Expansion joints at bridges
Cantilever expansion joint
Temperature changes and traffic loads can lead to the length of larger bridges fluctuating by about a metre. A so-called "expansion joint", which can expand and contract, is therefore installed at one end. Various expansion joint constructions have been developed during the course of time.Cantilever expansion joints, also called expansion joints with saw-tooth plates, have been used for about 100 years. If made using the conventional construction method they are, however, only suitable for expansions of up to approximately 300 millimetre.
In the 50s and 60s, bridge builders used supported expansion joints for large expansions of over 500 millimetre. On one side they consist of several plates which are connected to each other via joints. On the other side they are covered by a sliding support. Expansion lengths between those for which supported expansion joints and cantilever expansion joints are used are bridged using so-called supported expansion joints with one sliding support. In contrast to the other supported expansion joints these only require one plate on either side.
Modular expansion joint
Cantilever expansion joints, supported expansion joints with one sliding support and supported expansion joints are not watertight. Watertight modular expansion joints were therefore developed; these keep the water away from the substructure. By having many modular expansion joints lying next to each other and joined to each other with rubber-neoprene expansion profiles, this type of expansion joint can be used to bridge expansions of more a metre. The profiles are also used for smaller expansions of 65 millimetre and above.
Expansion joints made of asphalt are suitable for small expansions of up to about 40 millimetre. These joints can only be recognised in the road pavement by a practised observer: at the point where the bridge meets the road there is a strip of material which is usually of a different colour from the adjoining pavements. This bituminous body, which is modified with plastics, is supported on the underside by a metal plate.
Expansion joint made of asphalt
People living near bridges are often disturbed by the noise generated at expansion joints. Beneath the bridge, abrupt impact noises can often be heard when vehicles go over the expansion joint. Above the level of the bridge the surface of a modular expansion joint, which is like a wash-board, causes a series of shrill staccato noises. The noise below can be muted by the so-called "encasing" of the joint. Noise reduction upward can be achieved, for instance, by welded rhombus elements or finger transitions.