A superstructure is an element of a structure that projects above the baseline. In the case of a building, it is generally the portion of the building located above ground, in contrast with the basement and substructure underground. For boats, it is the area above the main deck. There are a number of engineering concerns to weigh when designing and building the superstructure.
Designing superstructures requires considering the pressure and force they will exert on the finished construction and balancing this to address concerns about safety and stability. The size of the superstructure is an important factor in base design, as the base of the structure must be able to support the entire laden weight. In building construction, there may be concerns about structural integrity in earthquakes and high winds, and a technique known as base isolation may be used to reduce strain.
The superstructure is also the highly visible part of a structure. It needs to be clad in protective materials to keep the interior of the structure protected from the weather and may also be decorated to make it more visually interesting. Ornamental skins can be used to cover the cladding and it may be painted with stripes, logos, and other devices. Periodic inspections are conducted to make sure the structure is still sound, checking for issues like the development of rust, holes, and other issues.
As the most visible part of something, superstructures can have symbolic, as well as practical, value. Aesthetic concerns may be of importance to designers and owners, as the superstructure is the public face of a bridge, ship, building, or similar construction project.
Engineers working on new designs may consider the use of a variety of materials, weighing the risks and benefits of different construction materials against each other. Strong, light materials are usually sought out, as they will provide structural support without adding too much to the overall weight. Other issues can concern topics like opacity to radar, ability to withstand temperature extremes, and so forth.
Sometimes, the bulk of a structure is located below the base, rather than in the superstructure. Underground facilities, for example, tend to have a very small superstructure. Likewise, something like an aircraft carrier usually has a small superstructure for the control tower and observation deck, with the bulk of the facility being located underneath the main deck, including materiel storage, housing for personnel, fuel bunkers, and so forth.