Bridges are built over roads, rivers, or railways. They appeared a long time ago. Back then, they were built with stones, ropes and logs(原木). Some were very simple, like a footbridge (人行桥) made out of a big tree. . This is because we have better technology today.
Bridges are a mix of maths, physics, design, and architecture(建筑). They are designed by skilled engineers and they take years to build.
Bridges must be strong enough to support not only their own weight, but also the weight of the people and vehicles(交通工具). They must last a long time and be built in a way that protects them from earthquakes, strong winds, and freezing.
. Let's take a closer look at each one.
Arch (拱) bridges were invented a long time ago by the Romans. They were built out of stone or brick(砖).
Beam bridges are horizontal (水平的) beams supported by many columns. . These bridges are very old as well, and people used stone and trees to build them.
Suspension bridges have a tower (索塔) on either side. The towers are connected by cables. They are more modern, with the first ones being built in the early 19th century.
The oldest bridge in the world is the Zhaozhou Bridge in China. But if you're looking for one of the most beautiful and famous bridges, it would be the Golden Gate Bridge in San Francisco. It's a suspension bridge built in 1937. It has is 2. 78 kilometers long. If you think that's long, you should see the Danyang-kunshan Grand Bridge in China. It's over 164. 85 kilometers long!.
A. It's an arch bridge made out of stone that was built in 605A. D. (公元）
B. The three main types of bridges are arch, beam and suspension.
C. The present London Bridge is more than 100 feet wide.
D. But today, bridges are bigger, stronger and more modern.
E. The columns (柱子) take the weight of the people and vehicles passing on the beam.
F. It's the world's longest bridge
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