A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships. The word "superstructure" is a combination of the Latin prefix, super, (meaning above, in addition) with the Latin stem word, structure, (meaning to build or to heap up).
In order to improve the response during earthquakes of buildings and bridges, the superstructure might be separated from its foundation by various civil engineering mechanisms or machinery. All together, these implement the system of earthquake protection called base isolation.
Read more about Superstructure: Aboard Ships and Large Boats, Bridges