An expansion joint system is simply a transition across an expansion joint opening.
In other words, it is a cover, a bridge or an insert. It may be a simple cover plate, engineered system, insert or even a compression seal.
Many systems, however, are engineered to fulfill a variety of additional functions.
Some of these functions include:
Fit a predetermined opening size.
Absorb building movement, thermal or seismic.
Be compatible with various surface finishes.