This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.
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Unit 12
Foundation Prints
Technical Terms
Auger cast pile
Basement plan
Caissons
Concrete masonry
units
Floating slab
construction
Footings
Foundation plan
Friction pile
Frost line
Grade beam
Keyway
Monolithic slab
Slab-on-grade
Steel pile
Waterproofing
Learning Objectives
After completing this unit, you will be able to:
•
Identify footings on a foundation plan.
•
Identify types of foundation support systems.
•
Identify various components of a foundation
system.
•
Recognize reinforcing steel on prints.
Once the building has been located on the
plot and the necessary site clearing and excavation is complete, work begins on the concrete
footings and foundation walls. The details of
construction for the footings and foundation walls
for residential-type construction are found on the
foundation plan (or basement plan).
The footings and walls must be carefully laid
out because the entire structure is built upon the
footings and foundation walls and depends on
their accuracy. To make print reading easier, this
unit explains how footings and foundations are
located, excavated, and constructed. Slab-ongrade floor construction is also discussed.
Footings
Footings are the “feet” upon which the entire
building rests, Figure 12-1. The sizes of the footings are shown on the foundation plan or on a
detail of the foundation wall. The footing size is
determined by architects and engineers, based
on the type of soil (determined by tests) and the
weight of the building. The load of the building
is transferred through the upper portion of the
Reinforcing steel
Section 4 Reading Prints
Footings are also required under columns.
These footings frequently are wider and thicker
than footings for foundation walls, because the
column loads are concentrated in one spot. See
Figure 12-2. Fireplace chimneys and similar
concentrations of weight also require larger
footings.
Footings are located using strings attached to
batter boards set back from the excavation. The
footings can be trenches cut into the floor of the
excavation, or they can rest on the excavation
floor. In the latter case, boards are used to form
the footing sides to the proper width and height.
Footings must rest on undisturbed earth
below the frost line, the deepest point to which
the ground will freeze in a given region. The local
building code will give the depth of the frost line,
and how far below it the bottoms of the footings
must be placed.
Steel reinforcing rods are placed in the footings. This is especially important when footings
must pass over earth previously disturbed due to
an earlier excavation. When a poured concrete
foundation wall is to be erected on the footing, the
Keyway for
poured wall
Reinforcing
steel
Column
Figure 12-1.
Footings are designed to carry the weight of the entire
building and to transfer that weight to the earth below.
Depth
structure down to the foundation walls onto the
footings and into the ground. There are many
types of foundation systems; this unit will cover
those listed below.
•
Footings and walls
•
Grade beams
•
Auger cast piles
•
Caissons
•
Steel H-piles
Square
Figure 12-2.
Footings for columns have a larger cross section than
wall footings. A square shape is normally used.
drawing may call for a keyway to be cast in the
footing to anchor the wall. Refer to Figure 12-1.
On a foundation plan, footings are shown as
hidden lines, Figure 12-3. The width of the
footing under the foundation walls and columns is
shown. Reinforcing rods are shown as dots in
sectional views. On elevation drawings, these
rods are indicated by long dashed lines. In addition, notes on the drawing and in the specifications must be carefully checked for details
relating to construction of the footings.
Foundation Walls
Foundation walls are the base of the building.
They transfer the weight of the building to the footings and to the ground below. Foundation walls
can be poured-in-place concrete or concrete
masonry units (concrete block). Poured-in-place
concrete is used where soil and weather conditions exert considerable side pressure on the
walls. Where feasible, the use of concrete
masonry units is an efficient way of constructing a
foundation wall, because no forms are required.
Usually, both poured and block walls are reinforced with steel rods.
Foundation walls and columns are shown as
solid lines on the foundation plan. The space
between the lines represents the material used.
Foundation walls and footings are shown as
hidden lines in elevation views, Figure 12-4.
A foundation wall section is shown in
Figure 12-5. The symbols used in the section
indicate the general type of material used.
However, these materials will be detailed in
notes on the drawing or in the specifications.
Fireplaces and chimneys are shown on the
foundation plan with appropriate dimensions.
Details are drawn to provide construction details,
Figure 12-6.
Unit 12 Foundation Prints
169
170
Section 4 Reading Prints
Concrete wall
Concrete wall flooring
Concrete column
Column footing
Wall beam spanning
wall footings
Top of footing elevation
TOF = 91′-4″
Top of footing elevation
TOF = 89′-4″
Pilaster
Footing steps
Figure 12-3.
Wall and footing partial foundation plan.
Figure 12-5.
A foundation wall section provides a detailed view of the footing and wall construction. Note the wider footing,
which indicates that this wall is being used as a retaining wall.
Grade Beams
Figure 12-4.
Elevation view of a residence, showing foundation wall and footing as hidden lines.
A reinforced concrete beam that spans from
footing to footing is called a grade beam. The
beam is formed on the ground, or formed by a
trench in the earth. It is typically used to span
over weak disturbed spots in the soil support
system. See Figure 12-7.
Unit 12 Foundation Prints
171
172
Section 4 Reading Prints
system on a drawing, you will see that there are
usually several auger cast piles clustered together.
They are topped with a pile cap to make the cluster
work as a total load system, Figure 12-8.
removed and the bottom of the caisson tested for
soil load capacity. After the hole passes inspection, a steel reinforcing cage is installed, and the
hole is filled with concrete.
Caissons
Steel Piles
Caissons are also drilled, and are usually
from 18″–72″ in diameter, Figure 12-9. Caissons
are drilled to design depth. The drill is then
A steel pile is a long H-shaped (H-pile) or
round (pipe pile) steel member that is hammerdriven into the earth. The pile is driven to a
PLAN VIEW
Building load
Column
Pile cap
Figure 12-6.
This sectional view of a fireplace provides the needed construction details and dimensions.
Auger cast pile
Piles and Caissons
Auger cast piles, caissons, and steel piles all
are used to transfer loads down through unsuitable
soil to more appropriate load carrying materials.
Pile socketed into rock
for support
A
Auger Cast Piles
Earth provides
the form for
the concrete
Figure 12-7.
A grade beam serves as a building support.
This type of foundation system is drilled with a
12″–14″ steel auger to the appropriate design
depth. While the drilling shaft is being raised out of
the hole, concrete is pumped down the shaft to fill
up the cavity. When you view an auger cast pile
B
SECTION VIEW
Figure 12-8.
Section and plan of auger cast piles. A—Friction pile. B—Pile drilled and socketed into rock.
Unit 12 Foundation Prints
173
Section 4 Reading Prints
foundation, the elevations will be given for various
parts of the system. For wall footings, the top of
the footing is given an elevation marked, for
example, as TOF = 91′-4″ and 89′-4″. Sometimes,
the bottom of the footing will also be marked as an
elevation. For auger cast piles, caissons, and
steel piles, the top of the pile cap (upon which the
structure is going to be built) is the elevation
given. All the information is defined in details and
schedules. Each engineer and project will have its
own special elevation designation system.
Become familiar with the plans early in the
preconstruction phase to work out any coordination problems.
Concrete or
steel column
Pile cap
(not always
required
with caissons)
Caisson
typically
18″ to 72″
in diameter
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PLAN VIEW
1/2″ expansion joint
Floating slab
4″ Gravel
Compacted fill or
undisturbed soil
Foundation wall
Footing
Figure 12-12.
A slab floor poured within the foundation walls.
Slab-on-Grade
Building
load
Concrete
pile cap
Suitable soil
support material
or rock
Rock
Soil
Figure 12-9.
Drilled concrete caisson.
Steel
H- piling
Soil resistance
is the primary
support
suitable support stratum or driven to friction
resistance of the soil (this type of pile is referred
to as a friction pile). A friction pile works on the
principle of frictional resistance on the sides of
the pile from the soil into which it has been
driven. When you look at this type of foundation
system on a drawing, you will usually see
several steel piles clustered together and
topped with a pile cap to make the cluster work
as total load system. See Figure 12-10.
A concrete slab poured at ground level is
called a slab-on-grade. Concrete slabs are used
as both basement floors and main floors.
Basement floors are poured after the footings and
foundation walls are in and sometimes, in residential construction, before the rough framing starts.
Floating slab construction uses a
monolithic slab (one continuous unit),
Figure 12-11. Another method of producing a
slab floor is to first pour the foundation walls to
floor height. Then, the area within the walls is
filled with soil and gravel. Finally, the floor is
poured within the walls, separated by an expansion joint, Figure 12-12.
Load-bearing walls over slab floors require a
thickened slab, Figure 12-13. These areas are
indicated by hidden lines and a note.
No. 3 at 12″ OC
both ways
PLAN VIEW
SECTION VIEW
Figure 12-13.
The slab is thickened to create a beam below loadbearing walls.
4″
Slab Reinforcement
Below
frost
Foundation Elevations
A critical part of starting a building properly is
constructing the foundation at the designed elevation. Elevations for a foundation are marked on the
foundation plan view. Depending on the type of
Masonry
ledge
Stirrup
Reinforcing steel
Gravel
8″
SECTION VIEW
4″
Compacted
fill or
undisturbed
soil
2 #4 Cont.
Figure 12-10.
Building foundation system using steel H-piling.
Figure 12-11.
A monolithic slab foundation.
4″
12″
A slab-on-grade is not considered a structural
slab, but can have reinforcement to assist in loadcarrying and resistance to cracking. Steel reinforcing rods or welded wire fabric are cast in the
concrete when a slab is subjected to drying
shrinkage. Reinforcement is also used when the
concrete slab is expected to be subjected to
tension due to the settling of a dirt fill or heavy
load. A typical note specifying welded wire fabric
Unit 12 Foundation Prints
175
or reinforcing rods in a concrete floor would read
as follows:
Test Your Knowledge
5″ thk. slab w/ 6 × 6 – W10 × W10 WWF OVER
Write your answers in the spaces provided.
ABC GRAVEL SUBBASE
______ 1. When a footing must be placed above
ground that has been disturbed, it
should be _____.
A. twice as thick as usual
B. twice as wide as usual
C. reinforced with bars
D. no different than usual
E. None of the above.
or
#4 @ 18″o/c EW OVER 4″ABC
Waterproofing
Foundations
Waterproofing of foundation walls is needed
in areas where soil and climatic conditions
demand protection from underground water.
Residential waterproofing can be done with a
variety of materials, but usually consists of
mopping the outside of the foundation wall with tar
or asphalt, Figure 12-14. Sometimes, a polyethylene sheet is applied over the tar. Drawings for a
foundation to be waterproofed will have a heavy
black line on the exterior wall with a note indicating
location. Also, the building specifications may
specify the exact material and process to be used.
A layer of crushed rock or gravel is laid below
the floor area. This layer is then covered with a
heavy plastic vapor barrier to keep the dampness
in the ground from transferring to the slab.
______ 2. On a foundation plan, footings are
shown as _____.
A. continuous lines
B. hidden lines
C. phantom lines
D. dotted lines
E. Footings are not shown on foundation plans.
______ 3. _____ rods are used to reinforce footings, slabs, and foundation walls.
A. Iron
B. Deformed steel
C. Aluminum
D. Tungsten
E. All of these are used.
______ 4. A(n) _____ is placed between a slab
and a wall.
A. air gap
B. roll of insulation
C. reinforcing bar
D. expansion joint
E. All of these are commonly placed
between a slab and a wall.
______ 5. Welded wire fabric is used to _____.
A. reinforce steel beams
B. protect basement windows
C. reinforce concrete slabs
D. protect welders from heat
E. None of the above.
Figure 12-14.
Tar being applied to a residential foundation wall for
waterproofing.
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Section 4 Reading Prints
______ 6. True or False? Footings are only
needed below the perimeter walls of
a building.
______ 7. True or False? The positions of footings are determined by stretching
lines between batter boards.
______ 8. True or False? The frost line is the
depth at which the ground is frozen
when the temperature is 25°F (–4°C).
______ 9. True or False? Normally, a column
footing is larger than a footing below
a wall.
______10. True or False? Foundation walls do
not allow water to pass through.
11. What are the five types of foundation systems described in this unit?
______________________________________________________________________
12. How does a steel friction pile support a load?
______________________________________________________________________
13. What is the purpose of the pea gravel around the foundation wall?
______________________________________________________________________
14. What does the term TOF indicate?
______________________________________________________________________
15. What is the purpose of the reinforcement in a slab-on-grade?
______________________________________________________________________
Unit 12 Foundation Prints
Figure 12-15.
Use with Activity 12-2. This is Sheet 2 of the footing and foundation print.
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