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<br /> <br />CHAPTER IV <br /> <br />DESIGN OF ELEVATED FOUNDATIONS <br /> <br />This chapter provides information with which <br />elevation techniques discussed in Chapter III can <br />be evaluated to determine their ability to resist an- <br />ticipated loads. In addition, the chapter presents <br />an overview of flood-induced loads, tables of <br />calculated forces, governing design equations, <br />and specific technical information which can be <br />used to determine an appropriate elevated foun- <br />dation design for a manufactured home, <br />The capability to withstand flood-induced loads <br />depends upon not only the site design and struc- <br />tural capacity of the foundation, but also upon the <br />manufactured home itself, Therefore, it is critical <br />to assure that the design criteria under which the <br />manufactured home was constructed are not ex- <br />ceeded through the transferal of flood-induced <br />loads to the manufactured home itself, <br />The minimum design criteria for manufactured <br />homes required by the HUD's Manufactured <br />Home Construction Safety Standards (MHCSS) <br />are as follows: <br /> <br />Roof live load 40, 30 or 20 pounds per <br />square foot (pst) depending <br />upon anticipated location <br /> <br />15 or 9 psf depending upon <br />anticipated location <br /> <br />25 or 15 psf depending upon <br />anticipated location <br /> <br />Floor live load 40 psf <br /> <br />Dead Load 20 psf <br /> <br />The maps shown in Figures 4,1 and 4.2 <br />geographically depict the roof live load and wind <br />load zones, <br /> <br />Roof wind net <br />uplift <br /> <br />Wall wind load <br /> <br />ROOF LOAD ZONIlIl4AP <br />NQr1h.... ... 40 PS"(Snowj <br />MJddl. ..... . so per (SlltJW) <br />; SOl1U1 .. la PSt" {Mlnlmum) <br /> <br /> <br />Figure 4.1 Roof Live Load <br /> <br />WIND ZONE MAP' <br />Standard Wind Zone I 15 PSF Horl:ront..l 9 PSP' Uplift <br />HurrIcane ZOlle II 25 PSF Horizontal 15 PSP' Uplift <br /> <br /> <br />..... <br /> <br />..... <br /> <br />Figure 4.2 Wind Load <br /> <br />Generally, manufactured homes have the ability <br />to resist only a very limited range of flood forces <br />before the design capacity of the manufactured <br />home is e.x!;;eeded and significant damage results, <br />For example a nine to 12 inch floodwater differen- <br />tial between the inside and outside of an anchored <br />manufactured home can cause an upward floor <br />deflection, failure of the floor decking, and flood- <br />water inundation, <br />The technical information in this chapter in- <br />cludes consideration of the design capacity of the <br />manufactured home, Any foundation "over <br />design" would not improve the strength capabil- <br />ities of the manufactured home design, The foun- <br />dation system recommendations, therefore, are <br />compatible with the manufactured home design <br />criteria, <br />Each manufactured home siting situation will be <br />unique, The amount of information necessary to <br />provide specific technical guidance for all possi- <br />ble siting and flood loading situations would be <br />overwhelming, This chapter, therefore, provides <br />general guidance and technical information which <br />can be effectively used in determining the limits <br />of a particular candidate design. In this chapter, <br />example calculations are provided to assist in the <br />use of various design charts and tables, The user <br />is cautioned, however, that the examples provided <br />apply only to the specific conditions stated for each <br />design problem, Extrapolations from solutions pro- <br />vided for specific examples are not recommended, <br />As previously discussed, state regulations, <br />such as those shown in Figure 4.3, may require <br />design by a professional engineer. <br /> <br />33 <br />