The length of the metal frameworks of bridges change when the temperature changes.
thermal expansion, linear thermal expansion, thermal motion, expansion, shrinkage, heating, bridge, bridge deck, temperature, metal framework, thermodynamics, tied-arch bridge, physics
Bridge expansion joint
Principle of thermal expansion
atom - Balls symbolise these. When the temperature increases, the thermal motion of atoms increases, they maintain a greater average separation. This results in an increase in volume.
When the temperature increases, solid bodies expand, while they contract when the temperature decreases. Thermal expansion is the result of a change in the motion of particles. As the temperature increases, the atoms oscillate with greater amplitude and the average distance between them increases.
The thermal expansion of solid bodies is greater when their original volume is greater, and when the change in temperature is greater. Thermal expansion also depends on the physical properties of materials.
Due to thermal expansion, the length of bridge support structures changes with changes in temperature. This must be taken into account when a bridge is being designed. The problem can be solved by placing roller bearings on one of the piers, thus permitting the horizontal movement of the superstructure. The expansion joint built into the bridge deck allows for continuous traffic over the bridge even in extreme thermal conditions in summer or winter.
In summer the bridge deck expands due to high temperature, while in winter it contracts. The change in length is directly proportional to the length of the bridge and the change in temperature, usually it is only a few centimetres. Without a roller bearing even these few centimetres would cause huge mechanical tension in the deck, which would result in serious damage to the metal structure of the bridge.