Bridges Name ___________________________________________ Date __________________

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Arch Bridges Some of the oldest bridges in the world are arch bridges. The weight of such a bridge does not push straight down, but is carried along the curve of the arch to the end, where it is absorbed by special supports. The bridge must be built of materials that are strong under compression, because it must be able to support its own weight as well as the weight of cars and other traffic. Arch bridges were built of stone by the Romans over two and a half thousand years ago. Some of their bridges, such as the famous Pont du Gard aqueduct, still stand. This seems miraculous, because the Romans didn’t use mortar, but the bridges were so well constructed that they held themselves in place. Today, materials such as steel and concrete have replaced stone. Most modern arch bridges have a span of up to 800 feet, although there are some with a span over 1,500 feet. The problem with arch bridges is the process of construction. Since arch bridges are unstable until the span is completed in the middle, complicated scaffolding must be built under the bridge to prevent it from falling down. In some cases, this method has been replaced by using a system of cables, which do not block traffic under the bridge as scaffolding does.

1. Why doesn’t the weight of an arch bridge push straight down? a. Because it is built of special materials. b. Because there is scaffolding under the bridge to support it. c. Because with spans under 2,000 feet that doesn’t happen.

d. Because of the arch shape, which passes the weight along the curve.

2. Romans used ................. for building their bridges. a. stones and mortar b. adobe bricks c. stones without mortar d. steel and concrete

3. Arch bridges ............... . a. were only built by the Romans b. can have a span over 1,500 feet c. cannot have a span under 800 feet d. cannot have a span of over 1,500 feet

4. What kinds of problems might arise when constructing an arch bridge? a. Scaffolding used for the construction will block traffic below the

bridge. b. High velocity winds will be a threat to the bridge, because it is

very unstable. c. Cables used to support the bridge will block traffic below the

bridge. d. The bridge will become unstable after the span is completed in

the middle.

Bridges Name ___________________________________________ Date __________________

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Beam Bridges A beam bridge is the simplest kind of bridge. It is made up of two (or more) piers which support a horizontal beam. The weight of the beam pushes down on the piers, so it is necessary for the beam to be made of material that is strong enough to withstand compression on the top side and tension (stretch) on the bottom side. Pre-stressed concrete is usually ideal, because it can withstand both. It even has steel rods inside to reinforce it. Even better, it is also one of the cheapest materials used in construction. Nevertheless, not even concrete can be stretched forever: the longest span possible is about 250 feet. This does not mean there cannot be a longer bridge. Spans can be linked together, and the result is a ‘continuous span’ with many piers. The Lake Ponchartrain Causeway in Louisiana is 24 miles long and has two sections: one consisting of 1500 spans, the other of more than 2200. This type of bridge works well when it is necessary for the bridge to cross long distances, but a problem arises when the space below it is needed. In this case a beam bridge is not the best solution. 1. Beam bridges .............. . a. are a complicated kind of bridge b. are made up of piers and a beam c. do not have to be constructed of very solid materials d. are never constructed of concrete 2. Pre-stressed concrete ................. .

a. can withstand tension but not compression b. can withstand compression but not tension c. contains steel rods for reinforcement d. is usually rather expensive 3. Which of the following statements is false? a. Concrete cannot be stretched forever.

b. It is not possible for a beam bridge span to be longer than about 250 feet.

c. Spans may be linked together to form a continuous span. d. A beam bridge cannot be longer than 250 feet. 4. The Lake Ponchartrain Causeway .............. . a. is 48 miles long b. consists of 1500 spans c. is an example of a continuous span d. is not a good solution

Bridges Name ___________________________________________ Date __________________

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Suspension Bridges With spans from 2,000 feet upwards, suspension bridges are the longest bridges built. The problem is that they are also the most expensive to build. Their basic feature is the suspension of the roadway from towers using enormous cables. The cables are not attached to the towers: the towers only transmit the weight to anchorages, which are usually imbedded in huge blocks of concrete or directly in bedrock. The first material used for cables was twisted grass rope, later it was chains, and today it is steel. A single steel wire only 0.1 inch thick can hold over a thousand pounds without breaking. The cables used for the longest bridges may have a diameter of almost four feet! In 1998, the Akashi Kaiyko Bridge in Japan became the longest suspension bridge in the world - with a span of 5973 feet, it surpassed the Humber Bridge in England (longest until then) by over 25%. Other well-known suspension bridges include the Golden Gate in San Francisco, and the Brooklyn Bridge in New York. Wind is a serious concern when building any kind of bridge, but it can be a fatal problem with suspension bridges. The Tacoma Narrows Bridge in Washington actually collapsed in a 40 mile-per-hour wind. Since then, wind tunnel testing is mandatory for all suspension bridge designs. 1. Suspension bridges .............. . a. are not built with very long spans b. are usually inexpensive to build c. always have a roadway suspended from a tower / towers d. never have anchorages 2. The material used for cables today is.... The first material used was .... a. steel, cast iron b. chains, twisted grass c. titanium, copper wire d. steel, twisted grass 3. The longest suspension bridge in the world is ........... . a. located in the USA b. located in Japan c. the Golden Gate d. the Akashi Kaiyko Bridge in England 4. The reason for the collapse of the Tacoma Narrows Bridge was ............. . a. an absence of a wind tunnel test b. a 40 mile-per-hour wind c. a neglected detail in a wind tunnel test

d. a hurricane with 400 mile-per-hour winds

Bridges Name ___________________________________________ Date __________________

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Cable-Stayed Bridges Cable-stayed bridges may get confused with suspension bridges, but there are very important differences. A suspension bridge has towers to transfer the weight of the roadway to anchorages at the ends, but the cables of cable-stayed bridges are attached to the tops of the towers, and there are no anchorages. The towers have to hold the whole weight. The cables can be attached in different ways: either in a parallel or in a radial (or ‘round’) pattern. In a radial pattern, the cables affixed to points along the whole roadway are attached to one point - the top of the tower; in a parallel pattern they are fastened at regular intervals along the whole tower. Cable-stayed bridges were invented more than four hundred years ago, but they were first built in the twentieth century. They were used in Europe after World War II for fixing bombed-out bridges whose pillars remained standing. Today they are becoming increasingly popular for spans of medium length (500 to 2,800 feet), because they are cheaper and faster to build and require less material than suspension bridges. 1. Cable-stayed bridges ............... . a. never have anchorages b. may have one anchorage

c. have towers which transfer the weight of the roadway to an anchorage

d. usually have more anchorages than suspension bridges 2. Bombed-out bridges were rebuilt as cable-stayed bridges .............. .

a. in Europe after World War I b. four hundred years ago c. in the twentieth century d. only in Germany after World War II 3. Which of the following statements is true?

a. Cables attached in a radial pattern are fastened to the piers at several points.

b. In a cable-stayed bridge, cables may only be attached in a parallel pattern.

c. Suspension bridges are more expensive to build than cable-stayed ones.

d. Medium length spans range from 280 to 5,000 feet.

Bridges Name ___________________________________________ Date __________________

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Answer the following questions comparing the different types of bridges: Page 1

1. Which two types of bridges use cables to suspend the roadway from towers? a. arch bridges and suspension bridges b. suspension bridges and beam bridges c. cable-stayed bridges and suspension bridges d. beam bridges and cable-stayed bridges

2. Label the following bridges according their respective types: a. ___________________ Lake Ponchartrain Causeway b. ___________________ Pont du Gard c. ___________________ Brooklyn Bridge d. ___________________ Humber Bridge

3. Which of the following statements is false? a. The Akashi Kaiyko Bridge is longer than the Lake Ponchartrain

Causeway. b. The Golden Gate Bridge is located in San Francisco. c. The Pont du Gard is older than the Akashi Kaiyko Bridge.

d. The Brooklyn Bridge and the Tacoma Narrows Bridge are both suspension bridges.

4. What materials are being commonly used for bridge construction today? a. stones, chains and steel b. steel and concrete c. pre-stressed concrete, steel and twisted grass d. timber, stones and mortar

5. Which is NOT an advantage of a cable-stayed bridge over a suspension one? a. It can have a longer span. b. It is cheaper to build. c. Less material is needed. d. Its construction usually takes less time.

6. Label each span characteristic with the correct bridge a. ___________________ have the longest spans of all bridge types b. ___________________ cannot have a span longer than about 250 feet c. ___________________ usually have medium-length spans d. ___________________ spans are often linked together

7. Which kinds of bridges may have problems with clearance either during construction or when finished?

a. beam bridges and suspension bridges b. suspension bridges and arch bridges c. beam bridges and arch bridges d. cable-stayed bridges and beam bridges

Bridges Name ___________________________________________ Date __________________

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8. If a bridge were to be built in your neighborhood which type of bridge would you prefer? Why? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Label each of the following bridges correctly, and write what clue let you know what type of bridge it is.

9. _____________________________ _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

10. _____________________________ __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

11. _____________________________ _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Bridges Name ___________________________________________ Date __________________

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Answer sheet Arch bridges

1. d 2. c 3. b 4. a Beam bridges

1. b 2. c 3. d 4. c Suspension bridges

1. c 2. d 3. b 4. b Cable-stayed bridges

1. a 2. c 3. c Review

1. c 2. a. beam b. arch c. suspension d. suspension 3. a 4. b 5. a 6. a. suspension b. beam c. cable d. beam 7. c 8. Answers will vary; they should include a personal opinion as well as some

criteria concerning expenses, materials, etc. 9. suspension bridge or cable-stay bridge (the regularly spaced cables coming

down) 10. arch bridge (the arch) 11. beam bridge (the two pillars)