Attenuation Zones Characteristics Of Combined Layered Periodic Foundation

Periodic structures possess a unique dynamic property of frequency attenuation zones in which the vibration of frequencies in attenuation zones will be attenuated.Based on characteristic of attenuation zones,scholars propose to use layered periodic foundation for base isolation in the field of civil engineering.There are two main limitations exist in the resent researches on the layered periodic foundation: firstly,the local sensitivity analysis method of "changing individual parameter at a time" is mainly used to study the effect of material and geometric parameters on attenuation zones of traditional layered periodic foundation.However,the above analysis method fails to identify the most influential parameter affecting the attenuation zones and cannot be able to quantify the interactions of different parameters.Therefore,some scholars proposed the global sensitivity analysis method to study the influence of material parameters and geometric parameters on the attenuation zones of traditional layered periodic foundation.However,research on the global sensitivity of attenuation zones in traditional layered periodic foundation has just started,and only a few studies also have the disadvantages of poor convergence and large amount of calculation.Secondly,the main frequency components of seismic waves span the range of 1 Hz～20 Hz.However,it is difficult to design attenuation zones with both“low starting frequencies” and “large bandwidths” for traditional layered periodic foundations with identical unit cells to cover the above frequency range.Therefore,this will restrict the potential application of layered periodic foundation,a new isolation technology.In order to solve the above problems,in this paper,a global sensitivity analysis method based on the Gauss-Lobatto integration is proposed and applied to study the attenuation zones of traditional layered periodic foundations.The generation mechanism of attenuation zones of combined layered periodic foundation which can obtain "low and wide attenuation zones" is studied.The theoretical results of combined layered periodic foundation and its isolation performance are verified by numerical simulation The main research contents and results are as follows:1.Sobol’ sensitivity analysis based on Gauss-Lobatto integration is proposed,and the correctness of the method is verified by an example.Global sensitivity analyses of lower bound frequency,width and maximum attenuation coefficient of the first attenuation zone are conducted.Based on the analysis results,the fitting equations of the lower bound frequency,width and maximum attenuation coefficient of the first attenuation zone are proposed,and the correctness of the fitting equations is verified.The results show that for the lower bound frequency of the first attenuation zone,the periodic constant,initial stress ratio,mass density ratio of the two materials in the traditional layered periodic foundation and filling ratio of rubber are important parameters separately.For the width of the first attenuation zone,the filling ratio of rubber,periodic constant and their interaction are the three most important parameters.For the maximum attenuation coefficient of the first attenuation zone,the filling ratio of rubber is the dominant parameter.2.The frequency response function is used to identify the combined attenuation zones of combined layered periodic foundation.By analyzing the effect of the number of unit cells,arrangement and composition on the combined attenuation zones of combined layered periodic foundation,the mechanism of combined attenuation zones of combined layered periodic foundation is revealed.The results show that the generation of the combined attenuation zones of combined layered periodic foundations results from the contribution of the attenuation zones of both the traditional layered periodic foundations.Therefore,the combined attenuation zone of combined layered periodic foundation can be regarded as the union of the attenuation zones of traditional layered periodic foundations in the combined periodic foundation.3.The finite element model of combined layered periodic foundationsuperstructure and its same size concrete foundation-superstructure is established,and the harmonic response and seismic response of the models are analyzed by ANSYS finite element analysis software.The results show that the combined attenuation zones of combined layered periodic foundation are of both comparatively low starting frequency and large bandwidth,and the acceleration response in the combined attenuation zones and the maximum interlayer relative displacements of the superstructure can be effectively attenuated.The correctness of this theory is further verified.