Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities: Part 8 — Fundamental Properties of Full-Scale Lead Rubber Bearings Based on Breaking Test

Abstract

This paper provides a part of the series “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities.” This part shows the fundamental properties of full-scale lead rubber bearings with 1600 mm diameter based on break tests. The following results are mainly obtained. One: The deformations and the acting loads of the full-scale specimens were accurately obtained up to break by the measurement system for the break tests. Two: The fundamental properties for the full-scale lead rubber bearings with a large-diameter lead plug were obtained by the basic property tests. The load-displacement relations were stable and similar basic properties were obtained among the specimens. Three: The result of shear break tests showed that the hardening property of the specimens had a certain harmony with the hardening stiffness model which was used in the seismic response analysis to investigate the safety margin for severe earthquakes beyond design basis earthquakes of nuclear power facilities. The effect of axial pressure on hardening property was not specifically observed. The evaluated linear strain limit was larger than 250% for every specimen. Four: The softening property of the specimens was obtained from the tensile break tests. The axial stress of tensile yield was approx. 1.4 MPa and the axial stress did not show any negative gradient at least up to approx. 10% axial strain after the tensile yield even with offset shear strains. Five: The tensile force acting on the bolts which secure the specimen to the testing machine was lower than the estimated tensile force at shear break, which indicates tensile force was conservatively calculated to maintain safety in the design for foundation of lead rubber bearings.

International investigation of shear displacement capacity of various elastomeric seismic-protection isolators for buildings

“…Although there are various studies investigating breaking shear properties [5][6][7][8][9], many of these studies use small-scale models of isolators. Furthermore, there is no study investigating and comparing breaking shear properties of various isolators using the same testing system.…”