POT bearing
POT BEARING:
The basic components of a pot bearing are a shallow cylinder, a pot, an elastomeric pad, a set of sealing rings and a piston. Pot bearings are fixed against all translation unless they are used with a PTFE sliding surface. The pot and piston are made from structural carbon steel, whereas the sealing ring is usually made of a single circular brass ring or a set of two or three flat brass rings. The brass rings are placed in a recess on the top of the elastomeric pad.
Vertical load is carried through the piston of the bearing and is resisted by compressive stress in the elastomeric pad. The pad is deformable but almost incompressible and is often idealized as behaving hydrostatically, however, in practice; the elastomer has some shear stiffness.
Deformation of the pot wall is a concern, since this deformation changes the clearance between the pot and the piston and may lead to binding of the bearing or to elastomer leakage. Rotation about any axis is accommodated by deformation of the elastomeric pad. Pot bearings are usually designed for a maximum compressive strain of 15% in the elastomer due to rotation. To achieve 0.02 radians, the ratio D/t must not exceed 15.
Increasing the pad thickness accommodates larger rotations but increases the required depth, and thus the cost of the pot. During rotation, the elastomeric pad compresses on one side and expands on the other, so the elastomer is in contact with the pot wall and slips against it. This may cause elastomer abrasion and sometimes contributes to elastomer leakage.
The basic components of a pot bearing are a shallow cylinder, a pot, an elastomeric pad, a set of sealing rings and a piston. Pot bearings are fixed against all translation unless they are used with a PTFE sliding surface. The pot and piston are made from structural carbon steel, whereas the sealing ring is usually made of a single circular brass ring or a set of two or three flat brass rings. The brass rings are placed in a recess on the top of the elastomeric pad.
Vertical load is carried through the piston of the bearing and is resisted by compressive stress in the elastomeric pad. The pad is deformable but almost incompressible and is often idealized as behaving hydrostatically, however, in practice; the elastomer has some shear stiffness.
Deformation of the pot wall is a concern, since this deformation changes the clearance between the pot and the piston and may lead to binding of the bearing or to elastomer leakage. Rotation about any axis is accommodated by deformation of the elastomeric pad. Pot bearings are usually designed for a maximum compressive strain of 15% in the elastomer due to rotation. To achieve 0.02 radians, the ratio D/t must not exceed 15.
Increasing the pad thickness accommodates larger rotations but increases the required depth, and thus the cost of the pot. During rotation, the elastomeric pad compresses on one side and expands on the other, so the elastomer is in contact with the pot wall and slips against it. This may cause elastomer abrasion and sometimes contributes to elastomer leakage.
Lateral load is transferred from the piston to the pot by contact between the rim of the
piston and the wall of the pot. The contact stress may be high because the piston rim
may be relatively thin to avoid binding when the piston rotates and the rim slides
against the pot.
The pot wall must transfer the load down into the base plate
(combined shear and bending). The load is then transferred to the substructure
through friction under the base of the bearing and shear in the anchor bolts.
- steel top plates - capable to accommodate longitudinal or transverse sliding movements of the superstructure.
- Stainless steel panels & PTFE - reduce the friction resistance as well as horizontal force.
- Steel piston & internal brass sealing ring - protect the elastomer pad from extrusion.
- Elastomeric pad - behaves like a fluid under high pressure and allows higher working pressure with reduced dimensions.
Types of Pot Bearing
- Free sliding pot bearing is able to slid and rotate in all directions without any restraints.
- Fixed pot bearing restrains movements in all directions. Under loads, the elastomeric bearing pad behaves likes an incompressible confined fluid which enables the rotations on any axis.
- Edge & center guided bearing features fitted edge or center guide to limit the bearing’s movements. It allows for movements in longitudinal or transversal directions.
Applications:
- Incrementally launched bridges.
- Curved or skewed bridges.
- Structures with rotations in various directions.
- Structures using the incremental launching methods.
- Highways and railways, etc
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