| Summary: | 碩士 === 國立成功大學 === 土木工程學系 === 107 === This study investigates the seismic response of a group pile foundation bridge model after scouring, which causes the foundation to be exposed during near-fault earthquakes. The test uses a Biaxial Shear Box and a Long stroke high-speed seismic simulation shaking table. The relative density of sand was about 50%. The specimen was a single pier structure supported by a 2 by 2 group. In total 1.2 tons of steel mass was placed on the top of the single column to simulate the superstructure of the bridge. The first modal period of the structure is about 0.5 seconds.
The scouring model fixed the specimen in the shear box and the model with a specified exposed length of pile foundation, as a ratio of pile diameter D, include no scour depth (0D) and 3 times scour depth (3D) and 6 times depth (6D). The experimental input white noise obtained the main period of the structure, and the structural response was obtained by three representative earthquakes. The test results were measured by acceleration gauge, displacement gauge and strain gauge, which were used to analysis the dynamic properties of the structure.
The results show that as the scour depth increases, the structural period has a tendency to increase. With the increase of scour depth, the maximum strain value of the bridge column will decrease, and the maximum strain value of pile will change position and transfer to another position. The maximum strain value will appear at the top of the pile or 3 to 12 times the diameter of the pile. The impact of the earthquake El Centro on the structure is larger than the near-fault earthquake TCU068, which is mainly related to the frequency content of the surface. Numerical analysis shows that the use of API soil springs and equivalent linear springs (Proposed) have good results in superstructure for near-fault earthquakes or general earthquakes.
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