A Proposal of an Isolation System With Higher Seismic Safety Against Input Ground Motions Beyond Expectations

Abstract

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.

Practical application of lead rubber bearings with fail‐safe mechanism

“…Considering the aforementioned facts, the authors conducted a variety of tests, including bi‐directional dynamic loading tests of actual‐size FSLRB specimens. This report presents additional experimental results to that of previously reported research and technical publications…”

“…Table shows the dimensions and properties of the 4 types of FSLRB test specimens mentioned in this report, together with the 3 specimens tested in Reference . Basically, 4 square‐shaped sliders are set in parallel and are adhered to the slider holder because the maximum available size of the slider material is approximately 500 × 500 mm due to manufacturing limitation.…”

“…In the tests conducted in Reference, uplift of the outer edge of the slider was observed under compressive loading in the specimens with relatively low out‐of‐plane stiffness in a group of steel plates positioned between the LRB and the slider bearing components (connecting plate, bearing plate, and slider holder. See Figure ).…”

“…The collision of superstructures with moat walls, excessive seismic response of superstructures and damage to isolation devices are expected as major limit events in general SI buildings subjected to earthquakes exceeding the design level. Figure shows a classification of these limit events and available countermeasures . The shaded 3 terms in the bottom of Figure indicate the representative technologies.…”

“…The authors conducted uni‐directional dynamic loading tests for scaled FSLRB specimens with dimensions of 414 × 414 mm LRB (Sq.‐414 Specimen) and uni‐directional quasi‐static loading tests for actual‐size FSLRB with dimensions of 900 × 900 mm LRB (Sq.‐900A Specimen), to evaluate the basic properties and behavior of the bearing . However, the following matter was unresolved with respect to the application of the bearing to actual buildings.…”