Design and Draw

siennatearfulUrban and Civil

Nov 25, 2013 (3 years and 9 months ago)

72 views

Competency: 304.00

Design and Draw
Foundation Plans

Objective: 304.02

Design footings, foundation walls, girders,
piers, ventilation, and slab floor/foundations.

Continuous Wall Footings

Footing Size


Engineering data regarding soil &
structural loads


NC Building Code minimum footing widths


Single story, conventional wood frame =
16”


Single story, brick veneer over wood frame
= 16”


Minimum Width of Concrete or Masonry
Footings
chart


Assumes soil with bearing capacity of
2000psf

Continuous Wall Footings

Footing Size


“Rule of thumb” based on thickness of
foundation wall


Width = 2 x foundation wall thickness


Depth = foundation wall thickness


Assumes firm, undisturbed soil or
engineered fill


Minimum soil bearing capacity of 2000 psf

Continuous Wall Footings

Steel Reinforcement


Controls tension forces


Two longitudinal rebars in bottom of
footing carry tensile loads


Prevents spreading


Tension forces occur only in bottom
portion of footing


Top portion of footing is in compression

Continuous Wall Footings

Steel Reinforcement


Bar size based on 1/8”


Example: #4 bar = 4/8” (1/2)


Transverse bars tied to longitudinal bars
at regular intervals


“Chairs” hold bars in place


Footing thickness to width ratios require
increases in widths, turn, thickness


Continuous Wall Footings

Steel Reinforcement


Stepped footings


Vertical and horizontal parts resembling
steps


Vertical step no more than ¾ the
distance of horizontal depth


Reduce excavation and materials costs
on hilly terrain


8” module used when concrete block is
used for foundation wall

Foundation Walls


NC Residential Building Code
determines
concrete & masonry wall thickness


Unbalanced fill


Height of earth pushing against foundation
wall


Wet soil produces greater pressure than dry
soil


Type of wall construction


Hollow


Solid


Grouted

Foundation Walls


Lateral resistance to earth pressures
provided by intersecting walls, floors,
and pilasters


Pilasters are posts built into a wall


Supports for beam endings and
resistance to pressure


Masonry units are interlocking with units
in alternating direction


May be filled with grout and/or steel
rebars

Foundation Walls


Poured concrete walls can be reinforced
with steel rebars placed in tension zone


Poured concrete walls can be tied to
poured concrete footings using “keys”
formed into footing


Foundation walls located in center 1/3
of footing


Extends minimum of 8” above grade
with wood construction

Foundation Walls


Minimum distance 7’
-
0” floor to ceiling in
a basement


Lintels


Structural members over openings in
masonry walls


4” minimum bearing


Steel or masonry

Foundation Walls

Damp Proofing


Heavy coats of tar or two coats of
cement based paint for basement walls


Thin coats of cement
-
mortar materials
or parging


Polyethylene or plastic sheeting


Thickness measured in “mils”


6 mil most common

Foundation Walls

Damp Proofing


Drain tile


4” perforated pipe surrounds structure at
bottom of wall


Set in washed gravel from wall


Covered with 6” washed gravel above


Holds back soil


Allows water to enter pipe


Water in pipe is carried away

Girders
-

Design


Based on material, span, and load


Live and dead loads included


Determine load area(s) requiring
support & multiply by sum of live and
dead loads


Determine loads imposed by walls and
significant features & add to area loads


Determine load per foot


Divide total load by length of beam

Girders
-

Design


Charts require load per foot of beam to
calculate beam size and span


Load expressed in “kips”


1 kip = 1000 lbs


Modifications


Increase number of piers/columns to
shorten span


Change material


Pier spacing remains equal


Change species/grade of wood

Girders
-

Design


Beam charts limit size based on
deflection


Deflection


amount of bending
occurring when structural member is
loaded


Limited to 1/360 of span

Girders


NC Residential Building Code

charts for
built
-
up wooden girders include pier &
footing sizes


Determine area supported by pier


Appropriate chart for single or multi
-
level
structure


Determine depth of structure


Determine interior or exterior girder


Select grad and species of lumber

Girders


Read size of pier & pier footing from
chart


Masonry pier height limited by size of
pier & type of construction


Interior and exterior piers treated
differently


Piers capped


4” solid masonry for single
-
story structure


8” solid masonry for multi
-
story structure

Piles


Driven into soil or onto bedrock without
separate footing


Supports heavy structures or those built
on poor soils


Used when footings cannot be
stabilized in loose soil


Beach homes built on loose sand

Piles


Materials


Treated wood


Steel pipes filled with concrete


Steel beams


Bored holes filled with reinforced poured
concrete


Pre
-
cast concrete

Foundation Ventilation


NC Residential Building Code

minimum
requirement is 1 sq. ft. ventilation for
every 150 sq. ft. crawl space area


Vapor barriers reduce ventilation
requirements

Slab Foundation


Reinforced concrete floor and footing


Monolithic pour


Footings may be poured separately


Requires less time and labor than T
-
foundation


Turned down extension extends below
frost line


Perimeter insulation

Slab Foundation


NC Residential Building Code

requirements


Vegetation, top soil, foreign material
removed


Below grade 4” slab poured on clean,
graded sand, gravel, or crushed stone


Vapor barrier between slab & sub
-
grade


Where no base course is used


Not necessary in unheated structure


4” minimum slab thickness

Slab Foundation


Concrete construction


Composed of cement, sand, stone or
gravel aggregate, and water


Varying ingredient amounts change
strength & properties


Cement composed of lime, silica, and other
materials


Purchased by cubic yard (3’x3’x3’ = 27 cu.
ft.)


Strength measured in PSI (pounds per
square inch)

Slab Foundation


Cures over a long period of time


Affected by temperature


Extreme cold slows curing


Extreme heat causes evaporation

Slab Foundation


Cracking


Expansion and contraction due to
temperature change


Moisture content


Large areas more likely to crack


Joints


Cut into fresh concrete with joining tool


Cut into cured concrete with masonry saw


Floor slabs not bonded to columns or walls

Slab Foundation


Cracking (cont’d)


Expansion joints positioned next to walls


Building felt or fiberboard used as
expansion joints


Fiberglass fibers may be used in mix
rather than steel


Wire mesh reinforces slab


Pre
-
manufactured control joints in slab


Pressure
-
treated lumber placed where
members abut concrete