Suspension bridge facts for kids
The 1915 Çanakkale Bridge on the Dardanelles strait in Turkey, connecting Europe and Asia, is the suspension bridge with the longest main span in the world.
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| Ancestor | Simple suspension bridge |
|---|---|
| Related | Underspanned suspension bridge; see also cable-stayed bridge |
| Descendant | Self-anchored suspension bridge |
| Carries | Pedestrians, bicycles, livestock, automobiles, trucks, railed vehicles |
| Span range | Medium to long |
| Material | Steel rope, multiple steel wire strand cables or forged or cast chain links |
| Movable | No |
| Design effort | medium |
| Falsework required | No |
A suspension bridge is a special kind of bridge. Its main part, called the deck (where cars and people go), hangs from strong cables. These main cables stretch between tall towers. Smaller, vertical cables, called suspenders, connect the main cables to the deck. This design helps the bridge carry the weight of traffic and itself. Suspension bridges are known for their long spans and often don't need temporary supports during construction.
The main cables are securely fastened into the ground at each end. This makes sure all the weight pulling on the cables is held firmly. Sometimes, the bridge deck goes straight from a cliff to the main part. Other times, there are smaller sections of the bridge leading up to the main towers.
Contents
- The Story of Suspension Bridges
- How Suspension Bridges Are Built
- Different Kinds of Suspension Bridges
- Forces on a Bridge
- Other Uses for Suspension Principles
- How Suspension Bridges Are Built (Step-by-Step)
- The World's Longest Suspension Bridges
- Other Famous Suspension Bridges
- Learning from Bridge Collapses
- See also
- Images for kids
The Story of Suspension Bridges
Suspension bridges have a long and interesting history. The very first ones were simple ropes stretched across deep gaps. Sometimes, a walking path was laid directly on the ropes. Other times, it hung below them.
Early Designs
Long ago, people used clever ways to cross rivers and canyons.
- Tibetan Chain Bridges: Around the year 1433, a Tibetan builder named Thangtong Gyalpo started using strong iron chains for his bridges. He built many of these in Bhutan. His bridges used chains for both the railings and the walking path.
- Inca Rope Bridges: The Inca people in South America also built amazing rope bridges. These bridges were made from woven plant fibers. One famous Inca rope bridge, Queshuachaca, is still rebuilt every year by local communities!
The First Modern Suspension Bridges
The idea of modern suspension bridges began to take shape in the early 1800s.
- James Finley's Design: In 1801, James Finley in Pennsylvania, USA, built what's considered the first modern chain suspension bridge. It had a deck that hung from chains, just like today's bridges.
- Famous Early Bridges: Soon after, many chain bridges appeared in Europe. The Union Bridge (1820) in the UK was a big step. Then came the Menai Bridge (1826) in Wales, which was very important for its time.
- Beautiful Designs: Bridges like the Clifton Suspension Bridge (completed in 1864) in England and the Széchenyi Chain Bridge (opened in 1849) in Budapest, Hungary, showed how strong and beautiful these chain bridges could be.
Stronger Wire Cables
As engineers learned more, they started using strong wire cables instead of chains.
- Early Wire Bridges: The first wire-cable bridge was a small footbridge in Pennsylvania in 1816. Later, Marc Seguin in France built a temporary wire bridge in 1822.
- Permanent Wire Bridges: The first permanent wire-cable bridge was built by Guillaume Henri Dufour in Geneva in 1823.
- John A. Roebling: A very important engineer, John A. Roebling, used wire cables to build impressive bridges. He built a famous double-decker bridge over Niagara Falls in 1855.
- Modern Designs: The Manhattan Bridge in New York City, opened in 1909, is a great example of a modern wire-cable suspension bridge. Its design helped inspire many other long bridges around the world.
- Early Suspension Bridge Designs
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Drawing of the Tibetan-built Chaksam bridge from 1430, showing chains and suspender ropes.
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View of the Chain Bridge invented by James Finley Esq. (1810).
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Sagar Iron Suspension Bridge, India, built 1828–1830.
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Wire Bridge at Fairmount (1842).
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How Suspension Bridges Are Built
Main Parts of a Suspension Bridge
A suspension bridge has several key parts:
- Two tall towers or pillars.
- Two large suspension cables that stretch between the towers.
- Four anchors in the ground to hold the main cables tight.
- Many smaller suspender cables that hang down from the main cables.
- The bridge deck where traffic travels.
Suspension vs. Cable-Stayed Bridges
Cable-stayed bridges and suspension bridges look similar but work differently.
- Difference between types of bridges
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Suspension bridge
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Cable-stayed bridge, fan design
- Suspension Bridges: The main cables hang between the towers and are anchored to the ground. These cables carry most of the bridge's weight. Smaller cables connect the main cables to the deck.
- Cable-Stayed Bridges: In these bridges, the towers themselves are the main load-bearing parts. Cables run directly from the towers to different points on the bridge deck. The towers push the weight down into the ground.
Why Engineers Choose Suspension Bridges
Suspension bridges offer many benefits:
- Longest Spans: They can cross longer distances than almost any other bridge type.
- Less Material: Sometimes, they need less material, which can lower building costs.
- Easy Waterway Access: Construction often doesn't block the water below, so ships can still pass.
- Earthquake Resistance: Their flexible design can help them handle earthquake movements better than very stiff bridges.
- Future Upgrades: It's possible to replace deck sections to make lanes wider or add paths for bikes and walkers.
Challenges of Suspension Bridges
There are also some challenges:
- Wind Vibrations: Engineers must design them carefully to stop the deck from shaking too much in strong winds.
- Heavy Trains: They are not ideal for very heavy trains because their decks are not as stiff as other bridge types.
- Initial Access: Some access from below might be needed to install the first cables or lift deck parts.
Different Kinds of Suspension Bridges
Underspanned Bridges
In an underspanned suspension bridge, the main cables hang completely below the bridge deck. They are still anchored to the ground. This type is less common because the deck is not as stable as when it hangs from above.
Types of Suspension Cables
- Older Bridges: Main cables in older bridges were often made from chains or linked metal bars.
- Modern Bridges: Today, cables are made from many strands of strong wire rope. This makes them much stronger and more reliable. If a few strands break, the whole cable is still safe. It's also easier to build these wire cables in mid-air.
Deck Structures
Most suspension bridges use open truss structures to support the road. This helps prevent problems like those seen with the Tacoma Narrows Bridge (1940) collapse. Since the 1960s, new designs using shallow box girders have been developed. These designs help the bridge handle wind better.
Forces on a Bridge
Every bridge experiences three main types of forces:
- Dead Load: This is the weight of the bridge itself.
- Live Load: This includes the weight of traffic (cars, trucks, people) and normal weather like temperature changes, rain, and wind.
- Dynamic Load: These are stronger environmental forces, such as sudden strong gusts of wind or earthquakes.
Engineers must consider all these forces to make sure a bridge is safe and strong.
Other Uses for Suspension Principles
Suspension bridge ideas are used for more than just big road bridges.
- Footbridges: Light cable suspension can be a good choice for walking or cycling bridges. They can be less expensive and look very elegant. The Nescio Bridge in the Netherlands is a great example.
- Building Connections: If a bridge connects two buildings, the buildings themselves can act as the anchors for the cables.
How Suspension Bridges Are Built (Step-by-Step)
Building a large suspension bridge is a huge project! Here are the main steps:
- Foundations: First, engineers prepare the ground for the towers. This might involve sinking large concrete boxes (caissons) into the water or digging deep foundations on land.
- Towers: Next, the tall towers are built. They are usually made from strong reinforced concrete or steel.
- Saddles: Special devices called "saddles" are placed on top of the towers. These will hold the main suspension cables.
- Anchorages: Huge anchorages are built into the ground at each end of the bridge. These will hold the main cables tightly.
- Catwalks: Temporary walkways, called "catwalks," are built between the towers. These help workers install the main cables.
- Spinning Cables: High-strength steel wire is pulled across the catwalks, strand by strand, to form the thick main cables. Once all the strands are in place, they are compressed into a tight cylinder and wrapped.
- Suspender Cables: At specific points along the main cables, "cable bands" are installed. From these bands, the vertical suspender cables hang down.
- Deck Sections: Large sections of the bridge deck are then lifted into place and attached to the suspender cables. This is often done from the towers outwards.
- Finishing Touches: Finally, things like lighting, handrails, painting, and paving are added to complete the bridge.
The World's Longest Suspension Bridges
Suspension bridges are often ranked by how long their main span is. Here are some of the longest:
| Bridge | Country | Length | Year |
|---|---|---|---|
| Çanakkale 1915 Bridge |  Turkey |
2023 m (6637 ft) | 2022 |
| Akashi Kaikyō Bridge |  Japan |
1991 m (6532 ft) | 1998 |
| Yangsigang Bridge |  China |
1700 m (5577 ft) | 2019 |
| Xihoumen Bridge | China |
1650 m (5413 ft) | 2009 |
| Great Belt Bridge |  Denmark |
1624 m (5328 ft) | 1998 |
| Osman Gazi Bridge | Turkey |
1550 m (5085 ft) | 2016 |
| Lee Sun-shin Bridge |  South Korea |
1545 m (5069 ft) | 2012 |
| Runyang Bridge | China |
1490 m (4888 ft) | 2005 |
| Fourth Nanjing Yangtze Bridge | China |
1418 m (4652 ft) | 2012 |
| Humber Bridge |  United Kingdom |
1410 m (4626 ft) | 1981 |
| Yavuz Sultan Selim Bridge | Turkey |
1408 m (4619 ft) | 2016 |
Other Famous Suspension Bridges
Here are some other important suspension bridges:
- Union Bridge (England/Scotland, 1820): The oldest suspension bridge still carrying road traffic.
- Roebling's Delaware Aqueduct (USA, 1847): The oldest wire suspension bridge still in use in the United States.
- John A. Roebling Suspension Bridge (USA, 1866): Once the longest wire suspension bridge in the world.
- Brooklyn Bridge (USA, 1883): The first steel-wire suspension bridge.
- Bear Mountain Bridge (USA, 1924): The first suspension bridge to have a concrete deck. Its building methods helped create even bigger bridges.
- Benjamin Franklin Bridge (USA, 1926): Held the record for the longest span for a short time.
- Golden Gate Bridge (USA, 1937): A world-famous bridge in San Francisco, California. It was the longest suspension bridge for many years.
- Mackinac Bridge (USA, 1957): The longest suspension bridge between its anchorages in the Western Hemisphere.
- Si Du River Bridge (China, 2009): One of the highest bridges in the world, with its deck about 500 meters above the river.
- Rod El Farag Axis Bridge (Egypt, 2019): Holds the Guinness World Record for the widest suspension bridge in the world.
Learning from Bridge Collapses
Engineers learn important lessons from every bridge project, especially from those that face problems.
- Broughton Suspension Bridge (England, 1831): This iron chain bridge collapsed because soldiers marched across it in step. The rhythmic marching caused the bridge to vibrate too much. After this, the British Army ordered troops to "break step" when crossing bridges.
- Silver Bridge (USA, 1967): This bridge had a design that made it hard to inspect for damage. When it collapsed, it led to new laws requiring regular inspections and maintenance for older bridges.
- Tacoma Narrows Bridge (USA, 1940): This bridge was famous for swaying and twisting in the wind. Its design made it vulnerable to strong winds, which caused it to collapse just months after it opened. This event taught engineers a lot about how wind affects bridge designs.
- Kutai Kartanegara Bridge (Indonesia, 2011): This bridge collapsed due to construction problems and poor maintenance. It showed how important it is to build bridges correctly and keep them in good repair. The bridge was later rebuilt with a different design.
- Jhulto Pul (India, 2022): This pedestrian bridge collapsed, leading to a tragic loss of life. Investigations into such events help engineers understand how to prevent similar accidents in the future.
See also
In Spanish: Puente colgante para niños
- Cable-stayed suspension bridge
- Floating cable-stayed bridge
- Floating suspension bridge
- List of longest suspension bridge spans
- Timeline of three longest spans—Whether bridge, aerial tramway, powerline, ceiling or dome etc.
- Steel bridge
Images for kids
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The wooden 1808 Burr Suspension Bridge in Schenectady, NY, US, during demolition in 1871.
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Marc Seguin suspension bridge near Annonay, 1825.
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Squibb Park Bridge, Brooklyn, built 2013.
 | Roy Wilkins |
 | John Lewis |
 | Linda Carol Brown |
