Building Design and Construction Handbook - Merritt - Ventech!

FIGURE 1.2 Commonly used foundations:
(a) foundation wall on continuous footing; (b)
individual spread footing for a column; (c) pile
footing for a column.
BUILDING SYSTEMS 1.11
The footing under a wall (Fig. 1.2a)
is called a continuous spread footing.
A slender structural member, such as a
column (Fig. 1.2b), usually is seated on
an individual spread footing. When the
soil is so weak, however, that the spread
footings for columns become very large,
it often is economical to combine the
footings into a single footing under the
whole building. Such a footing is called
a raft, or mat, footing or a floating
foundation. For very weak soils, it generally
is necessary to support the foundations
on piles (Fig. 1.2c). These are
slender structural members that are
hammered or otherwise driven through the weak soil, often until the tips seat on
rock or a strong layer of soil.
The foundation system must be designed to transmit the loads from the superstructure
structural system directly to the ground in such a manner that settlement
of the completed building as the soil deflects will be within acceptable limits. The
superstructure structural system, in turn, should be designed to transmit its loads
to the foundation system in the manner anticipated in the design of the foundations.
(See also Sec. 6.)
In most buildings, the superstructure structural system consists of floor and roof
decks, horizontal members that support them, and vertical members that support
the other components.
The horizontal members are generally known as beams, but they also are called
by different names in specific applications. For example:
Joists are closely spaced to carry light loads.
Stringers support stairs.
Headers support structural members around openings in floors, roofs, and walls.
Purlins are placed horizontally to carry level roof decks.
Rafters are placed on an incline to carry sloping roof decks.
Girts are light horizontal members that span between columns to support walls.
Lintels are light horizontal beams that support walls at floor levels in multistory
buildings or that carry the part of walls above openings for doors and windows.
Girders may be heavily loaded beams or horizontal members that support other
beams (Fig. 1.3).
Spandrels carry exterior walls and support edges of floors and roofs in multistory
buildings.
Trusses serve the same purposes as girders but consists of slender horizontal,
vertical, and inclined components with large open spaces between them. The
spaces are triangular in shape. Light beams similarly formed are called openweb
joists (Fig. 1.6d).
Floor and roof decks or the beams that support them are usually seated on loadbearing
walls or carried by columns, which carry the load downward. (The horizontal
members also may be suspended on hangers, which transmit the load to