| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 104 === Rubber bearings used in base isolation consist of laminated elastomeric layers bonded between rigid plates. To reduce the weight of bearings and allow for the penetration of heat during vulcanization, some of the large circular bearings have a central hole, which leads to annular rubber bearings are often employed in seismic isolation. This study investigates the tilting stiffness of annular elastic layer.
An annular elastic layer bonded between rigid plates and subjected to pure bending moment is analyzed through a theoretical approach base on two kinematic assumptions: (i) planes parallel to the rigid bonding plates before deformation remain planar after loading; (ii) lines normal to the rigid bonding plates before deformation become parabolic after loading. The horizontal displacements are solved by satisfying the stress boundary conditions of the bonded layers. The tilting stiffness of bonded annular bearings is then derived. Throughout theoretical approach, the displacement solutions in the radial and tangential directions are shown to be proportional to cosθ and sinθ, repectively, and do not contain any higher term of trigonometric funcitons. The effective bending mudulus increases with increasing shape factor or increasing Poisson’s ratio. While the Poisson’s ratio is close to 0.5, the larger the shape factor is, the larger increment of effective bending mudulus has. When the ratio of outer radius to thickness is fixed, the effective bending mudulus decreases, for larger annular hole. The stiffness reduction caused by the central hole is more proment when the Poisson’s ratio is closer to 0.5.
Finite element analysis is also came out in this study. The tilting stiffness under different parameters are analyzed by using two different element types, which are the linear hexahedral isoparametric element(H8) and the modified incompatible hexahedral element(HM11). The HM11 element have a better performance than H8 element. The effective bending mudulus of theoretical solution is very close to finite element solution for smaller annular hole, but has larger deviation for larger annular hole, because the second kinematic assumption in theoretiacal approach maybe not suitable for larger annular hole.
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