In 1841 Squire Whipple patented a bridge which would be more stable than the bridges of that time; his secret was to use diagonal rods and to make the bridge wider near its ends. He analyzed his design and found that the weight on the bridge put the vertical pieces in compression and the diagonals only under tension. This is perfect for cardboard and duct tape.
Duct Tape is extremely strong under tension, so it will be used for the diagonal pieces.
Cardboard is made many ways; corrugated cardboard usually is stronger under compression along one axis, and is relatively easy to bend otherwise. This design will use the cardboard so that it is aligned to handle the compression.
Components of the Whipple Truss Bridge:
Arch Truss pieces (a)
Vertical pieces (v)
Diagonal pieces (d)
Horizontal pieces (called ties by Whipple) (T)
Flooring (not shown)
Knife (box cutter, kitchen knife, X-acto knife, etc.)
Scissors (for cutting duct tape cleanly)
Pen or pencil (the pen didn't draw on greasy cardboard well)
Step 1: Arch Pieces
Step 2: Drawing the Arch Pieces
These pieces were drawn onto cardboard:
(2) 11.25 x 2 inch rectangles (a)
(4) 10.75 x 3.4 inch rectangles (b)
(4) 8.75 x 4.5 inch rectangles (c)
(4) 11.5 x 6 inch rectangles (d)
A lot of 1.5 inch wide cardboard for the U parts of the arch
A lot of 1 inch wide cardboard for the vertical pieces
Step 3: Making the Sides
After making the first side of the bridge without them, and seeing how unstable it looked, I made the second side like Whipple designed it. How should I know about mechanical engineering; I'm an electrical engineer.
Step 4: Assembled Arch Segment
Step 5: Assembled Arch 1
Note that the vertical pieces are just straight pieces of cardboard, shoved through holes in the top arch segments. In this picture they have not been cut to a reasonable size to make an arch shape.
Step 6: Assembling Arch 2
Step 7: Tape Diagonals
Notice also that the arch segments have been placed on some horizontal ties, which have been duct taped together.
Flooring has also been placed between the two arches.
Step 8: Finished Bridge
Many thanks to Gene, Nick, and Gary for their assistance cutting out all the pieces of cardboard.