Types of Bridge Bearing

Types of bridge bearing 

1. Elastomeric Bearing

a.Plain elastomer pads

b.Laminated Elastomeric bearings

2.Sliding bearing Mechanism

a. PTFE  sliding material

b.Alternative sliding material

3.High load multi Rotational building:

a.Pot bearing

b.Disc bearing

c.Spherical bearings

4. Fabricated steel mechanical bearing

a.Rocker bearing

b.Rocker cum rolling bearing

Elastomeric Bearing:

It consists of elastomer manufactured from synthetic or natural rubber and can take both translation and rotation movements through elastomer deformation. The ability of elastomer to carry large vertical loads is because of reinforcement provision that prevents lateral bulging of elastomer.

There are number of elastomeric bearing pads classified based on types of reinforcements used. For example, steel reinforced, plain, fiberglass reinforced and cotton duck reinforced elastomeric bearing pads

Strength and response of each type is different, steel reinforced elastomeric bearing is the strongest one and plain elastomeric pad is the weakest.

a.Plain Elastomeric Bearing

Plain elastomeric bearing with the simplest structure among all bearing products is exclusively manufactured from natural rubber or neoprene rubber. It is considered to be a low cost choice for short span bridges, prefabricated structures, buildings as well as flyovers, etc.

b.Laminated Elastomeric Bearing

It is manufactured through the process of vulcanization and moulding to form a homogeneous unit with layers of steel plated embedded in. Comparing with plain elastomeric bearing, this one has higher vertical load capacity, excellent vibration and sound isolation. It is ideal for bridges with short span and flyovers,  etc. 

2.Sliding Bearing Mechanism

Sliding bearing consist of two metal plates, commonly stainless-steel plates, that slide relative to each other and hence makes room for translational movement and lubricating material between them.

Sliding Bridge Bearing

A friction force is generated in sliding bearing and it is imposed on substructure, superstructure and sliding bearing itself. So, it may be required to provide lubricant such as polytetrafluoroethylene (PTFE) to decline generated friction.

It is specified by ASSHTO that sliding bearing cannot be used unless the bridge span is smaller than 15m. This is because sliding bearing cannot be purely used if the bridge experiences rotation movement.

However, the span restriction for sliding bearing utilization can be disregarded when it is used in combination with other bearing types.

PTFE Sliding Material.

PTFE top elastomeric bearing, a variation of traditional laminated elastomeric bearing , features a layer of PTFE bonded to top surface of the bearing. In conjunction with lubricant in the dimples of PTFE, the bearing allows for excellent sliding movements with reduced friction coefficient.

High load Multi Rotational building

Pot Bearing

Pot Bearing is the widest used type designed for structures using the incremental launching methods, highways and railways, etc. PTFE top elastomeric bearing is fitted in the steel pot plate to ease the sliding movements with the help of a stainless steel panel welded on top steel plate.

Disk Bearings for Bridges

Rotation movement is accommodated through the deformation of elastomer whereas the translation movement is considered through the application of PTFE slider.

The utilized elastomer should be adequately hard to support vertical loads without suffering large deformations and sufficiently flexible to allow rotational movement.

Both vertical loads and lateral loads are supported by elastomeric disk and metal ring in the center of the bearing respectively.

 Spherical Bridge bearing

Spherical bridge bearing features its precision-machined steel plates with concave ad convex surfaces. And it can accommodate large movements and rotations in excess of +/- 0.03 radians. Spherical bridge bearings can be applied to structures with large turning angles, wide and curved bridges regardless of low temperatures even under -30℃.

Lead rubber bearing, as its name implies, has a lead plug in the middle of the bearing that will assist the bearing to absorb earthquake-generated forces, extending the structure vibration period. In this way, lead rubber bearings protect buildings or structures from damages and severe deformations caused by earthquake.

Curved Bearings for Bridges

 If curved bearing is cylindrical, then it only accommodates rotation movements. However, both rotation and translational movements can be dealt with if curved bearing is spherical.

Due to the fact that both gravity loads and curved geometry generate lateral resistance against and consequently lateral movement would be limited, that is why  polytetrafluoroethylene (PTFE) slider is adhered to the bearings in order to make rooms for lateral movements. 

Fabricated steel mechanical bearing

a.Rocker Bearing

Rocker is an expansion bearing composed of curved surface at the bottom, which accommodate translational movement and a pin at the top makes room for rotation movement..

PIN bearing:

Pin bearing is a fixed bearing that make room for rotation movement through the application of steel pin. It has similar structure and component like rocker bearing apart from the bottom of pin bearing which is flat and fixed to the concrete pier.

Roller Bearings for Bridges

Roller bearing can be used in the construction of reinforced concrete and steel bridge structure. There are two main configurations including single roller bearing which is composed of one roller placed between two plates and multiple roller bearing that consist of several rollers installed between two plates.

Multi roll bearing make room for translation movement only and rotation movement can be accommodated if rollers are combined with pin bearing. Multiple roller bearings are expensive and support considerably large vertical loads.

b.Rocker cum rolling bearing

These type of bearings consists of rollers sandwiched between a saddle plate and a bottom plate. Rocker cum roller bearings offer longitudinal movement through rollers which roll along guide bars attached to saddle plate and bottom plate. Rotational movement is through a rocker pin which gives a see-saw rocking motion to the top plate. The rollers are connected by a spacer plate for unidirectional movement.