Numerical modeling and modal analysis of base-isolated RC building

Abstract

The purpose of this study is to identify natural frequencies and modes of a base-isolated building by modal analysis using finite element method. In general, multi-degree-of-freedom models are often used to analyze vibration properties of multi-story buildings; however, this modeling is hard to represent spatial behaviors of the buildings such as torsional vibration, and must be considered carefully in case to apply it to base-isolated buildings. In this study, we modelized a base-isolated RC building located in Meiji University as a frame structure combined with floor slabs and aseismic rubbers on the foundation, and computed the natural frequencies and modes of horizontal and torsional vibrations. The primary and secondary natural frequencies of the numerical models agreed approximately with those given by measurements of ambient vibration and seismic waves. The natural modes demonstrated that the aseismic rubbers restrained large deformation of the buildings and worked effectively for seismic isolation. In addition, we observed principal stress distribution of each natural mode. The maximum principal stress of the base-isolated building was relatively small and uniform on each floor, because the columns and floor slabs slid horizontally and did not deform largely. These findings could provide an effective feedback to architects and designers in design phase to consider possible damages on buildings.

Keywords

• seismic isolation
• base-isolated rc building
• seismic wave
• ambient vibration
• natural frequency
• finite element method