Let’s look at the different types of bridges, how they work, and what makes them special.
Beam bridge
How It Works: A straight, flat bridge that is supported by columns or piers at both ends (and sometimes in the middle for longer bridges).
Best For: Short distances.
Materials Used: Concrete, steel, wood.
Examples: Simple highway overpasses, pedestrian bridges.
Fun Fact: The simplest type of bridge, and one of the oldest.
Famous beam bridge: King Fahd Causeway (Saudi Arabia to Bahrain).
With a length of 15.5 miles (25 km), this beam bridge was built in 1986 to link Saudi Arabia and Bahrain, allowing easy travel between the two countries.
Activity: Build a beam bridge (easiest)
Materials:
Cardboard strips or wooden popsicle sticks
Books or blocks (to use as supports)
Small weights (like coins or toy cars)
Instructions:
Place two books or blocks a few inches apart to act as supports.
Lay a strip of cardboard or popsicle sticks flat across the gap.
Test the strength by adding small weights (coins or cars) to see how much it can hold before sagging or collapsing.
Try making it stronger by adding more layers or supports underneath.
Lesson: Beam bridges work well for short distances but sag easily without extra support!
Arch bridge
How It Works: Uses a curved arch shape that transfers weight down and outward toward supports (abutments) at either end.
Best For: Medium distances.
Materials Used: Stone, brick, steel, concrete.
Fun Fact: Arch bridges have been built since ancient Roman times.
Famous arch bridge: Sydney Harbor Bridge (Australia).
With a length of 3,770 feet (1.149 meters), this arch bridge was built 1923 – 1932 in Sydney, Australia. It’s been nicknamed “The Coat hanger” due to its distinctive shape.
Activity: Build an arch bridge (moderate)
Materials:
Paper or cardboard
Books or blocks for support
Tape or glue
Instructions:
Cut the paper or cardboard into an arch shape.
Place the arch between two supports (books or blocks).
Test the bridge by placing weights on top.
Experiment by using multiple arches side by side for added strength.
Lesson: The curved shape of the arch helps distribute weight evenly, making it stronger than a beam bridge.
Suspension bridge
How It Works: A deck (road) is hung from long cables that are draped over tall towers. The weight is spread out and transferred to the towers and then down to the ground.
Best For: Very long spans (up to thousands of feet).
Materials Used: Steel cables, concrete, steel towers.
Fun Fact: Suspension bridges are some of the longest bridges in the world.
Famous suspension bridge: Golden Gate Bridge (USA).
With a length of 1.7 miles (2.7 km), this suspension bridge was built 1933 - 1937 to link San Francisco with Marin County. It’s painted orange to enhance its visibility in fog.
Activity: Build a suspension bridge (challenging)
Materials:
String or yarn
Paper or cardboard (for the deck)
Straws or skewers (for towers)
Tape or glue
Books or blocks (to act as anchor points)
Instructions:
Build two tall towers using straws or skewers.
Attach strings between the towers, letting them drape downwards like a suspension bridge.
Lay the deck (cardboard or paper) across the strings.
Secure the ends of the strings to the books or blocks.
Test the bridge’s strength by adding small weights.
Lesson: Suspension bridges are great for long distances because the cables spread the weight evenly to the towers and ground.
Cable-stayed bridge
How It Works: It’s similar to a suspension bridge, but instead of cables draping over towers, shorter cables go straight from the towers to the deck, forming a fan or harp-like pattern.
Best For: Medium to long spans.
Materials Used: Steel cables, concrete, steel towers.
Fun Fact: They are often mistaken for suspension bridges but are more modern and usually less expensive to build.
Famous cable-stayed bridge: Millau Viaduct (France).
With a length of 8,071 feet (342 meters), this cable-stayed bridge was built 2001 – 2004 to cross the Tarn River Valley in France. From the base of the valley to the top of the tallest pylon it’s 1,125 feet (343 meters) tall, making it the tallest bridge in the world.
Activity: Build a cable-stayed bridge (challenging)
Materials:
String or yarn (for cables)
Cardboard or paper (for deck)
Straws or skewers (for towers)
Tape or glue
Books or blocks (for support)
Instructions:
Build two tall towers using straws or skewers.
Attach strings from the towers directly to different points of the deck.
Secure the ends of the strings to the deck and the towers.
Test the bridge with weights to see how well the cables hold up the deck.
Lesson: Cable-stayed bridges use cables attached directly to the towers for strength and stability.
Truss bridge
How It Works: Uses a framework of triangles (trusses) to spread out the weight evenly. Triangles are super strong and prevent the bridge from bending or twisting.
Best For: Short to medium spans.
Materials Used: Steel, iron, wood.
Fun Fact: The triangles in truss bridges make them very strong and durable!
Famous truss bridge: Quebec Bridge (Canada).
With a length of 3,238 feet (987 meters), this cantilever truss bridge was built 1904 - 1917 to cross the St. Lawrence River near Quebec City in Canada. It has the longest cantilever truss span in the world at 1,800 feet (549 meters).
Activity: Build a truss bridge (challenging)
Materials:
Popsicle sticks or straws
Glue or tape
Paper or cardboard (for deck)
Weights (coins, toy cars)
Instructions:
Build triangles using popsicle sticks or straws. (Triangles are really strong.)
Connect the triangles into a long bridge structure.
Place the deck (cardboard or paper) across the truss frame.
Test the strength by adding weights.
Lesson: The triangles in truss bridges are very strong and can hold heavy loads without breaking.
Cantilever bridge
How It Works: Built using structures that stick out horizontally and are balanced on piers. The middle section (called a span) is often placed last.
Best For: Medium spans.
Materials Used: Steel, concrete.
Fun Fact: They look like giant diving boards sticking out over water.
Famous cantilever bridge: Forth Bridge (Scotland).
With a length of 8,094 feet (2,467 meters), this cantilever truss bridge was built 1882 - 1890 to cross the Firth of Forth to connect Edinburgh with Fife in Scotland. The Forth Bridge was designated a UNESCO World Heritage Site in 2015 for its innovative design and engineering significance.
Floating bridge (pontoon bridge)
How It Works: Rests on water using large, flat, floating structures called pontoons.
Best For: Short distances across calm water.
Materials Used: Steel, concrete, wood.
Fun Fact: Pontoon bridges have been used for thousands of years. The ancient Persians and Romans built temporary pontoon bridges for military purposes.
Famous pontoon bridge: Evergreen Point Floating Bridge (USA).
With a length of 7,710 feet (2,350 meters), this pontoon bridge was built in 2016 to cross Lake Washington to connect Seattle with Medina, Washington State, USA. It holds the Guinness World Record for being the longest floating bridge in the world.
Activity: Make a floating bridge (pontoon bridge) (easy)
Materials:
Plastic bottle caps, foam blocks, or pool noodles (pontoons)
Popsicle sticks or cardboard (deck)
Tape or glue
Basin of water
Instructions:
Place the pontoons (bottle caps or foam blocks) in the water.
Lay the deck (cardboard or popsicle sticks) across the pontoons.
Test the bridge by adding small weights (coins or cars).
See what happens when you remove or add more pontoons.
Lesson: Pontoon bridges float on water and are great for calm areas where a permanent bridge would be too expensive.
