| Describe concrete foundations
a) Identify
poured in place foundations
b)
Describe footings
Footings are the wider base of
foundation walls which act like a snowshoe to distribute weight evenly
across a wider area than the foundation wall. This stops the foundation from
"digging in" or penetrating the dirt.
Photo of footings being framed, ready for pouring
of concrete
c)
Identify crawl space floor and foundation walls
Exterior Tee
Footings and crawl space
The components:
d)
Identify basement floor & foundation walls
Exterior Tee Footings and concrete slab on grade for basements
e)
Identify slab on grade floors
Floating Slabs On Grade - No crawl space or basements
These type of combined floor and foundation systems are economical but not
very often used in many areas where the water tables are high. Also they
are not practical for the climate conditions where the frost level dictates
that the footings must be several feet below the finished grade level.
However they are usable at the slab edges for non bearing walls.
f) Identify columns and pads
Columns
support and transmit concentrated loads.
A galvanized column shoe is embedded on the
top of the columns to provide the connection between the column and the
post. The footings are either square or rectangular in their shapes and the
size varies with the magnitude of the load versus the maximum bearing
capacity of the soil. For residential, they are usually 3'-0" square and
8" thick. The columns are 8”dia. 
g) Identify Re-bar
In foundation systems the footings are
designed to counteract two types of forces, compressive and tensile.
Although the concrete is strong in compression, it is relatively weak in
resisting tensile and shearing stresses that develop in structural members.
To overcome this lack of resistance steel bars are placed in the concrete
at the locations where the tensile stresses occur. The example of this is
the 'reinforced concrete footings'.
See Figure 5.
Assuming that the concrete footing bends in
the same direction as the forces acting on it, the top surface of footing
is compressed while the bottom surface is stretched or subjected to tensile
deformation. That is where the reinforcing bars are placed, Figure 6.
In the cases of slabs resting on solid ground
where the stresses are all compressive, the reinforcing is omitted
entirely. However, there is the light gauge steel mesh which is placed at
the mid thickness of the concrete slabs on solid ground. The main purpose
of this is the equal distribution of the expansion or contraction of slabs
due the change of temperature. In residential construction, where the loads
are minimal, for two story houses the footings and foundation walls are
solid concrete with no requirement of reinforcing. This is usually under the
local jurisdiction and the requirements may vary from one municipality to
another.
Fig
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