Dynamic Response Analysis of Mega-Sub Isolated Structures under Multiaxial Earthquakes

With the use of seismic isolation techniques on mega-sub structures, several scholars have carried out research on them. However, little research has been carried out on mega-sub isolated structures under multiaxial earthquakes. There have been instances in actual engineering where the peak vertical acceleration exceeded the horizontal direction, and the vertical seismic component will also amplify the dynamic response of the structure in the horizontal direction, so in practice, it is necessary to consider the influence of the vertical component of the earthquake on the structure. To investigate the dynamic response of mega-sub isolated structures under unidirectional earthquake and coupled earthquake, this paper used numerical methods to analyze the influences of the horizontal and vertical damping ratio of the isolation layer, the horizontal and vertical frequency ratio of the main substructure, and the mass ratio of the main substructure on the acceleration and displacement of the main and substructure. The optimum parameter values are finally achieved by analytical calculations, which provide a basis for further optimization and practical design of the structure. Finally, the collision between the main and sub-structures in the mega-sub isolated structure was simulated, and the influences of the peak ground motion, main and subframe spacing, vertical seismic component, and sub-structure height on the collision force and acceleration were analyzed. It was shown that the conflict of the main and sub-structures generates instantaneous, large collision forces, which also instantaneously amplify the acceleration and base shear force response, which should be avoided in practical engineering.