TIS Pot Bearing (TPB), produced by TIS Technological Isolator Systems Inc., is a structural bearing which is used for connecting different structural elements (substructure and superstructure) and controlling force and displacement demands developed between the structural elements. The working mechanism of TPB is to transfer the forces developed on the superstructure to the substructure with desired rate, and to allow the rotations on the substructure and the other movements developed by the actions listed below.
- Shrinkage and expansion in concrete
- Seismic effects
- Temperature changes
TPB devices are designed according to the requirements applicable to relevant parts of EN 1337, mainly EN 1337-2 and EN 1337-5.
TPB devices are produced in three different types according to the force and displacement interactions that need to be accommodated. TPB’s that TIS Inc. produce are listed below.
- Fixed pot bearing: TPB-FX
- Free sliding pot bearing: TPB-FS
- Guided sliding pot bearing: TPB-GS
TPB-FX consists of an elastomeric pad placed inside a steel pot, and a steel piston pressing and rotating on the elastomeric pad. This type of bearings resists horizontal displacement demands in any direction and only allows superstructure to rotate about any horizontal axis. Elastomeric pad, placed inside the pot, resists the compressive pressure that the vertical load produces by behaving like an incompressible fluid in a confined volume, and allows the rotation of the piston with shear deformation in the elastomer. The contact between the piston and the pot wall transfers the horizontal forces on the superstructure and the piston connected to it, to the substructure.
TPB-FS is composed of a TPB-FX type device and an upper plate that is free to slide on top of the piston in any horizontal direction. This sliding surface is composed of a dimpled PTFE sheet fixed in a recess on the piston and a polished stainless steel fixed on the lower surface of the upper plate. This sliding surface allows the superstructure to move freely in any horizontal direction relative to the substructure, with the low friction provided by the lubricant in the dimples of PTFE sheet. Besides, the horizontal forces on the superstructure are not transferred to the substructure.
TPB-GS is almost the same as TPB-FS but this type of bearing has a guide in the middle of the top of the PTFE-placed piston, in the direction of the design movement. Besides there is a canal in the middle of the upper sliding plate that the guide is placed and slide inside. The guide allows the superstructure to move only in the direction of the design displacement and prevents it to move in all other horizontal directions and while doing that, transfers the horizontal forces developed in those directions to the subassemblage and to the substructure with the contact between the guide and sliding plate.
2- Elastomeric pad and internal seal
6- CM1 Composite material
7- Upper sliding plate
8- Polished stainless steel
9- Anchorage bolts
10- Dust protection
Pot, piston, guide and upper sliding plates of the TPB devices are produced from S355 structural steel. It is advantageous to use S355 structural steel for both design and production of the devices since it is a well-known material. This material has also proven its performance under various structural loads.
Elastomeric pad, which has a 60 MPa compressive strength and a hardness of at least Shore A 50, transfers the vertical loads to the substructure without damaging the bearing, and provides strength against the rotational movements without being damaged during the operating time of the device.
High quality POM or carbon-filled PTFE seal is used in order to prevent the elastomeric pad from bursting out of the pot and prevent any pad damage during the rotational movements.
Dimpled PTFE sheets, having a compressive strength of 90 MPa, is used in TPB-GS and TPB-FS devices and lubricants are used to provide high compressive strength against vertical loads and low friction for sliding movements.
Composite material with a compressive strength of 200 MPa and a low friction coefficient is used on the sides of guides in TPB-GS in order to resist high horizontal loads transferred from upper sliding plate to the guide.