Design Guidelines for Seismic Isolation in Buildings
About this book
The Architectural Institute of Japan (AIJ) has been at the forefront of seismic isolation research since establishing its Subcommittee for Seismically Isolated Structures in 1986. The resulting Design Recommendations for Seismically Isolated Buildings, now in its fourth edition (2016 English translation), represents the most comprehensive codified guidance available in Japan for the engineering of base-isolated structures. The publication synthesizes decades of theoretical development and real-world evidence, and its scope extends from the fundamental mechanics of isolation devices to sophisticated procedures for verifying structural performance under extreme seismic loading.
At the core of seismic isolation philosophy is the deliberate introduction of a compliant horizontal layer—the isolation interface—between the ground and the superstructure. This layer dramatically lengthens the natural period of the building, shifting it away from the dominant energy content of most earthquake ground motions. The superstructure consequently experiences significantly reduced accelerations and inter-story drifts compared with a conventional fixed-base building of similar proportions.
The AIJ recommendations detail several classes of isolator hardware that achieve this decoupling. Laminated rubber bearings, composed of alternating thin layers of natural or synthetic rubber vulcanized to steel shims, provide the necessary lateral flexibility while sustaining the vertical gravity loads of the building above. The steel laminations prevent bulging of the rubber under compression, enabling these bearings to carry substantial axial loads while remaining highly deformable in shear.
High-damping rubber bearings incorporate special rubber compounds that dissipate seismic energy internally, eliminating the need for separate damping elements in some configurations. Lead-plug isolators—also known as lead-rubber bearings (LRBs)—extend the laminated rubber concept by inserting a central cylindrical lead core into the bearing. The lead core yields under relatively modest shear deformation, absorbing energy through plastic cycling and providing the system with both restoring stiffness and hysteretic damping within a single compact device.
This integration simplifies construction detailing and has contributed to the widespread adoption of LRBs in Japanese practice since the 1980s. The document also addresses friction pendulum systems (FPS), which exploit a concave sliding surface to generate a pendulum-like restoring force whose natural period depends purely on the radius of curvature of the dish and not on the mass of the superstructure. FPS devices are particularly attractive where extremely long isolation periods are desired or where bearing replacement is a maintenance priority.
Beyond device characteristics, the recommendations provide a structured design procedure that begins with the selection of target isolation period and displacement demand, progresses through the determination of bearing layouts and device specifications, and concludes with verification analyses using both equivalent linear methods and nonlinear time-history simulation. Designers must demonstrate adequate performance under two levels of ground shaking: a frequent moderate event associated with serviceability requirements and a rare severe event representing the design basis earthquake. The guidelines include provisions for vertical isolation in buildings particularly sensitive to near-fault vertical ground motion, as well as requirements for inspection, maintenance, and device replacement over the building's service life.
A pivotal section of the 2016 edition reviews the documented behavior of base-isolated buildings during the March 2011 Great East Japan (Tohoku) Earthquake, a magnitude 9.0 event that subjected structures across a vast region to prolonged and intense shaking. Investigations of some seventeen seismically isolated buildings located within the disaster zone found that superstructures sustained virtually no damage even where ground shaking reached Japan Meteorological Agency intensity 6-plus. Occupants in several facilities reported dramatically lower perceived shaking compared with neighboring conventional structures.
Importantly, the extraordinarily long duration of the Tohoku event—significant shaking persisting for two to three minutes—raised new questions about the energy absorption capacity and cumulative fatigue of isolation devices, prompting updates to device qualification testing requirements in the revised edition. The Tohoku data validated and refined key aspects of the earlier design framework while also exposing edge conditions that designers must now explicitly address. The 2016 AIJ recommendations are mandatory reading for structural engineers working on base-isolated buildings in Japan.
Their influence extends internationally, particularly in regions where seismic hazard and building occupancy profiles create conditions where isolation offers compelling life-safety and functional advantages. The document's blend of physical rigor, empirical validation, and practical design procedure makes it an enduring standard reference in the field of earthquake engineering.