Study On The Dynamic Response And Nonlinear Damage Feature Of Group-piles Foundation In Deep-water Bridges Excited By Strong Earthquakes

Group-piles foundation is a common form for the substructure of deep-water bridges, and are also the vulnerable and weak part under earthquake. Since the dynamic property and dynamic response of bridges under earthquake will be affected by water, hydrodynamic effect should be highly considered in seismic design of deep-water bridges. Based on potential-based fluid theory and method, the elastic and nonlinear group-piles foundation models taking structure-hydrodynamic coupling effect into consideration from a typical deep-water bridge were established, the effectiveness of the Morison equation and the simplified formula used to calculate the hydrodynamic effect was tested in this paper. And then, the dynamic response feature excited by near-fault and far-field earthquakes and the distribution regularity of damage under strong earthquakes of group-piles foundation in deep-water bridges were studied. The detailed content of the dissertation are as follows:(l)In order to laid important numerical basis for the folloe-up work, the reasonable water scope and mesh size of fluid domain around the group-piles foundation model established by potential-based fluid method taken fluid-structure coupling interaction into consideration was discussed, and confirmed the values of relevant parameters.(2)To study the dynamic response of the group-pile foundation under different water-depth and the influence of pile spacing on the dynamic response characteristic, seven near-fault earthquake records with obvious velocity pulse effect were chosen as excitation of the group-piles foundation elastic analysis model established by potential-based fluid method. The results show that, with the increase of water depth, the structure vibration period is extending and the existence of hydrodynamic pressure causes the significant increase of dynamic response. In addition, with the increase of pile spacing, the vibration period and dynamic response of structure have a tendency to decrease.(3)Based on the results calculated by potential-based fluid method, the effectiveness of the Morison equation, the simplified formula proposed by Baoxi Wang and Kai Wei respectively used to calculate the hydrodynamic effect was tested, and a specific evaluation of error rate on displacement, bending moment and shearing force calculated by different methods was given.(4)For purpose of study the dynamic response and damage distribution regularity of group-piles foundation under different water-depth, groups of earthquake were chosen to excite the equivalent nonlinear model of group-piles foundation. The study shows that, the dynamic response and the damage of the group-piles foundation of deep-water bridge under near-fault earthquakes are obviously stronger than that caused by the far-field earthquakes. Furthermore, the boundary of the cap and pile is the vulnerabler part of the group-piles foundation, the part buried in the soil of the pile may appear damage at the border of two soil layers in certain depth below the ground and it will spread to both ends of the pile with the enhance of the seismic intensity.