Yasuo Takenaka

Seismic Performance of Seismic-isolated Building for Long-period Ground Motion and Limited Performance of Seismic Isolator

earthquakes. The Special Investigation Committee on Response to Catastrophic Disasters Including the Anticipated Tokai Earthquake (chair: Hiroshi Akiyama) of the Architectural Institute of Japan (AIJ) has been carrying out research to prepare for the occurrence of these earthquakes. The committees report clarified the need to study the cumulative energy absorbing capacity and other performance parameters of seismic isolators, as well as the maximum value of seismic isolation layer displacement and other responses by seismic-isolated buildings under long-period earthquake motions. Further, the report demanded further verification of the critical performance of these buildings under larger earthquake motions than assumed in the design phase. 1),2) By Revision of the Building Standard Law in 2000, use of isolators and dampers approved by the Minister has been stipulated in the design procedure of isolation buildings. As verifications of various characteristics by testing full-scale specimens are required to obtain the approval, the manufacturers carried out a lot of experiments, which have made characteristics of various isolation devices clearer 3),4),5),6) .

SHAKING TABLE TESTS ON THE ULTIMATE BEHAVIOR OF SLENDER BASE-ISOLATED BUILDINGS SUPPORTED BY LAMINATED RUBBER BEARINGS

This paper describes the results of shaking table tests on a slender base-isolated building model supported by four laminated rubber bearings to clarify the ultimate behavior when bearing fracture occurs. The results of the tests indicate that the ultimate behavior of the base-isolated building is roughly classified into two types; one is caused by buckling fracture of the bearing, and the other is a result of tensile fracture of the bearing. In the buckling type, one of the standards for judging the occurrence of buckling fracture is that the lateral deformation exceeds the value corresponding to the diameter of the bearing, and the aspect ratio of the building does not have much effect on the ultimate behavior. In the tensile type, tensile deformation becomes higher with an increase in aspect ratio, and the ultimate input level does not decrease. The building has a safety margin to fracture even if the aspect ratio becomes larger.