Residential Foundations

siennatearfulUrban and Civil

Nov 25, 2013 (3 years and 6 months ago)

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Residential Foundations


Mr. Johanson

Technology Education

Blue Mountain High School

Foundations


Purpose


Considerations


Types of Foundations


Shallow Foundations


Spread Footings


Strip Foundations


Slab
-
on
-
Grade and Thickened Slabs


Purpose of Foundations


Provide a
level
,
stable

surface to safely
support a building


Transfer building loads to soil


Anchor the building from wind, flood, and
seismic loads


Design Considerations


Loads from the structure


Allowable soil bearing pressure


Frost depth


Flood elevation


Drainage


Costs

Loads from the Structure

Foundations Must Resist


Dead Load



Weight of building


Live Load


Weight of occupants,
furniture, and equipment


Lateral Loads


Wind


Seismic activity


Flood

SOIL REACTIONS

Allowable Soil Bearing Pressure


Indicates the maximum pressure that a soil
may be designed to support


Typically presented in pounds per square foot
(psf)


Different types of soils have different
allowable soil bearing pressures



Soil Information


Local building department, codes, and
regulations


Preliminary information: USDA Web Soil Survey
http://websoilsurvey.nrcs.usda.gov


Local or state building codes


Soil testing/analysis


Site inspection and simple soil testing


Soil borings taken at proposed foundation
locations



Foundation Wall Thicknes

Table 9 Minumum Width of Concrete or Masonry Footings
(inches)
1

Load
-
Bearing Value of Soil (psf)



1,500

2,000

3,000


4,000

CONVENTIONAL LIGHT
-
FRAME CONSTRUCTION

1
-
story

12

12

12

12

2
-
story

15

12

12

12

3
-
story

23

17

12

12

4
-
INCH BRICK VENEER OVER LIGHT FRAME OR 8
-
INCH HOLLOW CONCRETE MASONRY

1
-
story

12

12

12

12

2
-
story

21

16

12

12

3
-
story

32

24

16

12

8
-
INCH SOLID OR FULLY GROUTED MASONRY

1
-
story

16

12

12

12

2
-
story

29

21

14

12

3
-
story

42

32

21

16

Frost Depth


Freezing of soil can cause heaving of
foundations


Heaving refers to the upward movement of a
foundation, sidewalk, or other structure


Silt or clay soils with a high water table are
highly susceptible to frost


Defense


Build base of foundation below frost depth


Provide frost protection for foundation



Frost Heave

Frost Depth Contour Map

Flood Elevation


Inundation by flood
waters should be
avoided


Damage to structure


Damage to contents


Height of floors is
dictated by building
codes and should be
above flood levels


Courtesy Federal Emergency Management Agency. Photographer
Dave Saville.

Flood Insurance Rate Map (FIRM)

Affordable Home Site

FIRM area available on the FEMA online Map Service at
http://msc.fema.gov

Base Flood Elevation

Drainage


Ground should be sloped away from the
building


Provide drainage pipe along continuous
foundations


Ground floor should be located 6"


8"
above grade


Common types are French or tile drain
systems

Drainage


8"

Types of foundations

Spread, Spot, or Pad Footing



A spot or pad or spread footing is
used to support a single point of
contact, such as under a pier or
post. it spreads the load over a
broad area which supports one (or
a few) loads. These footings are
typically a 2' by 2' square pad, 10"
to 12" thick, and made with
reinforced concrete rated to 3,000
to 5,000 pounds per square inch
(psi) in compression.




USES


Under piers or columns


PIER
(Concrete or
Masonry)

SPREAD
FOOTING
(Concrete)

COLUMN

LOAD

Continuous (Spread) Footing

A continuous spread footing is commonly
used to provide a stable base around the
entire perimeter of a structure by placing
a wide strip of reinforced concrete that
supports loads from a bearing wall.
Buildings with spread footings often
include interior spot footings. A spread
footing supports the weight (load) from
the exterior or foundation walls. The
footing thickness provides the strength
needed to support the weight. The wider
width of the footing base creates a large
area to transfer this weight to the ground
and to prevent settlement.


USES



Under foundation walls



For crawl space/basement

FOUNDATION
WALL
(Concrete or
Masonry)

STRIP
FOOTING

(Concrete)

Footing Options

Wall Sections

Interior Pier Sections

THICKENED
SLAB

WALL

SLAB
-
ON
-
GRADE

Slab
-
on
-
Grade

and Thickened Slab

Slab
-
on
-
Grade



Reinforced
concrete floor supported by soil

Thickened Slab


A slab on grade
with an integral footing created
by thickening the slab


USES


Shallow frost depth or when frost
protection is used (instead of
strip footing)

Review


Foundations Provide a
level
,
stable

surface to safely support a building


There are various design considerations
that need to be taken into account


Water


Frost


Soil


There are a variety of methods of
foundations