3D-BASIS - Nonlinear Dynamic Analysis of Three-Dimensional Base Isolated Structures: Part II

Keywords: Base Isolated Structures, Three Dimensional Structures, Base Isolation Devices, Pseudo Load Formulation, Nonlinear Dynamic Analysis, Computer Programs, Dynamic Analysis, Nonlinear Behavior, Mathematical Models, Hysteretic Models, Analytical Models, Multistory Buildings, 3D-BASIS, Secondary Systems, and Protective Systems.

Abstract: Structures can be designed to withstand severe earthquake forces by providing ductility and energy dissipation capacity to the structural elements, thus allowing damage in the structural elements and invariably in the nonstructural elements. Another approach which is being rapidly adopted all-around the world is the concept of base isolation, wherein the flexibility and the energy dissipation capacity are provided by a specially designed isolation system that is placed between the superstructure and the foundation. These isolation systems can be designed to essentially limit the nonlinear behavior to the isolation level, imposing little or no ductility demand on the superstructure. The study of three-dimensional behavior of base isolated structures requires a comprehensive analytical model. The analytical model should be capable of addressing highly nonlinear behavior of isolation systems such as sliding systems and elastomeric bearing systems (with biaxial effects). The existing analytical models and solution algorithms cannot accurately analyze sliding systems or combined elastomeric-sliding systems. This report deals with the development of a comprehensive analytical model and solution algorithm for nonlinear dynamic analysis of three-dimensional base isolated structures and the development of a computer program 3D-BASIS. A new analytical model and solution algorithm involving the pseudo-force method is developed. New biaxial and uniaxial models of isolation elements are developed. The novelty of the analytical model and solution algorithm is its capability to capture the highly nonlinear frictional behavior of sliding isolation systems in plane motion. Nonlinear behavior is restricted to the base and the super-structure is considered to be elastic at all times. The nonlinear isolation system may consist of elastomeric and/or sliding bearings, linear springs and viscous elements. The solution algorithm consists of the pseudo-force method with iteration. Comparison of the computed results with experimental results is presented for verification. A six-story reinforced concrete base isolated structure is analyzed to demonstrate the efficiency of the algorithm.