| With the rapid development of China’s economy, the demand for energy has also increased every year. Because the advantages of widely distributed, high quality, low price and easy exploitation, the LNG(Liquefied Natural Gas) storage tank had become the first choice of energy reserves, and the amount of LNG storage tank construction has also increased. The tanks type has also become larger and larger. However, China’s LNG tank application started late, there is no ability to achieve self-build LNG storage tank, the tank is already in use by the introduction of foreign technology to build, and there are no design specifications, these has greatly limited the development of our economy.Pile foundation is one of the basic form of LNG storage tanks generally accepted, and also an important part of the seismic design of LNG storage tanks. Because pile is the cylindrical member that buried in the soil, damage mechanism of pile foundation is not only related with the earthquake response, it is also related with the vibration of the structure itself, this makes the seismic design of the pile becomes very complex. Due to the unpredictability of earthquakes and the backwardness of the monitoring equipment, resulting in pile earthquake engineering has little experience, which theoretical calculations are still based on the assumption of rigid foundations, ignoring the pile-soil-structure dynamic interaction system, which for the seismic design of LNG storage tank is very unfavorable. For pile- soil- structure dynamic interaction system not only provides an important basis for the design basis for the foundation, but also for the seismic design of the upper structure provides important guidance. Therefore, we considered the pile-soil-structure dynamic interaction system, and used finite difference numerical method to establish the pile-soil-cap system model, and its seismic response under different seismic waves were compared and analyzed, the following main conclusions:(1) Seismic response top of the pile is significantly less than the pile tip. Seismic waves from pile tip to top of the pile communication process, because of the pile and surrounding soil damping exist, it consumed most of the wave energy so that the energy delivered to the upper structure is reduced. Therefore we can increase the length and diameter of the pile appropriately, to reduce the seismic response of the upper structure.(2) The seismic response of pile groups under different post position is not the same. In effect of pile group effect, the farther away from the base center, the greater its earthquake response, earthquake response for the edge of the pile is greater than the canter of the pile. In the design and construction, we should focus on strengthening the bonding strength of the edge of the pile and pile cap.(3) Stress response at the edge of caps is greater than at the center, and it is easily and firstly damaged in the earthquake. So we should pay sufficient attention to the design and construction, such as appropriately increase thickness at the edges or increase its strength of the laying steel.(4) Cushioning layer can play a very good shock absorption effect for the cap. Compared to non-damping cap, the caps damping amplitude decreases more than 70% on average in seismic loads.(5) In different seismic waves, the displacement of top of the pile reaction increases with an increase in acceleration of seismic wave, and in the same time interval of acceleration, waveform of El-Centro wave and artificial waves can produce greater seismic response than Tianjin wave. |
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