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<br />If, for example, one foot of water depth flowing <br />at six feet per second were anticipated, the drag <br />force would be 45,75 pounds per foot of length, <br />As the water velocity increases, the drag force <br />will increase significantly because of the V2 term <br />in the equation, In the above example note that <br />a doubling of velocity from six fps to 12 fps yields <br />a drag force four times as great or 182,98 pounds <br />per square foot of impacted area, <br />Drag forces due to water impacting the <br />manufactured home can impose a significant in- <br />crease in the loads on an elevated foundation, For <br />this reason the manufactured home must be <br />elevated above anticipated flooding, In addition, <br />drag forces will affect any manufactured home <br />foundation enclosure and transfer the drag forces <br />to the elevated foundation. Provisions for allow- <br />ing water to flow under the manufactured home <br />should, therefore, be employed to reduce drag <br />forces, In some higher velocity situations, any <br />manufactured home foundation enclosure should <br />be designed to break away before the forces cause <br />overloading or failure of the elevated foundation <br />system, <br />Another important consideration is the dif- <br />ference in height of the water upstream and <br />downstream of the manufactured home, Water <br />height will be greater on the upstream side; subse- <br />quently, the buoyancy and lateral fortes will be <br />greater on the upstream side, This imbalance of <br />forces on the manufactured home will create a <br />tendency for the manufactured home to overturn <br />as shown in Figure 4,10, <br /> <br />~ <br /> <br /> <br /> <br />'. <br /> <br />Figure 4.10 Overturning <br /> <br />The difference in height between the upstream <br />and downstream side of the home is dependent <br />upon water velocity and the position of the <br /> <br />manufactured home in relation to flow, If the <br />manufactured home is placed parallel to the flow <br />as shown in Figure 4,11, the drag forces are re- <br />duced due to a smaller area being exposed to flow, <br />thereby reducing the tendency for the manufac- <br />tured home to overturn, <br /> <br />"'1 <br /> <br />Figure 4.11 Parallel to Flow <br /> <br />If the manufactured home is placed perpen- <br />dicular to flow, the area of the manufactured home <br />affected by the flow, as shown in Figure 4,12, in- <br />creases as do the resulting drag force and the <br />height differ'entiai between upstream and <br />downstream flow, <br /> <br /> <br />Figure 4.12 Perpendicular to Flow <br /> <br />Due to lack of data available on height differen- <br />tial related to flow velocity, manufactured home <br />size and position in relation to flow, no specific <br />calculations or design techniques can be offered, <br />If, however, the manufactured home is elevated <br />such that floodwaters are not expected to reach <br />the manufactured home, any tendency to over- <br />turn will be eliminated. It is important to note, <br />however, that an elevated manufactured home <br />must be anchored to the elevating foundation or <br />ground to prevent overturning from wind. <br /> <br />38 <br />