How do bridges hold so much weight?

How do we know?

↻ One of the pages with a moving picture

Golden Gate Bridge cables are made of thousands of thin wires.

1. Bridges handle two big forces. Compression squeezes a material. Tension stretches it.
2. Press on a beam bridge and its top edge is squeezed while its bottom edge stretches. Beams rarely span over 250 feet.
3. An arch has great natural strength. Thousands of years ago, Romans built arches out of stone.
4. In a suspension bridge, the road and cars pull on the cables, so the cables are in tension. They can span 2,000 to 7,000 feet!

Both main cables of the Golden Gate Bridge hold about 80,000 miles of wire, enough to wrap around Earth more than three times! A loom-type shuttle laid the wires in 6 months and 9 days.

Each main cable holds 27,572 steel wires twisted together.

The bridge opened to walkers on 27 May 1937 and to cars on 28 May. Its longest span, 4,200 feet, was a world record.

Wow number

27,572 Steel wires twisted together inside each main cable of the Golden Gate Bridge.

Myth or fact?

Beam bridges can span thousands of feet. Myth. Beam bridges rarely span more than 250 feet.

Suspension bridges can span the farthest. Fact. They can reach 2,000 to 7,000 feet.

Think about it

Each cable is thousands of thin wires, not one giant rod. Why might many thin wires work better?

Where in the world?

Golden Gate Bridge, California, USA which opened to walkers on 27 May 1937 and to cars on 28 May. Its longest span, 4,200 feet, was a world record — 37.8199° N, 122.4783° W.

Where these facts come from

Every number on page 98, and who measured it

Has this changed?

How bridges hold weight is not going to change.

Records are “so far”. The Golden Gate’s span was a world record when it was built, and longer bridges have been built since.

Words from this page

compression

A force that squeezes a material.

tension

A force that stretches a material.

suspension bridge

A bridge whose road hangs from big cables.

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