24 CFR § 3280.903 - General requirements for designing the structure to withstand transportation shock and vibration.
(a) General. The manufactured home and its transportation system (as defined in § 3280.902(f)) must withstand the effects of highway movement such that the home is capable of being transported safely and installed as a habitable structure. Structural, plumbing, mechanical, and electrical systems must be designed to function after set-up. The home must remain weather protected during the transportation sequence to prevent internal damage.
(b) Testing or analysis requirements. Suitability of the transportation system and home structure to withstand the effects of transportation must be permitted to be determined by testing, or engineering analysis, or a combination of the two as required by paragraphs (b)(1) and (2) of this section.
(1) Road tests. Tests must be witnessed by an independent registered professional engineer or architect, manufacturer's IPIA or DAPIA, or by a recognized testing organization. Such testing procedures must be part of the manufacturer's approved design.
(2) Engineering analysis. Engineering analysis methods based on the principles of mechanics and/or structural engineering may be used to substantiate the adequacy of the transportation system to withstand in-transit loading conditions. As transportation loadings are typically critical in the longitudinal direction, analysis should, in particular, provide emphasis on design of longitudinal structural components of the manufactured home (e.g., main chassis girder beams, sidewalls, and rim joists, etc.). Notwithstanding, all structural elements necessary to the structural integrity of the manufactured home during in-transit loading are also to be evaluated (e.g., transverse chassis members and floor framing members, etc.).
(A) The summation of the design loads in paragraphs (b)(2)(i)(A)(1) through (3) of this section may be used to determine the adequacy of the chassis in conjunction with the manufactured home structure to resist in-transit loading:
(1) Dead load, the vertical load due to the weight of all structural and non-structural components of the manufactured home at the time of shipment.
(2) Floor load, a minimum of 3 pounds per square foot.
(3) Dynamic loading factor, (0.25)[(b2iA) + (b2iB)].
(B) However, the in-transit design loading need not exceed twice the dead load of the manufactured home.
(ii) To determine the adequacy of individual longitudinal structural components to resist the in-transit design loading, a load distribution based on the relative flexural rigidity and shear stiffness of each component may be utilized. For the purpose of loading distribution, the sidewall may be considered to be acting as a “deep beam” in conjunction with other load carrying elements in determining the relative stiffness of the integrated structure. Further, by proper pre-cambering of the chassis assembly, additional loading may be distributed to the chassis, and the remaining loading may be distributed to each of the load carrying members by the relative stiffness principle.
(iii) The analysis is also to include consideration for:
(A) Location of openings in the sidewall during transport and, when appropriate,
provisions for reinforcement of the structure and/or chassis at the opening.
(B) Sidewall component member sizing and joint-splice analysis (i.e., top and bottom plates, etc.), and connections between load carrying elements.
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