Magazines: Designs : Fully Framed

Civil War Field Fortifications

Magazines

Theoretical Designs

Fully Framed Magazines

Fully framed magazine chambers were generally preferred over all other chamber structures made from relatively light revetment and siege materials. Full frames were much stronger and could sustain the overhead burden of the covering mass much better while retaining sufficient surplus strength to enable the basic structure to withstand multiple shot and shell impacts on the covering mass without displacement of the frames. Structural strength imparted by closely laid frames also allowed heavier scantling or timber to be used in construction of the roof than was possible in less solid chamber structures. Depending on the manner in which the frames were planked, fully framed chambers stood a much better chance of excluding excessive moisture seeping through the chamber walls than other, more porous, revetment materials. Just as important, the regular rectangular shape of a fully framed chamber, with its vertical walls and horizontal floor and ceiling, produced more effective storage space than other types of chambers which required inclined slopes or sharply angled ceilings.

D. H. Mahan described the fully framed magazine presented in his work on field fortifications as a "cofferwork" which was constructed from six inch square scantling. The frames were composed of four members, a cap-sill for the top of the frame, two stanchions for the sides and vertical supports, and a ground-sill for the lower horizontal element of the frame which rested on the soil and carried the weight of the frame. These elements were cut long enough to allow an interior clearance of six feet high and six feet wide and were joined using simple nailed butt joints. The cap-sill was six feet long and connected to the interior faces of the stanchions, which were 6' 6" long and joined to the upper faces of the ground-sill which was seven feet long. A magazine constructed according to this design would require enough frames to cover its length in 2' 6" increments, the distance that was to left between frames. When the frames were set up (either free standing above ground level or sunken in a trench) 1' 6" thick planks, which would be held in place by the pressure of the soil surrounding the chamber, were used to line and connect the exterior faces of the frames. A flooring of planks would also be laid across the ground sills. Unlike other chamber structures in which the roof was formed of scantling joists laid latitudinally across the width of the chamber, the roofing material for this fully framed chamber would be laid across the tops of the cap-sill and would run slight beyond the full length of the chamber. The illustration of this chamber in Mahan's Treatise shows a roof composed of crossing layers of fascines in which the cap-sills also served as roofing joists. Like all the other magazine designs described by Mahan, the chamber was to be buried under a covering mass of soil to a depth of about three feet.

Duane's Manual offered a very sturdy sunken fully framed chamber that used strong mining frames that were joined for the specific purpose of bearing an overhead load. Duane's frame consisted of a cap-sill which measured 8" x 6" and was six feet long, two six inch square stanchions 5' long, and a 6" x 3" ground-sill which was 5' 6" long. The cap-sills and stanchions were joined with an overlapping notches that allowed the upper half of the cap-sill to remain intact and cover the tops of the stanchions, which made for a much superior joint to Mahan's simple butt joint that exposed the top ends of the stanchions. The lower end of the stanchions were notched to fit over the ends of the ground-sill which allowed the burden to fall on both the ground-sill and the stanchions, again, this joint was far superior to Mahan's lower joint which allowed the full weight of the chamber structure and covering mass to fall on the stanchions and converted the ground-sill into a simple spacer. When properly joined Duane's frame produced a rectangular interior space 4' 6" high and 5' 6" wide which was 1' 6" shorter than Mahan's frame and would have compelled troops in the chamber to bend at the waist, bringing on an extra bit of physical misery when handling heavy barrels of gunpowder.

Frames to form the chamber were set 2' 6" apart (from edge to edge) in a trench four feet deep and slightly over six feet wide. A lining of one inch thick planking was inserted between the exterior faces of the stanchions and the trench walls while six inch thick planking was nailed longitudinally across the cap-sills to form the roof. The roof was further strengthened with one or more layers of heavy timber or fascines. A two foot thick layer of soil which was shaped in the form a regular pitched roof or curved mound was thrown onto the chamber roof, rammed, and covered with a heavy tarpaulin. Another five of soil was added to form the shock absorbing covering mass.

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