 416 m. The substructure of this bridge is bored piles. Besides, the foundation soil of the engineering cite is silty clay, silt, sandy soil. In particular, the liquefaction phenomena should be considered in the seismic design process. The bridge site is located in seismic intensity 8 area According to the code, the design philosophy of this seismic design process is two-level fortification and two-stage design. By building several 3D finite element analysis models with different seismic design strategies, considering the pile-soil interaction and boundary effect of bridge approach, the result shows that the dominant factors of bridge seismic design are excessive seismic force of the tower bottom in the transverse direction and the displacement of bearing. Comparing the three seismic design strategies, by using isolation bearing, using viscous dampers and changing the loading path by setting up down cross-beam of pylon, it is concluded that the design strategy, which is based on seismic isolation system and changing the loading path on the tower, can achieve better result for improving the seismic demand under the premise that the section of the tower bottom remains the same.
At the last part of this paper, further research has been conducted on the seismic design strategy by using viscous dampers. In order to decrease the displacement of bearing and the seismic responses of tower, parameters of dampers are optimized. Result shows that the displacement of the girder is reduced when the damping coefficient is between 3000 and 5000 kN • (s/m) and velocity index is between 0.2 and 0.5, while the seismic responses of the tower under transverse excitation are not sensitivity to the damping coefficient and velocity index.
