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APPENDIX C FOUNDATION CAPACITIES TABLES APPENDIX C
FOUNDATION CAPACITIES TABLES
C-100. USE OF FOUNDATION
CAPACITIES TABLES.

C-100.1. GENERAL. The Foundation Ca-
pacities Tables provide foundation design ca-
pacities and dimensions for three conditions of
foundation design.

A. Withdrawal Resistance. The ability
of a foundation wall or pier plus its respective
footing to resist uplift and overturning. See
Tables C-1 & C-2.

B. Vertical Anchor Capacity. The re-
quired size and spacing of anchors to tie the
superstructure to the foundation to meet the
required uplift or overturning in the transverse
direction. See Tables C-3 & C-4 (a & b).

C.

Horizontal Anchor Capacity. The
required size and spacing of anchors to tie the
superstructure to the foundation to resist slid-
ing in the transverse and longitudinal directions
- Horizontal Anchor Capacity Table, Table C--
5.
C-100.2. CONNECTIONS of the foundation
to the manufactured home is dependent on the
rated capacity of the manufacturer's connection
designs.
C-200. WITHDRAWAL
RESIS-
TANCE CAPACITY TABLES.
There
are two tables providing the withdrawal resis-
tance (uplift and overturning) for different de-
signs of foundation walls and piers on spread
footings at different depths.
C-200.1. LONGITUDINAL FOUNDATION
WALLS. The "Withdrawal Resistance for
Longitudinal Foundation Walls - Table C-1 is
used for manufactured homes anchored to lon-
gitudinal foundation walls, specifically system
type E. The table provides a footing width and
depth below grade to prevent uplift.
Example: Determine the withdrawal resistance
of a 6 reinforced concrete wall with a height
(hw) of 3- 4 and with a 6x16 footing. Re-
peat for a 6CMU wall grouted solid, then
grouted at 48 o.c., and lastly for an all-
weather wood foundation.
Solution: Start with the concrete wall:
wall weight: (0.5)
×(3.33)×150 pcf = 250 plf;
reinforced concrete footing weight:
(6
×16÷144in.sq./sq.ft.)×150pcf = 100 plf;
rectangular soil wedge wt: (3.33-1)
×((16×
6)
÷(2×12))×120pcf = 116 plf. The total
withdrawal resistance is the sum of the wall,
footing and soil block weight, which is
250+100+116 = 466 plf. This matches the ta-
bled value. The solid grouted CMU wall: wall
wt.: (3.33)
× (63 psf) = 210 plf, 16 footing
and 5 soil wedge calculations are the same as
above. The total withdrawal is the sum = 210 +
100 + 116 = 426 plf, just as found in the Table.
The partially grouted CMU wall: wall wt.:
(3.33)
×(45psf) = 150 plf, 16 footing and 5
soil wedge are the same. The total withdrawal
is the sum = 150+100+116 = 366 plf, just as
found in the table. Lastly, for the all-weather
wood foundation: wood stud wall wt.: 2x6
plate = 2.1 plf; (3)-2x4 plates = 3
×1.3 plf =
3.9 plf; 2x4@ 16 o.c. = 1.0 psf
× 3.33 =
3.33plf; 1/2plywood = 1.5psf
× 3.33 = 5.0
C - 1 plf. Wood sum = 2.1+3.9+3.33+5.0 = 14.3 plf;
footing weight is the same as caculated before.
Soil weight is based on a 6 wide wedge:
(3.33)
×(16-4)÷(2×12)×pcf = 140 plf. Total
withdrawal = 14.3+100+140 = 254 plf, just as
in the Table.
C-200.2. PIER FOUNDATIONS. The
"Withdrawal Resistance for Piers - Table C-2
is used for manufactured homes anchored to
piers; specifically system Types C, I, and Type
E when interior piers are used for anchorage.
This table also applies to the concrete tie-down
block for type C1 foundations.
Example: Determine the withdrawal resistance
of a 3 foot square footing with an 8x16 solid
grouted CMU pier of a height (hp) of 3-4.
Grade exists 12 inches down from the top of
the pier.
Solution: Assume the following material
weights: 8CMU = 84 psf; soil = 120 pcf; and
concrete = 150 pcf. Pier weight = (84psf)
×
(16/12)
× (3.33) = 373 lbs. Footing weight =
(150pcf)
×(8/12)×(3×3) = 900 lbs. Assume
footing perimeter creates a conservative shear
plane. Soil above footing also counted to resist
withdrawal. Soil Weight = (120pcf)
×(3.33-
1)
×(3
2
- (8)
×(16)/144) = 2267 lbs. Total with-
drawal resistance is the sum of the pier + foot-
ing + soil = 3541 lbs. This magnitude matches
the value found in the Table C-2.
C-200.3. FOOTING DEPTH. The bottom of
the footings must be below the maximum frost
depth for the area where the home is located.
Example: The average depth of frost penetra-
tion is 35 inches. Assume that the required
footing depth to resist withdrawal (Av) is
hw = 2 feet. The depth of the base of the foot-
ing is 24"-12"+6"=18". This is less than 35".
The depth of hw must be increased to 41" in
order for the base of the footing to be at 35"--
the required depth to prevent frost damage &
also satisfy withdrawal requirements (41"-
12"+6"=35").
C-300. VERTICAL ANCHOR CA-
PACITY TABLES
provide the required
anchor and reinforcing size and spacing to tie
the superstructure to the foundation wall or
piers. As in section C-200.1 above, there are
two Vertical Anchorage Capacity Tables, one
for longitudinal foundation walls and one for
piers.
C-300.1. PIERS. The Vertical Anchor Ca-
pacity for Piers - Table C-3 is used for manu-
factured homes anchored to piers to prevent
uplift specifically system Types C, I, and Type
E when interior piers are used for anchorage
(multi-section E's).
Example: Anchor bolts are assumed to be made
from A36 rod stock and of embedment length
sufficient to fully develop the allowable tensile
capacity (0.6
×F
y
) of the diameter of rod used.
A 1/2diameter anchor bolt has the following
capacity: (0.6
×36,000psi)×( × 0.5
2
/4) = 4,240
psi, as noted in the Table. The capacity of any
substituted grade of steel can easily be calcu-
lated if the yield point and diameter are known.
C-300.2. LONGITUDINAL
CON-
CRETE/MASONRY FOUNDATION
WALLS. The Vertical Anchorage Capacity
for Longitudinal Foundation Walls - Table C--
4A is used for manufactured homes anchored
to a continuous Reinforced concrete or rein-
forced concrete masonry foundation wall, spe-
cifically system Type E.
Example: Determine the anchorage capacity
per foot of foundation wall if 1/2 diameter an-
C - 2 chor bolts are spaced 3-4 o.c. and attach to a
continuous treated wood mud sill 1-1/2 thick.
Standard washers are used under the nut and
bear into the mud sill perpendicular to grain.
Solution: Determine the bearing area of a stan-
dard washer with O.D. = 1.375 and I.D. =
0.5625: A
brg
=
× (1.375
2
- 0.5625
2
)
÷ 4 =
1.237
sq. in.
. The capacity in bearing multiplied
by a bearing area factor C
b
= 1.25. Thus, the
bearing capacity = 1.237
× 1.25 × 565 psi =
873 lbs./ bolt. The capacity for a given spacing
of bolts is found by division of that spacing.
Thus, for a 3-4 bolt spacing: 873
÷ 3.33 =
262 plf, which is the same as in the Table.
Use of an oversized washer (for a 5/8 dia.
bolt) produces a larger capacity per bolt. The
O.D. = 1.75 and the I.D. = 0.6875, thus the
net bearing area : A
brg
=
× (1.75
2
- 0.6875
2
)
÷
4 = 2.03
sq. in.
. The vertical anchor capacity at
the same same spacing = 2.03
× 1.25 × 565 psi
÷ 3.33 = 431 plf, which is the same as in the
Table.
C-300.3. LONGITUDINAL
TREATED
WOOD FOUNDATION WALLS. The Ver-
tical Anchorage Capacity for Longitudinal
Foundation Walls - Table C-4B is used for
manufactured homes anchored to a continuous
treated wood foundation wall, specifically sys-
tem Type E. Vertical anchorage capacities are
based on the use of standard washers over 1/2
dia. bolts. Plywood thickness, nail size and
spacing are selected so as to provide equal or
greater capacity than the standard washer in
bearing. The APA Plywood Diaphragm Guide
was used to select plywood, and nailing re-
quirements for the Table.
Example: A 1/2 dia. bolt spaced at 3-4 o.c.
provides a vertical anchor capacity of 262
lbs./ft. This is the same capacity as found in
Table C-4A for a standard washer in bearing,
and its calculation is illustrated above. The
APA Table - Recommended Shear for Hori-
zontal APA Panel Diaphrapms requires for a
shear of 320 plf
> 262 plf: 8d COM nails @ 4
o.c. and uses 3/8 APA rated sheathing.
C-400. HORIZONTAL ANCHOR
CAPACITY TABLES FOR TRANS-
VERSE AND LONGITUDINAL
FOUNDATION WALLS
(Table C-5A &
C-5B) are used for all types of manufactured
homes: homes on continuous foundations -
Type E; homes on piers - Types C and I.
C-400.1. ASSUMPTIONS. Along with the
no