Observations

Advanced earthquake mitigation techniques enjoy a greater level of acceptance in Japan than in the United States. 

SOCIAL AWARENESS

The higher level of social awareness is demonstrated by the presence of signs on new building projects which explain the structural system and advanced technologies utilized in the construction as well as the frequency of billboard and televisions adds which describe the structural system used in a particular project.  In addition, the type of system being used is often a selling feature of the building.

Menshinbillboard2 

Subway Billboard

Osaka Subway Station - On the way to visit an isolated building in Osaka, the authors noticed a billboard in a subway station advertising a new "Menshin" (condominium). The billboard specifically mentioned seismic isolation as a major feature of the building.

 

Dai-ichi San-nomiya Building Job Board

Public Display - The job board for one of the buildings visited, described not only the energy dissipation devices used in the project, but showed sketches of the structural system configuration, and numerical information about its (20-30% response reduction).

Amitiesubmittals ENGINEERING

  • There is general preference for hysteretic systems/devices for energy dissipators
  • Target/design drift levels are lower than for comparable U.S. design
  • Three distinct "types" of isolation systems (NRB + external dampers; LRBs ; HDRBs)
  • Lack of an isolation "code" apparently has not retarded the application of the technology. nevertheless there is an extensive review process (BCJ)
  • All designs are based on three standard earthquake motion records (El Centro, Taft, Hachinohe) at  two (sometimes three) intensity/design levels; plus one "site-specific" motion.  Contrary to the U.S. approach of site-specific probabilistic scaling, the Japanese "site-specific" motion is scaled to the predefined intensity/design levels (e.g., for an isolated building in Osaka, a record - obtained where? - from the 1995 Kobe EQ was used)
  • Based on interviews with two of the largest construction companies (Shimizu and Takenaka) it is clear that isolation has moved out of the research arena and into the general design arena. Until just a few years ago, it was usual that a researcher from the company's research group (technical institute) would be closely associated with each project.  This is not the case now as there is only limited involvement as required.
  • Since the vast majority of isolated buildings in Japan are new structures, designers are not faced with the structural/architectural/configurational constraints typically existing with retrofits.  There is a distinct preference for  isolation systems with a minimum number of the largest possible  bearings (this approach results in isolation systems with large displacement capacities)