MAJOR BUILDING SYSTEMS

                                                 MAJOR BUILDING SYSTEMS
The simplest building system consists of only two components. One component is
a floor, a flat, horizontal surface on which human activities can take place. The
other component is an enclosure that extends over the floor and generally also
around it to provide shelter from the weather for human activities.
The ground may serve as the floor in primitive buildings. In better buildings,
however, the floor may be a structural deck laid on the ground or supported above
ground on structural members, such as the joist and walls in Fig. 1.1. Use of a
deck and structural members adds at least two different types of components, or
two subsystems, to the simplest building system. Also, often, the enclosure over
the floor requires supports, such as the rafter and walls in Fig. 1.1, and the walls,
in turn, are seated on foundations in the ground. Additionally, footings are required
at the base of the foundations to spread the load over a large area of the ground,
to prevent the building from sinking (Fig. 1.2a). Consequently, even slight improvements
in a primitive building introduce numerous additional components, or subsystems, into a building.
      More advanced buildings consist of numerous subsystems, which are referred to
as systems in this book when they are major components. Major subsystems generally
include structural framing and foundations, enclosure systems, plumbing,
lighting, acoustics, safety systems, vertical-circulation elements, electric power and
signal systems, and heating, ventilation, and air conditioning (HVAC).
Structural System. The portion of a building that extends above the ground level
outside it is called the superstructure. The portion below the outside ground level
is called the substructure. The parts of the substructure that distribute building
loads to the ground are known as foundations.
Foundations may take the form of walls. When the ground under the building
is excavated for a cellar, or basement, the foundation walls have the additional task
of retaining the earth along the outside of the building (Fig. 1.1). The superstructure in such cases is erected atop the foundation walls.

FIGURE 1.1 Vertical section through a one-story building with basement shows location
of some major components. (Reprinted with permission from F. S. Merritt and J. Ambrose,
‘‘Building Engineering and Systems Design,’’ 2d ed., Van Nostrand Reinhold, New York.)