Laserfiche WebLink
<br /> <br />tured home, this translates into nearly four tons <br />of pressure, <br />Table 4, t provides the total lateral forces and <br />point at which they act (center of gravity) for <br />various water depths, The shaded areas in the <br />table, corresponding to water column heights <br />greater than or equal to 12 inches, highlight where <br />these forces become overly excessive and exceed <br />the design capacity of a manufactured home, Con- <br />sequently, further elevation should be considered, <br /> <br />Buoyancy <br />In backwater or no-flow conditions, the critical <br />hydrostatic force on a manufactured home is buoy- <br />ancy which is dependent upon the difference in <br />water height inside and outside the manufactured <br />home as shown in Figure 4,6, As the manufac- <br />tured home is raised above grade, the flood depth <br />relative to the manufactured home floor elevation <br />will decrease, as will the buoyancy force, <br /> <br /> <br />Figure 4.6 Buoyancy Forces <br /> <br />Elevating the home above potential flood levels <br />is the only practicable method for eliminating <br />all anticipated buoyancy forces on the <br />manufactured home. <br /> <br />The buoyancy force is related to the weight of <br />water and height of water displacement and is <br />calculated as follows: <br /> <br />Fb <br />Where: <br />Fb <br /> <br />= w x L-.h <br /> <br />= Buoyancy force in pounds per <br />square foot <br /> <br />= Weight of water-62.4 pounds per <br />cubic foot <br /> <br />L-.h = Difference in height of water col- <br />umn inside and outside in feet <br /> <br />Buoyancy is equal to the weight of water times <br />the difference in water height outside and inside <br />the submerged surface, Water one foot above the <br />bottom of an unflooded manufactured home <br />interior would yield a buoyancy force of one foot <br />x 62.4 pounds per cubic foot or 62.4 psf as shown <br />in Figure 4,7, When the buoyancy force is greater <br />than the weight of a manufactured home, which <br />is approximately 20 pounds per square foot of floor <br />area, the capacity of a conventional anchoring <br />system is >exceeded and flotation can occur. In <br />view of these force considerations, manufactured <br />homes must be elevated above anticipated flood <br />levels, <br /> <br />w <br /> <br />Table 4.1 <br /> <br />LATERAL FORCES (F,t) , <br />(pounds per linear foot of home length) <br /> <br />Height of Water Colum (inches) <br /> <br />1 <br /> <br />2 <br /> <br />3 <br /> <br />4 <br /> <br />5 <br /> <br />6 <br /> <br />9 <br /> <br />F,t 0.22 0.87 1.95 3.47 5.42 7.80 17.55 <br />c 0.66 1.33 2.00 2.67 3.33 4.00 6.00 <br /> <br />F,t = 1/2 w x h2 Ob./lin. ft. of home) <br /> <br />Where: <br /> <br />w = 62.4 Ib./cu.ft. <br /> <br />h = height of water column in feet, and <br /> <br />12 <br /> <br />15 <br /> <br />18 <br /> <br />24 <br /> <br />30 <br /> <br />36 <br /> <br />48 <br /> <br /> <br />c = center of gravity in inches through which <br />F,t acts (2h/3) measured down from water surface. <br /> <br />35 <br />