Modular joint systems represent the state-of-the-art approach to accommodating the large movements of long-span bridges.

Modular expansion joints consist of three main components: sealers, separator beams and support bars .
 
Sealers and separator beams form a watertight joint at the riding surface.

Separator beams often are extruded or rolled metal shapes and allow joining of the seals in series.

The separator beams are supported on support bars at frequent intervals.

The modular systems on the market today can provide maximum movements of about 4 feet.

Explanatory animation movie of Modular Expansion Joint

To Download an excellent paper titled A closer look at bridge expansion joints by  Martin S. Mcgovern - Click  Here This paper gives a good overview of the development of concepts of the expansion joints.