Nonlinear Dynamic Response Of Large-size Caisson

With the development of national economy in recent years, the throughput of major ports has gradually increased, corresponding with the high demand of port facilities and structures have become increasingly demanded. More and more large-scale ports appear, the large-scale structure of the pier caisson is widely used in the area which has solid foundation, this kind of large-scale structure's dynamic stability is neglected, but with the occurrence of the Kobe Earthquake ,many caissons damages .In the foundation of"Code of Earthquake Resistant Design for Water Transport Engineering"(JTJ225-98),seismic response analysis of caisson located in Kobe harbor is carried out by using a two-dimensional plane-strain finite element model, including acceleration distribution, anti-slipping and anti-overturning stability. The work and research results are summarized as follows:1. Based on engineering background of the Kobe harbor, the results of caisson are obtained, using calculation methods of current code.2. The static stress analysis of caisson is carried out by using ANSYS software, including the initial deformation and stress before earthquake.3. The seismic responses of Kobe harbor of the rigid base under three seismic waves excitation are analyzed using ANSYS software, including seismic inertial force, hydrodynamic pressure, the stability checking-computation of anti-slipping and anti-overturning, which are compared with those calculated by pseudo-static method .At the same time, the distribution of stress and strain is calculated .In the end, the acceleration distribution curve is compared with the design proposed curve.4. Seismic response analysis of the site is carried out,based on the results of dynamic computation, the seismic waves are gradually enlarge when it spreads from the bedrock to surface .At the same time , the predominant period of the site is founded out and compared with the first period of caisson, then resonance is excluded. In addition, it is indicated that energy concentrates in low frequency, and high-frequency acceleration response is reduced.5. Seismic response analysis of mass-less base is carried out, including the deformation and stress under earthquake, and the dangerous position is found, including acceleration distribution along the caisson wall. Acceleration coefficient increases slowly compared with rigid-base.6. Two-dimensional viscous-spring artificial boundary (VSAB) is modeled through applying COMBIN14 element by using ANSYS software, and the results are compared with those calculated by the method of rigid base and mass-less base and infinity model . The validity of four kinds of artificial boundary is tested. The seismic responses of caisson under VSAB are calculated, and the distribution of stress and strain is also calculated.7. It is indicated that pseudo-static method recommended by the current code for checking stability of caisson is feasible, at the same time, for large-scale pier, numerical simulation can be toke into account as the method of checking stability.