Step 6. Construct Vertical Bracing
Nineteen 8-foot long 6 x 6’s will be used for the main center support columns. (Detail 6.1) At the top of each column, drill one ½ inch hole through the column. This hole should be 1 ¾ inches from the top of the column, centered horizontally. At the bottom of each column, nail a 1 foot by 1 foot, ¾ inch thick sheet of plywood. Place the column in the centerline trench and move the column to the rear side of the 4 x 6 top crossbeam. The top of the column should be flush with the top of the crossbeam. If it is not flush, adjust the height of the main support column by adding or removing granular soil from the bottom of the centerline trench. With the drill hole facing the top cross beam, clamp the two beams together. Using a long 3/8 inch drill bit, place it through the hole in the column and drill into the crossbeam approximately 3 inches . Place a ½ x 9 hex lag screw through a ½ inch washer, a ¾ inch washer, the main support column and screw it into the top cross beam. Remove the clamp. Place a level on the sides of the main support column and adjust the levelness by moving the column.
Repeat this step for all 19 of the 4 x 6 top support beams.
Fill the remaining 6 inches of the centerline trench with granular soil and compact down.
Run two continuous headers (2 x 8) from the front to the rear of the shelter. One on each side of the main support columns. With the exception of the shelter ends, the header boards should always terminate in the middle of the main support columns. The header boards may have to be cut to accomplish this. Push the header up until it is flush with the top crossbeam and nail the header to the main support column.