A distributed flexibility and damping strategy to control vertical accelerations in base-isolated buildings

Seismic isolation is an effective method for protecting the structural system, nonstructural systems and content from the damaging effects of strong horizontal earthquake ground shaking. However, seismic isolation devices widely used in the USA and elsewhere are not designed to protect nonstructural components and content from strong vertical earthquake ground shaking. Past research efforts aimed at developing three-dimensional isolation have resulted in systems that have limited application or are overly complex, cost prohibitive and unproven. A distributed flexibility and damping concept to control vertical acceleration demands in base-isolated buildings is explored in this study. Unlike past efforts to achieve three-dimensional isolation that concentrate both the horizontal and vertical flexibility at the base of the superstructure, the vertically distributed flexibility and damping concept explored here consists of one or more planes of laterally restrained column bearings distributed at discrete locations up the height of a base-isolated superstructure. The laterally restrained column bearings increase the vertical flexibility and damping in the superstructure without increasing rocking displacements. An analytical study was performed to understand the influence of incorporating vertical flexibility and damping in a base-isolated frame and to evaluate the effectiveness of the concept for controlling vertical acceleration demands. The distributed flexibility and damping concept is shown to significantly reduce vertical acceleration demands and the likelihood of damage to suspended ceiling systems by comparison with an identical conventionally base-isolated frame. Copyright (c) 2013 John Wiley & Sons, Ltd.