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<br /> <br /> <br />Figure 4.39 Elevated Foundation Loading <br /> <br />psf), snow (20, 30, 40, psf) or wind (15, 25 psf) is <br />shown in Tables 4.6 to 4.9. <br />Using these loads, the minimum horizontal <br />beam sizes shown in Table 4.17 must be used to <br />support the manufactured home and are based <br />on sawn timber having an allowable bending <br />stress (Fb> of 1250 psi, corrected for load dura- <br />tion, treatment, and service condition. Minimum <br />beam sizes are determined as follows: <br /> <br />P x e <br /> <br />Sx = <br /> <br />F' <br />b <br /> <br /> <br />Where: Sx = minimum section modulus of <br /> beam (in3) <br /> p = load from chassis I-beam (Ib) <br /> e = distance from chassis I-beam <br /> to horizontal beam/vertical <br /> member connection (assumes <br /> 15 inches from side of <br /> manufactured home to the <br /> center line of the vertical <br /> member) <br /> F' = allowable wood bending <br /> b <br /> stress (psi) corrected = <br /> 1207.5 psi <br /> 59 <br /> <br /> <br />Figure 4.40 Horizontal Support Beam <br /> <br />For the purposes of the horizontal beam capac- <br />ity and installation, the distance from the side of <br />the manufactured home to the center line of the <br />vertical member must not be more than 15 inches. <br />For instance, a 14 foot wide manufactured bome <br />located in a 20 psf roof live load and 25 psf wind <br />load area having chassis I-beams 75-1/2 inches <br />apart and longitudinal post spacings along the <br />manufactured home of eight feet, would require <br />four three-by 14-inch horizontal members between <br />each post running under the manufactured home <br />as shown in Table 4.17, Where other vertical <br />member spacings or wood having a different bend- <br />ing stress is used, the equation previously shown <br />can be used to calculate the minimum section <br />modulus needed, and the required timber size <br />determined. <br />Longitudinal beams placed above the horizon- <br />tal support beams as shown in Figure 4.41 can <br />provide additional support and will be needed if <br />the manufacturer requires perimeter supports for <br />the floor system. These transfer certain loads away <br />from the center of the horizontal support beam. <br />Where longitudinal beams are used the vertical <br />member capacity presented in Tables 4.13 to 4,16 <br />must be reduced by five percent. <br />