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好久没听了、、、开学各种忙。。。
高中生你伤不起呀~!
good morning, class.
,today I have brought in a picture of a specific kind of bridge some pictures of
called a suspension bridgethat bridge.
That bridge looks
is familiar to me. Is it
is the Clinftonclift suspension bridge in Bristol,Bristle England.
Yes, you are right. You're really on the ball today.
can anyone tell me who built it and what is uniqueyou need about the suspension bridge?
Well ,the Clinfton Suspension Brdige was designed
well the suspension bridge were design in 1830
by a man named Brunel, pnow
but he died before the bridege was bridge finished.
as his memorial, the bridge was finally completed in 1864.
Excellent. You're
excellent,you really with it today. Now
now,who can tell me about suspension bridges? Or
is this question over your heads?head?
I think I can answer that.
according to some books I've have read about suspension bridges,
the road decks is hanging from cables that are strung across a rivers like the Avon Gorge in the picture. What makes
what make a suspension bridge unique .
need?
is that there is no support in the centre and the road deck hangs below the supports rather than resting upon them like other bridges
Excellent. Let me fill you in on some other details. Some of the oldest suspension bridges used ropes instead of cables that were loosely thrown across a gorge or river. This only allowed for people to hang as they crawled across. Soon after, wooden footways were added between the ropes. Unfortunately, these bridges were not convienent or safe for taking donkeys or carts across because of the swinging of the ropes and the loads were just too heavy for the bridge to bear. The suspension bridges that we use today, like the one in the picture, were first developed way back in the early 1800's.
Civil Engineers suchas Gelford and Brunel thought of the idea of using towers to lift up the cables and using a frame to support and stiffen the bridge called a truss. The tower allowedthe allow the bridge to stay perfactly flat,perfectly flag which would give horses and carriages a means to cross. across.in a nutshell, Brunel designed the ?? design for first non-none moving bridge. Today, the today the design of the suspension bridge is the same, but we use steel cables instead of iron links like those found on a of bicycle chain. In fact, Brunel'sB??'s famous bridge still has the iron chains links.
how do the suspension bridges hold the heavy weightway of cars and trucks? in the past they only used to
horses and carriages carriges.so the bridges didn't carry as notcarry much weight as they do now.
good point. all modern bridges that you see today use huge steel cables to hold the roadway. These the cables are hunghang over two towers and held by concrete blocks at both ends of the bridge. vehicles such as cars and trucks push down on the roadway and because the roadway is held upthem by hangers0 from the steel cables, they can transfertransform all the weightway onto the two towers. this means that the two towers are always compressed, which allows them to transfer the forces tofrom the ground or concrete blocks where they absorb the tension attention
from the steel cables. Steel is the preferred material used in long suspension bridges because it can handle extremely heavy weight. steel is stronger than ironthe air and isit also light in weight. A famous example can be seen on the Brooklyn Bridge in New York, USA.
Are there any problems with a suspension bridge?
I'm gladI'd like you asked me that question. there have been a couple of disasters in regard to the suspension bridges. If the engineers design athe bridge
that is too light or too flexible, ,
the bridges wil
will not be strong enough. They will begin to move and rock back and forth, even in light winds and will eventually collapse into the gorge or river below. |
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