Paper craft · Challenge · about 45 minutes
Folded-Beam Paper Bridge
Uses scissors · Uses glue · Adult help suggested
- Card stock or printer paper printed with sheet 1 (two beam strips), 216 x 279 mm (8.5 x 11 in (Letter) or A4)
- Card stock or printer paper printed with sheet 2 (deck and test strip), 216 x 279 mm (8.5 x 11 in (Letter) or A4)
- Blunt-tip scissors
- Glue stick
- Ruler (to check the scale bar, crease and measure the gap)
- Two equal stacks of books
- Small, light test objects such as erasers, coins or paper clips
For the grown-up: Help set up two steady stacks of books on a table, and keep the test to small, light objects placed by hand.
Safety: Use blunt-tip scissors and cut away from your fingers.
Safety: This is a tabletop model: test it only with small, light objects, one at a time, and never lean on it, stand on it or load it with anything heavy.
Blue dashes: valley fold (toward you). Pink dash-dot: mountain fold (away from you). Thick line with scissors: cut. Yellow: glue.
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Start. Print both sheets at 100% (Actual size). Check that each 5 cm bar measures 5 cm.
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1. Cut: Cut out the two beam strips, the deck and the test strip along their solid outlines.
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2. Fold and unfold: Crease each beam strip along its four long dashed lines, bending the paper away from the printed side. Use a ruler for straight folds.
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3. Glue: Fold each beam strip into a square tube. Rub glue on its tab, press the tab inside the opposite edge and hold the tube flat until it sticks.
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4. Valley fold: Fold up the two red and white curbs of the deck along their dashed lines, so they stand straight up.
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5. Glue: Turn the deck upside down. Glue a beam along the underside next to each curb fold, then turn the bridge right side up.
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6. Place: Stand two equal stacks of books on a table with a 15 cm (6 in) gap between them. Measure the gap with your ruler.
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7. Check: First lay the flat test strip across the gap and set an eraser in the middle. The flat paper sags.
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8. Place: Take the strip away and lay your bridge across the gap, beams down. Set the eraser on the middle of the deck: the folded beams hold it up.
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9. Check: Test with small, light objects such as coins or paper clips, adding them one at a time. Count how many it holds, then compare designs.
If something goes wrong
- A beam springs open. Glue the whole length of the tab and hold the tube flat with a book on top for a minute.
- The bridge slides off the books. Make the gap 15 cm, no wider: each end of the bridge must rest about 2.5 cm on the books.
- The deck sags between the beams. Press the beams right next to the curb folds, or add a third beam down the middle.
- The bridge tips sideways. Center the load on the deck, and check that both beams sit flat on the books.