structural engineering Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and joints' that create the form and shape of human-made Structure#Load-bearing, structures. Structural engineers also ...

, a bridge bearing is a component of a

bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

which typically provides a resting surface between

bridge pier The pier of a bridge is an intermediate support that holds the deck of the structure. It is a massive and permanent support, as opposed to the shoring, which is lighter and provides temporary support. History Until the advent of concrete and ...

s and the

bridge deck A deck is the surface of a bridge. A structural element of its superstructure A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildin ...

. The purpose of a bearing is to allow controlled movement and thereby reduce the stresses involved. Possible causes of movement are

thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...

and contraction, creep, shrinkage, or

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

due to the properties of the material used for the bearing. External sources of movement include the settlement of the ground below, thermal expansion, and

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

. There are several different types of bridge bearings which are used depending on a number of different factors including the bridge span, loading conditions, and performance specifications. The oldest form of bridge bearing is simply two plates resting on top of each other. A common form of modern bridge bearing is the elastomeric bridge bearing. Another type of bridge bearing is the mechanical bridge bearing. There are several types of mechanical bridge bearing, such as the pinned bearing, which in turn includes specific types such as the rocker bearing, and the

roller bearing In mechanical engineering, a rolling-element bearing, also known as a rolling bearing,ISO 15 is a bearing which carries a load by placing rolling elements (such as balls, cylinders, or cones) between two concentric, grooved rings called race ...

. Another type of mechanical bearing is the fixed bearing, which allows rotation, but not other forms of movement.

History

The first bridge bearings to be used were plane bearings in the early 1800s, which included sliding bearings or roller bearings. Plane bearings allowed horizontal movement in one direction, and could therefore transfer horizontal load. Rotating bearings were used in the late 1800s and early 1900s and included rocker bearings, knuckle bearings, and ball bearings. Rotating bearings allowed movement in both the horizontal and vertical directions. Both plane bearings and roller bearings were made of metal. In the mid-1900s, deformation bearings began to be used, which were made of rubber. Deformation bearings primarily include elastomeric bearings, the most common type of bridge bearing used today.

Types of bridge bearings

Rocker bearings

Rocker bearings have curved surfaces that allow rocking. As the bridge expands, the bearing rocks to allow movement in the horizontal direction. Rocker bearings are primarily made of steel. Rocker bearings tend to be used for highway bridges.

Elastomeric bearings

Elastomeric bridge bearings are the most popular type of bridge bearing used today. They are made of rubber and do not have any moving parts, because the rubber itself allows movement in the bridge. Elastomeric bearings can be made at a low cost, and do not need to be maintained, like other forms of bearings that have moving parts and are made of metal. Elastomeric bearings can be reinforced with steel to make them stronger if needed.

Sliding bearings

Sliding bearings have both a flat sliding surface to allow horizontal movement and a spherical surface to allow rotation. Although they used to be made of metal, sliding bearings now tend to be made of

Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, and has numerous applications because it is chemically inert. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a spin-off from ...

Spherical bearings

As the name suggests, spherical bearings are in the shape of a sphere. These bearings only allow rotation, and prevent movement in the horizontal and vertical directions.

Functions of bridge bearings

They are one of the most important components of bridges. * They transfer forces from bridge superstructure to substructure. Mainly two types of loads: Vertical Loads such as the structure's weight and vehicle load, and Lateral Loads including earthquake and wind forces. * They permit movements like translation and rotation in between girders and pier caps of bridges to accommodate movements such as thermal expansion. * Neoprene bearing pads (rubber like structure), a special type of bridge bearing, loses its energy through deformation. * It simplifies the load transfer mechanism and hence, making analysis easier.

References

{{reflist Civil engineering Bearings (mechanical) Bridge components Architectural elements