FLOOD02929

• County: Statewide
• Community: na
• Basin: Statewide
• Title: Manufactured Home Installation in Flood Hazard Areas
• Date: 9/1/1985
• Prepared By: FEMA
• Floodplain - Doc Type: Educational/Technical/Reference Information

Figure 4.3 State and Local Regulations

A. FLOOD FORCES AND THEIR

APPLICATION

A manufactured home installation can be af-
fected by flood and wind-induced forces acting
directly on the manufactured home, and on its
elevated foundation system, This portion of the
manual introduces and applies various flood and
design forces to form the basis for the general
design guidance for elevated foundation tech-
niques presented in Section B of this Chapter,

Hydrostatic Forces
Hydrostatic forces are those caused by both free
and confined water occurring above or below
grade, These forces are equal to the product of
the water pressure and the area of the surface on
which they act. In addition, hydrostatic forces are
equal in all directions and act perpendicular to any
surface with-which floodwaters come in contact.
In the case of manufactured homes, hydrostatic
forces include lateral forces (those acting in a
horizontal direction), uplift or buoyancy forces
(those acting vertically upward), or a combination
of both as shown in Figure 4.4,

;; '/

, ,

r/

A
;/

~

/-

@
Figure 4.4 Horizontal and Vertical Forces

lateral Forces

The lateral force of water acting against the wall
of a manufactured home is related to the water's
depth and specific weight.
During a flooding condition, water against a
manufactured home creates a hydrostatic pres-
sure distribution as follows:

p = wxh

Where:

p = pressure in pounds per square foot
w = specifiC weight of water-S2.4 pounds
per cubic foot
h = distance in feet measured vertically
downward from the water surface to the
point of action

The resultant lateral hydrostatic force acting per
linear foot on the submerged portion of the
manufactured home is the total area of the
pressure distribution given by:

Fe = '12 pxh = 112 wxh2

Where:

Fe = lateral force in pounds per linear foot

h = distance in feet from water surface to
bottom of manufactured home chassis
I-beams

A triangular distribution based on the amount
of submerged area of the manufactured home
results, as shown in Figure 4,5, The lateral
hydrostatic force is assumed to act at a point 2h/3
down from the water surface. This force can be
significantly intensified if perimeter enclosures are
installed since the distance h isthen measured
to the bottom of the enclosure,

Figure 4.5 Lateral Forces

For example, if a manufactured home without
perimeter enclosures was submerged in water to
a point two feet above the bottom of the chassis
I,beams, the resulting lateral force would be 124,8
pounds per linear foot, For a SO-foot long manufac-

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