Seismic Response Analysis Of Caisson Foundation Of Trestle In Deep Water Area

The rapid development of economic globalization has led to the increase of China's import and export trade.As the transport hub between land and sea,ports play an important role in the development of national economy.In recent years,in order to meet the country's increasing need for crude oil imports and adapt to the increasingly large-scale transport ships,the terminal is also developing to large-scale and deep-water.Because gravity caisson structures have good stability and the underwater construction technology is relatively simple,the gravity caisson has been widely used in the coastal port construction.In view of the serious damage of Port of Kobe caused by the Hanshin earthquake in Japan in 1995,the seismic behavior of port structures is particularly important.In this paper,the deep-water trestle of a port in the north of China is taken as the engineering background to analyze the seismic response of the caisson which is the substructure of the trestle.The main work and conclusions are as follows:(1)Under the assumption of rigid foundation,Morison equation method and radiation wave method are used to study the interaction mechanism between the caisson and water.The result shows that the existence of water will reduce the natural frequency of the caisson,and the hydrodynamic pressure will increase the dynamic response of the caisson under the seismic excitation.When the depth of the caisson in water is large,the influence of hydrodynamic pressure can't be ignored.When considering the hydrodynamic pressure on the large-scale caisson,the radiation wave theory is more reasonable.(2)Based on the theory of viscous-spring artificial boundary,the layered elastic foundation model considering the radiation damping of infinite foundation is established.According to the wave theory,the mechanism of external wave input is realized,which is suitable for the consideration of transmission and reflection of wave in the layered foundation.It is verified that the wave input mode has good accuracy and applicability by incident complex seismic wave on the layered foundation.(3)In view of the complexity of seabed soil,the whole model of the caisson and seabed layered foundation is established.The seismic dynamic process of the deep-water caisson considering soil-structure interaction is realized.The result shows that the effect of hydrodynamic pressure on shear at the bottom of the caisson is significant after considering soil-structure interaction.Comparing the dynamic response of the deep-water caisson under the conditions of seabed layered foundation,homogeneous foundation and rigid foundation,the time-history curves of displacement at the top of the caisson and internal force at the bottom of the caisson in layered foundation are quite different from that in rigid foundation.The peak value of displacement at the top of the caisson in layered foundation is far greater than that in rigid foundation,while the peak value of internal force at the bottom of the caisson is opposite.Considering the influence of different soil layers on the propagation of seismic wave,the dynamic response of the caisson in layered foundation is larger than that in homogeneous foundation.(4)The Hongnestad's model is used to describe the constitutive relationship of concrete,and the influence of concrete nonlinearity on the seismic dynamic response of the deep-water caisson is analyzed.The result shows that the nonlinear behavior of the caisson is more significant under stronger earthquake,and the concrete near the bottom of the caisson is the first to crack.Concrete material nonlinearity will affect the effect of hydrodynamic pressure on the caisson,one is to enlarge the influence of hydrodynamic pressure on the displacement at the top of the caisson,the other is to reduce the hydrodynamic effect on the internal force at the bottom of the caisson.