MIL-S-45152H
3.5.1 Load space. The usable load space of the platform shall be defined as follows:
(a) For type I level deck - Length from the rear of the gooseneck to the rear of the platform ahead of the tires
(b) For type II drop deck - Length from the rear of the gooseneck to the frame splices at
the kickup over the wheels
(c) For type V level deck extended - Length from the rear of the gooseneck to the rear
of the semitrailer.
3.6 Construction and stresses. Main frame members shall be adequately braced with a sufficient number of crossmembers to present a rigid construction with sufficient strength for the loads imposed. Except for type V level deck extended semitrailer, the outside frame members shall run the full length of the load space. The rear crossmembers on all types shall extend the full width of the semitrailer. When the semitrailer is loaded with rated payload, and with the loads distributed as specified in 3.3, the maximum fiber stress in each frame member(s) shall be not greater than 50 percent of the frame material yield strength or, when specified (see 6.2),
33 percent of the frame material yield strength. Under the above cited conditions of loading, the
main frame deflection shall be not greater than 2 inches. All parts of the framing shall be completely electric-arc welded. The strength of the finished welds shall be such that they will not fail or crack when the semitrailer is subjected to the loads and performance requirements
specified herein. On class B and class D folding gooseneck semitrailers, the underside, front and
top of the gooseneck, shall be furnished with high strength, low alloy materials providing abrasion and corrosion resisting qualities. For class B, C, D and E folding and detachable gooseneck semitrailers, the maximum fiber stress, in any of the gooseneck area components, shall be not greater than 25 percent of the component material yield strength, with the rated semitrailer payload applied during loading, traveling, and unloading operations.
* 3.6.1 Frame splices. Where frame members are spliced, joints shall be reinforced to fulfill the dynamic loading requirements of 3.3 through 3.4 and the static loading requirements of 3.6. Splices shall be designed to avoid stress concentration. Splice welds shall be continuous. Transition areas in the gooseneck and kickup shall be smooth and rounded to minimize stress concentrations.
3.6.2 Stress analysis. A stress analysis for the semitrailer, loaded as specified in 3.4, shall be performed. The stress analysis shall include shear and moment diagrams and deflection calculations. The strength of the floor, crossmembers, and outside frame members shall not be included in calculations to compute the main frame maximum fiber stress; but the weight of the floor, crossmembers, and outside frame members imposed on the main frame shall be included in the total load imposed on the main frame. Stress calculations shall include complete analysis of the gooseneck, kickup area, floor, crossmembers, and longitudinal frame members.
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