# Dynamic Response Analysis of Mega-Sub Isolated Structures under Multiaxial Earthquakes
###### Abstract
[22] proposed the method of partial mass isolation, which can provide multiple vibration suppressors for buildings by isolating different mass parts of different floors, and this method effectively combines traditionally tuned dampers and seismic isolation techniques, resulting in a better aseismic performance of the structure. On the other hand, the action of the earthquake load on the structure can be decomposed into two horizontal components and one vertical component, and there are few studies related to the current mega sub-isolated structure under multiaxial earthquake action. It is not enough to consider only horizontal seismic motion for some buildings with complex and important structures [23], there are multiple instances in practical engineering where the peak vertical acceleration is greater than the horizontal direction [24; 25; 26]. In addition, [PERSON] et al. [27] conducted vertical shaking table tests on an isolated structure. The results indicated that vertical vibration significantly amplifies the vertical acceleration response of the structure. [PERSON] et al. [28] designed a bearing and applied to a steel frame structure to form a seismic isolated structure. It conducted shake table tests on it under coupled horizontal and vertical earthquake excitation. The results showed that the horizontal acceleration response values of the seismically isolated structure under coupled earthquake excitation were significantly amplified. Meanwhile, [PERSON] et al. [29] conducted a shaking table test study on the mega-sub 3D seismic isolated structure and found that the 3D seismic isolation bearing could ensure the vertical isolation and tuned damping effect without making the seismic isolation layer have excessive vertical displace ment. [PERSON] et al. [30] researched Unbonded fiber-reinforced elastomeric isolators (UFREIs), and it was found the isotopically coupled biaxial hysteretic behavior of UFREIs from the test. The vertical earthquake load can influence the mechanical properties of the bearing in the horizontal direction. Considering the actual stress state of the bearing when the earthquake occurs, an efficient nonlinear phenomenological model was proposed to simulate the mechanical behavior of seismic isolation bearings. The design of the structure needs to be considered in many aspects, such as the cumulative influence of earthquake swarm (which refers to the occurrence of consecutive earthquakes in the same area within a short time) [31], which will cause the structure to be subjected to earthquake loads several times within a short time, thus increasing the earthquake response of the structure. Moreover, because a certain relative displacement is generated between the sub-structure and the main structure during the earthquake action when the actual earthquake exceeds the seismic intensity, the relative displacement may exceed the width of the seismic isolation joints and thus lead to the collision between the sub-structure and the main structure. In order to avoid large losses due to collision, it is necessary to research and analyze the collision problem of the main and sub-structure. This article considers the impact of vertical earthquakes, conducts dynamic response analysis on the mega sub-isolated structure, explores the impact of various parameter changes on the seismic reduction effect of the structure, and identifies the optimal parameter values for better design and optimization of the structure.