A SHAKING TABLE TEST STUDY ON SHEAR TENSILE PROPERTIESOF LEAD RUBBER BEARINGS

摘要

In Japan high rise buildings with seismic isolation devices have increased rapidly in order to obtain bothseismic safety and economical merits. In this paper, one, two and three-dimensional shaking table tests arecarried out to study the hysteresis characteristics of lead rubber bearings (LRB) and especially casessubjected to tensile axial load. A 24-story high-rise building with an aspect ratio of four was the targetedstructure. The super-structure of the testing model, consisting of three stories steel frame, had a totalweight of 250kN and had a length scale of 1/12. Four same LRBs having 100mm-diameter were installedat the distance of 1.08m in the base of the model. In the measurement system, total of 61 sensors wereused. The axial and shear forces acting on every LRB were measured by four three-dimensional loadtransducers. White noise was inputted to identify the fundamental characteristics of the model. The superstructurewas found to have a natural frequency of 3.6Hz and a damping ratio of 2% in both horizontaldirections. El Centro 1940, Taft 1952, Hachinohe 1968 and Kobe 1995(JMA), which were normalized bythe peak velocity values to 25, 50, 75cm/sec, were used as earthquake excitations. Test results aresummarized as follows. I. In total 55 test cases, there were 14 cases where the axial tension in a LRBoccurred. All LRBs suffered over 2MPa tensile stress while the maximum tensile stress was 2.2MPa.After all shaking table tests, static fundamental property tests on the bearings show little change. II. Threedimensionaldynamic response analysis was conducted to simulate the test results. Although axial loads ofthe bearings were observed to vary severely, in a three-dimensional moderate input case, thedisplacements of the base isolation floor and the axial loads in the bearings were simulated well.