Seismic Response Analysis Of Base Isolation Structure Considering Pile-Soil-Structure Dynamic Interaction

In the structural damping control technology,the isolation technology has become one of the most commonly used means of structural damping control because of its simple and understandable concept,stable working performance and low economic cost.The postearthquake survey data of each earthquake in China and abroad fully reflect the superiority of the isolation technology.So far,most buildings around the world have adopted isolation technology as the most effective means to prevent and resist earthquakes.However,a large number of isolation engineering investigations in China and abroad have found that I,II and III sites are more suitable for the construction of isolated buildings.However,in the IV soft soil site,the medium and high frequency components of seismic waves will be filtered out by soft soil,and the spectral characteristics of seismic waves will be changed.When the isolation technology is used to extend the period of the structure,the seismic response will increase rather than decrease.In addition,the theoretical analysis of the isolated structure is based on the assumption that the foundation is rigid,thus ignoring the interaction between the foundation,foundation and structure.In fact,the foundation has an impact on the vibration characteristics of the structure,especially in the soft soil site.It is not comprehensive to only consider the dynamic mechanical properties of the isolation layer and the upper structure.Only fully considering the influence of large deformation of the foundation and soil on the mechanical properties of the isolated structure in the soft soil site,can we design a reasonable isolation structure and ensure its good damping effect and safety.Based on this background,this paper uses ETABS software to simulate different pile-soil coupling systems by different connection elements,and establishes the analysis model of base isolation structure considering pile-soilstructure dynamic interaction.The dynamic time history analysis is carried out to explore the influence of pile-soil-structure dynamic interaction on base isolation structure in IV soft soil site.The main research contents and results are as follows:(1)The basic principle of simplified calculation method of pile-soil-structure dynamic interaction is studied,and the method of using simple spring-damper vibration model to approximate the elastic half-space foundation medium is discussed.The approximate calculation method of foundation stiffness,damping coefficient and additional mass in the vibration model and the impedance of single pile foundation are analyzed.(2)The ETABS software is used to establish the foundation isolation analysis model on rigid foundation and the foundation isolation structure analysis model considering the dynamic interaction of pile-soil-structure.The impedance of the pile-soil structure system is solved by the simplified calculation method,and is equivalently replaced by the spring damper.Then the modal analysis and dynamic time history analysis of the two models are carried out,and the calculation results are compared and analyzed.The results show that the natural vibration period of the base-isolated structure is prolonged and the dynamic response of the base-isolated structure is greatly enlarged after considering the PSSI effect.The PSSI effect reduces the isolation effect of the base-isolated structure,and the amplification of the displacement of the isolation layer will lead to the bearing deformation exceeding the design allowable limit or even damage.(3)The pile-soil coupling system considering nonlinear properties is established by ABAQUS finite element analysis software.The restoring force curve of the pile-soil coupling system is obtained by applying horizontal load at the top of the pile.Then in ETABS software by setting Plastic(Wen)connection element to establish the pile-soil-base isolation structure analysis model,finally the analysis model modal analysis and dynamic time history analysis,the calculation results and the response results of the previous two models were compared and analyzed.The results show that after considering the nonlinear properties,the PSSI effect still plays an amplification effect on the response of the base-isolated structure,but the amplification degree is smaller than that without considering the nonlinear properties.The influence of PSSI effect on the base isolation structure is mainly concentrated in the isolation layer.It is necessary to consider the influence of PSSI effect on the base-isolated structure in design and analysis,and more accurate results will be obtained if the nonlinear properties of materials can be considered.(4)Through the spectrum analysis of the seismic waves directly input into the structure and the seismic waves input into the structure after the foundation soil.The results show that the soft soil will absorb the short period component of the seismic wave frequency component and lead to the long period component.The main frequency band of the seismic wave moves to the low frequency band.At the same time,the soft soil will enlarge the seismic wave power amplitude,which is unfavorable for the base isolation structure.Considering the PSSI effect will change the seismic wave characteristics input to the base isolation structure,if the PSSI effect is not considered,the calculated results will be less than the actual response results,and the designed base isolation structure is unsafe.