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Chapter 17 Constructing Structures
Setting Foundations
The foundation is the most impor-
tant part of any building project. This part
serves as the feet of the building. Try to
stand on just your heels. You will be unsta-
ble and wobble. Likewise, a building with-
out a proper foundation settles unevenly
into the ground. Such a building leans,
becomes unstable, and might collapse. The
Leaning Tower of Pisa in Italy is an exam-
ple of a building that has a poor founda-
tion. Over time, the tower has settled and
is leaning several feet to one side.
A complete foundation has two parts:
the footing and the foundation wall. See
Figure 17-8. The footing spreads the load
over the bearing surface. The bearing sur-
face is the ground on which the foundation
and building will rest. This can be rock,
sand, gravel, or a marsh. Each type of soil
offers unique challenges for the construc-
tion project.
The type of foundation to use is selected
to match the soil of the site. See Figure 17-9.
Three types are the following:
Spread foundations. These types
of foundations are used on rock
and in hard soils, such as clay. The
foundation walls sit on a low, flat pad
called a footing. On wide buildings,
posts support the upper floor between
the foundation walls. These posts also
rest on pads of concrete called footings.
Slab foundations. These types of
foundations are used for buildings
built on soft soils. They are sometimes
called floating slabs. The foundation
becomes the floor of the building.
Such foundations allow the weight of
the building to be spread over a wide
area. This type of foundation is used
in earthquake areas because it can
withstand vibration.
Figure 17-8. The foundation wall and footing spread the building’s weight onto the
bearing surface. The concrete foundation shown in the photo has been insulated to
reduce heat loss.
Foundation
wall
Footing
Wall
Floor joist