MIL-DTL-16036M(SH)
3.5.3 Framework fabrication.
3.5.3.1 Standardized and special units. Framework shall be fabricated from angles, channels, or other structural
shapes, or formed members. Each edge of each unit shall be formed by a length of a structural shape, formed
member, or formed members welded to effect a continuous length. When formed members are used for structural
support, their strength shall be equivalent to that of structural members (angles, channels, and so forth) used for the
same application. Intermediate vertical supporting members shall be provided for the support of such heavy devices
as circuit breakers and large disconnecting switches and shall be constructed using structural members welded to the
bottom and top horizontal structural members. Gusset plates shall be continuously welded at the corners of the units
in both lengthwise and lateral vertical panels so that each corner shall have a strength not less than the bending
strength of the weakest adjoining vertical or horizontal member. Typical bottom corner construction is shown on
3.5.4 Gusset plates. In the special case where the lengthwise gusset plates at the front of the unit interfere with
devices, special consideration shall be given to the construction of the corner to provide maximum strength. Small
gusset plates or L-shaped plates may be used in the above special case. A gusset plate shall not be less than 1/8-
inch thick. Where the thickness of the gusset is less than 3/16 inch, the diagonal edge shall be bent to form a flange.
Three-sided forged or formed and heat treated aluminum alloy gussets may be used on aluminum constructed
switchboards. Typical gusset plates are shown on figure 11.
3.5.5 Framework assembly. Framework of each standardized unit or special section shall be stiffened to resist
bending by the use of diagonal braces or welded sheets, but braces and sheets shall not be secured in such a manner
as to restrict access to the front and rear of the units. The framework of each unit or section shall be fabricated by
welding all members except those which must be disassembled for replacement of devices. In these cases, bolting
shall be employed. Riveting shall not be used in the assembly. Interframe bolting of standardized units to form
sections shall be in locations as shown on figure 8. The minimum size of bolt used for this purpose shall be of 1/2-
inch diameter. Structural shapes that comprise the base members shall not be less than 1/4 inch thick and the
horizontal flanges which are bolted to the foundation shall be not less than 2 inches wide. Members in the top of the
frame of all switchboards shall have sufficient strength and rigidity for securing top braces. Braces shall not be
considered as part of the switchboard.
3.5.6 Foundation channels. Foundation channels shall be supplied with complete switchboard section or
sections.
3.5.6.1 Standardized units. (see 6.3.10) Foundation channels shall be drilled for the maximum number of
mounting holes as shown on the floor plan (see figure 8) regardless of whether they are used for the original
installation or not. Individual switchboard manufacturers may use all or any combination of these holes for
mounting as long as the shock and vibration tests of 4.4.3.3 and 4.4.3.4 are met. Where the thickness of the frame
member is less than 3/8 inch, a 1/4-inch thick reinforcing washer, approximately 2 inches square, shall be provided
under each bolt head.
3.5.6.2 Special sections. The frame of each section shall be bolted directly to the channel by 3/4-inch diameter
bolts conforming to MIL-DTL-1222. Bolt holes in channels shall be 0.813 (plus 0.010, minus 0.001) inch. The
minimum number of holding-down bolts to be provided for a section shall be based on the total weight of the
section, allowing 210 pounds for each 3/4-inch diameter bolt. No less than four bolts shall be provided per unit.
Holding-down bolts shall be located as near the vertical frame members as practicable, but with no more than 3
inches horizontal separation between the vertical member and the center of the bolt hole. Where more than 12 bolts
are required, two in each corner, and two adjacent in each intermediate vertical member, and the thickness of the
frame member is less than 3/8 inch, a 1/4-inch thick reinforcing washer, approximately 2 inches square, shall be
provided under each bolt head.
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