Bearing (statics)

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Beam on two support bearings ( supports ); left: fixed position r; right: floating bearing
The support on the tips of the triangular symbols (sometimes provided with additional small circles) indicates that the bearing does not counteract torques , i.e. allows rotations.

In terms of statics , bearings are connections between a rigid body ( supporting structure ) and its environment, with the help of which the body's movements are restricted. The force variables emanating from the bearing that counteract the forces and moments of the body are called bearing reactions .

Bearings that connect two bodies or structures to one another are called joints .

A bearing that counteracts all force values ​​is called a restraint . When using several bearings, the individual bearing i. d. Usually only forces, not absorbing moments. A distinction is made between fixed bearing ( fixed bearing ) and floating bearing (movable bearing). The former prevents movement in all directions. With a floating bearing, movements in one or two of the three directions in space are not prevented. Most of the time, the floating bearing only takes the weight of the body and can move horizontally.

Storage types

Fixed and movable clamping

A fixed clamping or only constraint is that bearing which displacements in all three directions as well as rotations around all three axes prevents the bearing point.

A floating bearing on the central pillar of a railway bridge. The track rests on steel rollers and can be moved.

A movable restraint is a plain bearing which allows displacements (mostly in one or two directions), but none of the three rotations in the bearing point.

Fixed bearing (fixed bearing) and floating bearing (movable bearing)

See also: Fixed-lot storage (mechanical engineering)

A fixed bearing prevents all shifts and enables one or more rotations in the bearing point.
In order to prevent the latter, a body must be stored in at least one other place on the plane and in at least two other places in the room.

A floating bearing - other common names are slidable support or sliding bearing - prevents one or two shifts (including mostly the shift due to the weight) and allows the other shifts and one or more rotations in the bearing point.

The terms fixed and floating bearings are mostly used in conjunction. One of the ball or plain bearings of a rotatably mounted shaft is designed as a fixed bearing to prevent the shaft from shifting. If the other bearings were also designed as fixed bearings , a change in temperature would result in an axial restraint due to the thermal expansion of the shaft. If all other bearings are designed as movable floating bearings, they allow the shaft to expand freely along its axis. Fixed and floating bearings are used in bridge construction for the same reason.

In other areas of structural engineering , it is often advantageous to provide a statically determined structure through the appropriate arrangement of fixed and floating bearings , as this is usually easier to calculate and is not subject to unexpected or undesired deformation in the event of thermal expansion.

2D storage types symbols

The three most common symbols in level support systems:

The circle at the top of the triangles symbolizes a swivel joint .

Fixed and floating bearings with a joint are also referred to as immovable or movable joint bearings .

See also

Individual evidence

  1. Structural Analysis 1 - Joints , In:; accessed in March 2020
  2. a b Sigurd Falk: Bending, buckling and swinging of the multi-span straight beam . In: Abhandl. Braunschweig. Knowledge Ges . tape 7 , 1955, pp. 74-92 ( [PDF]).
  3. a b Bernd Markert : Mechanics 1, stereostatics, statics of rigid bodies. Aachen 2014, pp. 73–77.