Proposed Reformulation of Static Lateral Response Procedure for Simplified Base Isolated Design

摘要

SEAONC's Protective Systems Committee (PSC) believes that simplification of the design and analysis process for isolated structures will encourage more widespread use of the technology. The behavior of a base isolated structure resembles a single degree of freedom system more than most conventional structures, however current base isolated codes often require sophisticated analytical methods such as a nonlinear response history. Even non-essential low-rise buildings without structural irregularities frequently require a response spectrum analysis. By reformulating the code static method equations for minimum lateral displacements and force levels, PSC has developed a method to enhance the usability of the present static analysis procedures. PSC has chosen to focus on varying the tangible properties of isolation systems; yield strength and post-yield stiffness. By accounting for upper and lower bound properties, limiting hysteretic damping, and preserving code restoring force requirements, trends emerged in the resulting isolation design parameters. These trends allow for a single table and chart to be used to determine design base shear and maximum displacement. Using this procedure an engineer can complete the static analysis of the building using design procedures that closely resemble those used for fixed base structures, eliminating the need for complex modeling of the isolation system. The parameters used in the procedure relate directly to the design of isolator units and thus facilitate rapid development of isolator product specifications and cost estimates.