Seismically isolated (SI) buildings are thought to be fragile when subjected to excessive input ground motions beyond design level.The authors have been proposing a new isolation bearing which has much higher seismic safety than conventional bearings.Supporting a superstructure only by the proposed bearings will enable the whole SI building to protect from any structural damage.In this paper, the development process of the proposed bearing, including the selection of the most suitable slider material, dynamic loading test of a scaled bearing, and quasi-static loading test of a full-scale bearing, is mentioned. Preliminary and detailed time history analyses of SI building models are also shown. The research results lead to the conclusion that a system applying the proposed bearings realizes an SI building with higher seismic safety than ever, if only provided a large enough isolation gap.

Dynamic and quasi-static loading tests for scaled and full-scale FSLRB, a new isolation bearing which consists of a conventional lead rubber bearing (LRB) and a slider bearing in series, are mentioned. The test results show that torsional behavior of LRB part in bi-directional excitation does not affect the limit state of the bearing, and both dynamic and static friction coefficients are accurately estimated by newly proposed equations utilizing effective surface pressure instead of mean surface pressure. As a conclusion, the authors think that the bearing is ready for the practical use in an isolation system with even higher seismic safety.

We researched aging of the LRB (Lead Rubber Bearing) installed in a base-isolated building which was constructed 15 years ago. The hardness of the cover rubber and the height were measured for 35 LRBs which were installed in the building. The compression test and combined compression shear test with monitor samples and actually installed LRB were performed to search changes in their hysteresis characteristics. The monitor samples were composed of 4 LRBs and 1 RB. Main results obtained were as follows: 1) The LRBs installed in the TC building crept approximately 1 (mm) during 15 years and did not changed during last 5 years. 2) The hardness of the cover rubber did not change against that of 15 years ago. 3) From the testing of the monitor samples, the compression stiffness increased approximately 17% and the shear stiffness increased approximately 5%, however the yield force changed quite a little during 15 years on average. As a result, the suitability of the design specifications of the LRB was confirmed.

No abstract