Structural Bearings are devices installed in bridges, buildings and other structures to transfer loads and to restrain or release certain degrees of freedom of both displacement and rotation.
Depending on design requirements, FIP bearings can be divided into the following main categories:
POT Bearings: Steel bearings in which the rotations about any horizontal axis are ensured by the deformability of the elastomeric pad confined in a monolithic steel pot.
SPHERICAL Bearings: Steel spherical hinges in which the rotations about any horizontal axis are allowed by the sliding of a convex steel element in a concave element.
ELASTOMERIC Bearings: Reinforced rubber bearings consisting of a rubber pad, hot vulcanized together with one or more steel laminates.
Apart from the traditional types of bearings defined above, FIP MEC can tailor design and manufacture special bearings such as with uplift capacity, temporary restraining, with damping capacity, disk bearings, etc. depending on design requirements.
Typologies
Vasoflon® are structural pot bearings, in which the rotations about any horizontal axis are allowed by the deformability of the elastomeric pad confined in a steel pot.
The elastomer behaves like a fluid that, under a tri-axial pressure, offers low resistance to deformations but high vertical stiffness.
In addition to vertical compressive loads, Vasoflon® bearings are capable of transferring forces and/or sliding in one or more horizontal directions, depending on the different bearing types: fixed, free sliding, guided sliding.
In the sliding bearings, movements are achieved through the mutual sliding of two flat mating surfaces, one of polished stainless steel and the other of PTFE.
Classification
Vasoflon® bearings are classified using two digits with the following meanings:
- VF Vasoflon® bearing, fixed type
- VU Vasoflon® bearing, guided type, longitudinally
- VU* Vasoflon® bearing, guided type, transverse sliding
- VM Vasoflon® bearing, free sliding type
Key Features
- Very frequent use in road bridges
- Maximum rotation 2%. Recommended rotation ≤ 1%.
- Suitable for a temperature range from -35°C to +48°C (EN 1337)
- Available in accordance with EN 1337-5, CE marked and AASHTO design codes, but not only
- They can be CE marked, meet EN 1337-7, AASHTO or other design codes
Sferopol® structural bearings are spherical hinges in which the rotations about any horizontal axis are allowed by the sliding of a convex steel element, covered by a layer of polished stainless steel, in a concave element coated with low sliding material.
In addition to compressive loads, Sferopol® bearings are capable of transferring forces and/or sliding in one or more horizontal directions, depending on the different bearing types: fixed, free sliding, guided sliding.
Sliding element for horizontal movements is flat.
Sliding movements, both rotational and flat, are achieved through the mutual sliding of two flat mating surfaces, one of polished stainless steel and the other of low friction material. As low friction material both PTFE or SMF (Sliding Material FIP) can be used. SMF, made of UHMWPE (Ultra High Molecular Weight Polyethylene) is highly resistant to wear and tear, and significantly extends the life of the bearings and therefore of the structure.
Marking
Sferopol® bearings are classified using two digits with the following meanings:
- SF Sferopol® bearing, fixed type
- SU Sferopol® bearing, guided type, longitudinally
- SU* Sferopol® bearing, guided type, transverse sliding
- SM Sferopol® bearing, free sliding type
Key Features
- Very frequent use in road bridges
- Suitable for high rotations, more than 2%
- Temperature range between -50°C to +70°C
- They can be CE marked, meet EN 1337-7 (PTFE), ETA 09/0226 (SMF), AASHTO or other design codes.
Type ELASTOFIP®
Elastofip® are structural bearings made of reinforced elastomer, consisting of an elastomeric pad, in which steel laminates are hot vulcanized to the rubber, there key feature is on top and bottom mechanical anchoring to the structure, which makes them suitable also for seismic areas.
Marking
The most common type is EF (Elastofip® fixed). It permits deformations in all horizontal directions and the same time produce elastic reactions proportional to the deformations.
Guided sliding EU/EU* and free sliding EM can also be supplied.
Key Features
- Maximum rotation 1%.
- Available with different type of rubber compounds (NR/CR) and sizes.
- They can be CE marked, meet EN 1337-3, AASHTO or other design codes.
Type NEOARM®
Neoarm® are structural bearings made of reinforced elastomer, consisting of an elastomeric pad, in which steel laminates are hot vulcanized to the rubber. Reinforced rubber bearings consisting of a rubber pad, hot vulcanized together with one or more steel laminates. Corrosion protection provided by vulcanisation into rubber.
Key Features
- Maximum rotation 1%.
- Available with different type of rubber compounds (NR/CR) and sizes.
- They can be CE marked, meet EN 1337-3, AASHTO or other design codes.
Disk Bearings (POLIDISK®, PF, PU/PU*, PM, etc.)
In Disk Bearings, a disc of Polyether-Urethane (PU) material placed between two steel plates, acts as rotation hinge. The PU elasticity enables rotational movements of the upper plate around any horizontal axis. A pin placed in the centre of the rotational element withstands horizontal forces and keeps the upper and lower plates in position. Bearings can be fixed, guided sliding or free sliding.
Anti-uplift bearings
Uplift bearings are normal fixed, guided or free sliding bearings, but are provided with additional external clamps and/or internal pin that enable the bearings to resist traction loads, they do not open-up in case of uplift. The bearings can withstand traction forces both at SLS and ULS.
Load measuring bearings
They permit in situ measuring of vertical load acting on the bearing. Depending on the technology used, measurements can be read on the bearing itself or at a remote location at any time during the service life of the bearing.
Bearings with dampers
These are a combination of one sliding bearing with hysteretic and/or viscous dampers. They are also called "flat sliding isolators with dampers".
Bearings with shock transmitters
Sliding bearings coupled with shock transmitters. In case of sudden movements, for example seismic movements, the shock transmitters prevent the relative movements of the structural elements connected to them, thus temporarily transform the bearings from sliding into fixed in the needed direction.
Elastic reaction bearings
Fixed or guided sliding Vasoflon® o Sferopol® bearings, in which horizontal stiffness is reduced by elastomer elements.
Bearings for incrementally launched bridges
Bearings designed in such a way as to allow for the sliding of the bridge deck during launching operation, by means of a supplementary special stainless steel fixed to suitably machined upper side of the bearing, which can be removed after completion of launching.
Bearings with temporary restraints
Sliding bearings with additional temporary restraints that allow them to be fixed during a first phase, for example casting of a bridge deck or launching of a bridge, and subsequently become sliding by removing the temporary restraints.
Temporarily sliding bearings
Bearings that are initially free sliding, for example so as not to oppose displacements generated by the construction phase, and subsequently become fixed or guided sliding by adding supplementary restraints or guides.
