Paper craft

Folded-Beam Paper Bridge

Challenge (level 5 of 5)
45 min
9 steps
Ages 9–14 (a guide, not a rule)

Uses scissors
Uses glue
Adult help suggested

Start Making Print with template

A flat strip of paper sags under an eraser. Fold the same paper into a square tube and it becomes a beam that holds its shape, because the folded sides resist bending. This tabletop bridge uses two folded beams under a deck with curbs. Compare it with the flat test strip, then try small, light objects one at a time.

Before you start

You need

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). Print both sheets on the same kind of paper so the test is fair.
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

Decorating (optional): The beams and deck are printed. Name your bridge and write it on the curb, or draw lamp posts on the deck.

No card stock or printer paper printed with sheet 1 (two beam strips)? Two equal boxes or two blocks can replace the stacks of books. A third folded beam in the middle makes the bridge even stiffer.

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.

Use blunt-tip scissors and cut away from your fingers.

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.

How to place the paper before the first step — **Your paper:** Print both sheets at 100% (Actual size). Check that each 5 cm bar measures 5 cm.

Valley fold: blue dashes. Fold toward you, like a valley.
Mountain fold: pink dash-dot. Fold away from you, like a mountain.
Crease: a thin gray line where you folded before.
Cut: a thick solid line with scissors.
Glue: a yellow area marked "glue".
Turn over: flip the whole model to its other side.

Step by step

Each step shows what to do (left) and how it should look after (right).

Do this

Result

Step 1 of 9 Cut Cut out the two beam strips, the deck and the test strip along their solid outlines.
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Result

Step 2 of 9 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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Result

Step 3 of 9 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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Result

Step 4 of 9 Valley fold Fold up the two red and white curbs of the deck along their dashed lines, so they stand straight up. (The deck, printed side up, shown larger.)
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Result

Step 5 of 9 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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Result

Step 6 of 9 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. (Set the bridge aside: now the table for the supports.)
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Result

Step 7 of 9 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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Result

Step 8 of 9 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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Result

Step 9 of 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.

A paper bridge with gray folded beams and red and white curbs spanning the gap between two stacks of books, with an eraser on the deck.

You made it!

Yours may look a little different. That is part of making things by hand.

Print the steps

Template

Print the template at 100% (Actual size), not "Fit to page". Then measure the check bar with a ruler: it must be 5 cm (2 in) long.

Sheet 1: two beam strips · 184 × 206 mm. Each beam folds into a 19 mm (3/4 in) square tube, 200 mm long. Print at 100%.
Sheet 2: deck and test strip · 155 × 206 mm. The deck is 60 mm wide between its curbs. Print at 100%.

Print the template

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.

Helpful hints

A beam is stiff because its folded sides stand on edge: try bending a flat strip and a folded beam in your hands and feel the difference.
Change one thing at a time when you compare designs, such as the gap or the number of beams.

An original PlayOwl project.