What Bridge Is This? The Tower Bridge (London, England, United Kingdom) is a draw bridge suspension bridge combination that was completed in 1894.
Bridges over time have been made from many different materials. What a bridge is made from can make a difference on how strong the bridge is, and how durable a bridge is (or how long that bridge will last without breaking).
The picture below shows a simple comparison between four popular materials used for bridge making: rope, stone, wood, and steel. The picture compares each of the material's strength versus their cost.
Before you go further, make sure you read "Science of Bridges" and understand how forces affect bridges.
The way people have built bridges has changed imensely over time. This includes what the bridges are made of. "This gradual evolution—and extension—of bridges has been made possible partly by a deeper understanding of engineering, but also by the development of far stronger materials" (Woodford, 2016).
Early Bridges: Rope and Wood
Before the middle ages, (around 1100 A.D), basic materials such as rope and wood were used to create bridges. These simple materials helped people cross small creeks, rivers and other small bodies of water. Rope is not used for public bridges anymore. Some wood bridges can still be found, but modern bridges with the purpose of heavy transportation are not made of wood anymore.
Pros: These materials were readily available for people to use, and cost very little to make.
Cons: Neither type of material is very strong. Rope wouldn't be suitable for vehicles to drive across. Wood decays over time due to environmental factors.
Stone
Stone was used alot in the stone age, since about 1100 AD (Jamal 2016). Stone was great for building arch bridges (see "Types of Bridges" ). Stone bridges are still built now, but over small distances with the main purpose of looking nice.
Pros: Beautiful, pleasing to the eye. Can span up to 150 meters. Long lasting and need almost no maintenance.
Cons: Very expensive. Can't safely span across distances much longer than 150 meters.
Concrete
Used in modern bridge making.
Pros: Strong against environmental attacks due to its high compressive strength. The cheapest of bridge materials. Heavier than steel, so it's good for short bridges. Can be formed in a variety of different shapes.
Cons: Tensile strength is weak (See "Science of Bridges" for information on tensile and compressive forces.
Steel
Used in modern bridge making.
Pros: Best for the longest bridges, because it is much lighter than concrete. Its compressive strength is about 10 times as strong as concrete, and its tensile strength is aouut 100 times as strong as concrete's (Jamal, 2016).
Cons: Much more expensive than concrete.
Reinforced Concrete
Often times modern bridges are made from a combination of steel and concrete, which is called reinforced concrete. Reinforced concrete is made by pouring concrete over steel bars.
Pros: This combines the high tensile strength (resistance to pulling forces) of steel with the high compressive strength (resistance to pushing forces) of concrete.
Cons: Timely and costly to make. Also very heavy.
Early Bridges: Rope and Wood
Before the middle ages, (around 1100 A.D), basic materials such as rope and wood were used to create bridges. These simple materials helped people cross small creeks, rivers and other small bodies of water. Rope is not used for public bridges anymore. Some wood bridges can still be found, but modern bridges with the purpose of heavy transportation are not made of wood anymore.
Pros: These materials were readily available for people to use, and cost very little to make.
Cons: Neither type of material is very strong. Rope wouldn't be suitable for vehicles to drive across. Wood decays over time due to environmental factors.
Stone
Stone was used alot in the stone age, since about 1100 AD (Jamal 2016). Stone was great for building arch bridges (see "Types of Bridges" ). Stone bridges are still built now, but over small distances with the main purpose of looking nice.
Pros: Beautiful, pleasing to the eye. Can span up to 150 meters. Long lasting and need almost no maintenance.
Cons: Very expensive. Can't safely span across distances much longer than 150 meters.
Concrete
Used in modern bridge making.
Pros: Strong against environmental attacks due to its high compressive strength. The cheapest of bridge materials. Heavier than steel, so it's good for short bridges. Can be formed in a variety of different shapes.
Cons: Tensile strength is weak (See "Science of Bridges" for information on tensile and compressive forces.
Steel
Used in modern bridge making.
Pros: Best for the longest bridges, because it is much lighter than concrete. Its compressive strength is about 10 times as strong as concrete, and its tensile strength is aouut 100 times as strong as concrete's (Jamal, 2016).
Cons: Much more expensive than concrete.
Reinforced Concrete
Often times modern bridges are made from a combination of steel and concrete, which is called reinforced concrete. Reinforced concrete is made by pouring concrete over steel bars.
Pros: This combines the high tensile strength (resistance to pulling forces) of steel with the high compressive strength (resistance to pushing forces) of concrete.
Cons: Timely and costly to make. Also very heavy.
Which Material Should You Choose?
Civil and structural engineers must decide between what type of material to use when building a bridge. They must weigh their options carefully. They need to find the perfect balance between cost and design, all while making sure the bridge will be safe enough for public use.
Try This at Home! Marshmallow Challenge
Follow this link to complete a team challenge to build the tallest structure out of only twine, spaghetti and tape. This will illustrate the importance of using different materials in building everything from bridges to buildings. This activity can be altered so that each piece of material costs a certain amount and the teams would need to keep track of how much their structure costs.
Click here to participate in the Marshmallow Challenge!
Follow this link to complete a team challenge to build the tallest structure out of only twine, spaghetti and tape. This will illustrate the importance of using different materials in building everything from bridges to buildings. This activity can be altered so that each piece of material costs a certain amount and the teams would need to keep track of how much their structure costs.
Click here to participate in the Marshmallow Challenge!