During the Tohoku earthquake in 2011, high-rise buildings were shaken for quite a long time resulting from the occurrence of long-period ground motions, even though they were located far from the hypocenter. Responses caused by such long-period ground motions can be reduced effectively by adding adequate dampers. This is, however, difficult in the case of high-rise RC buildings because of their high story stiffness and heavy weight. A new vibration control system using shear-walls with a pin at the bottom and oil-dampers is proposed here to achieve it effectively. The bottom of the shear-wall sustains a large axial load and repeated rotary deformation during an earthquake. Then, to establish a durable bottom, a laminated rubber is adopted at the bottom of the shear-wall as a rotary bearing, and is not connected to the base concrete to reduce the tensile deformation of the rubber. The objective of this study is to clarify the behavior of the unconnected laminated rubber in rotary deformation.
First, rotary deformation tests are conducted for evaluating the stiffness, durability, and ultimate state. Since there is no connection, a large bending deformation is produced in the flange because of the uplift of the flange edge, and the tensile deformation of the rubber becomes small. After the tests, there are some changes in horizontal and vertical stiffnesses. The laminated rubber does not break off under the rotary deformation 0.03rad. It can deform in the rotary direction sufficiently regardless of the existence of axial load.
Second, landing and uplift tests are conducted to simulate the actual behavior caused by a varying axial load under earthquake. An inclined plate (angle is 0.01rad) is set on the flange, and the axial load is varied from 0 to 30MPa. Under a low axial load, there is a slit between the sloping plate and the base concrete. But after increasing the axial load (over 5MPa), the slit vanishes completely. The bending moment in the landing and uplift test generally corresponds to that in the rotary deformation tests at 0.01rad.
Finally, in order to conduct rotary deformation tests and to determine the optimal flange thickness, the finite element analysis (FEA) is conducted. Before the uplift of the flange edge, there is no difference regardless of the flange thickness. But after the uplift of the flange edge, the rubber tensile stress decreases with decreasing flange thickness.
It is concluded that the laminated rubber bearing has high durability in the rotary direction, and is suitable as a rotary bearing.
