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<br />
<br />tion or increasing the embedment of the founda-
<br />tion supports should be considered,
<br />
<br />Rate-of-Rise is a measure of how rapidly water
<br />depths increase during flooding, A slow rise of
<br />floodwaters will allow seepage of water into a
<br />manufactured home thereby counteracting uplift
<br />forces.
<br />When floodwaters rise quickly, this balance may
<br />not occur in time, resulting in buoyancy or failure
<br />of the manufactured home floor, Rate-of-rise is
<br />also relative to the amount of warning time prior
<br />to flooding, This is important in planning for
<br />emergency evacuation and in determining the
<br />feasibility of emergency loss mitigation
<br />procedures,
<br />
<br />Duration of flooding is the amount of time from
<br />inundation of an area to the recession of flood-
<br />waters, Duration influences how long the manufac-
<br />tured home and its foundation will be subject to
<br />-~---hydrostaffi::an-d--h-ydrodynamTc pressures, the
<br />strength of soils and building materials, the degree
<br />of seepage, and the length of time that a struc-
<br />ture may be inaccessible,
<br />Frequency of flooding, the rate of recurrence'
<br />of floods at a particular location, is primarily a con-
<br />sideration in selecting the installation site,
<br />Repeated occurrences of flooding over time, even
<br />when a single event does not result in the total
<br />loss of a manufactured home, can produce a
<br />cumulative wear-and-tear effect on a typical in-
<br />stallation, Flood frequency data is useful in the
<br />design of foundation and elevating systems in that
<br />it is an essential element in formulating assump'
<br />tions as to how often these systems will be ex-
<br />posed to flood forces,
<br />
<br />Debris load, the amount and type of-debris car-
<br />ried by floodwaters, can result in significant im-
<br />pact forces against a structure,
<br />Debris can also adversely affect a structure by
<br />blocking channels and interfering with natural
<br />drainage thereby increasing the magnitude of
<br />other flood parameters, Ice poses significant
<br />debris hazards, particularly during early spring
<br />floods,
<br />Manufactured homes are especially vulnerable
<br />to damage caused by debris impact. In addition,
<br />typical foundations, such as unreinforced
<br />masonry, offer little resistance to battering from
<br />debris, An inadequately elevated and anchored
<br />manufactured home can itself become part of the
<br />debris load during a flood, Further information con-
<br />cerning flood parameters is shown in Appendix C.
<br />In addition to flooding, the manufactured home
<br />installation will be subjected to wind forces,
<br />sometimes occurring concurrently with flooding,
<br />thereby placing additional loads on the manufac-
<br />tured home and its foundation,
<br />
<br />WIND HAZARDS
<br />High winds, most notably in coastal and moun-
<br />tainous areas, will impose forces on a manufac-
<br />tured home and the structural elements of its foun,'
<br />dation, Damage potential is increased when the
<br />wind forces occur in combination with flood forces,
<br />In addition, as the manufactured home is elevated
<br />to minimize the effects of flood forces, the loads
<br />on the elevated structure itself, due to wind, are
<br />increased, Figure 2,5 shows annual extreme
<br />fastest wind speed 30 feet above ground for the
<br />1 DO-year mean recurrence interval.
<br />
<br />
<br />.-->.
<br />
<br />1
<br />j
<br />
<br />Figure 2.5 Wind Speed Map
<br />
<br />Wind forces exert pressure on a manufactured
<br />home and its supporting foundation, Structural
<br />components, such as walls and roofs, are affected
<br />by winds and are designed to withstand certain
<br />wind forces, Figures 2,6 and 2,7 illustrate these
<br />lateral forces and their results,
<br />
<br />
<br />,
<br />
<br />
<br />o:r:
<br />
<br />r~'~
<br />//~~
<br />
<br />Figure 2.6 Lateral Wind Force
<br />
<br />17
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