BRIDGES Bridges have changed the quality of life for people.

Form What is a bridge? A bridge is a structure created (by nature or by humans) to span a physical obstacle like a river, stream, valley or road. The design of a bridge depends on the obstacle, the terrain, the materials available, funds available, and the situation.

Causation What was the problem that caused a need for the first bridge? People needed to get themselves and their stuff from one place to another. Sometimes that path was difficult because of rivers, streams, and deep caverns. The first bridges were probably made of wooden logs and stones.

Function How do bridges work? What are the various kinds of bridges? All bridges span an obstacle. Bridges are classified based on how forces are distributed throughout the structure. On the next few slides you can see names and pictures of different kinds of bridges.

Beam bridges have beams that are supported on either end. A beam can be metal or wood. This bridge’s beam is a tree log.

Truss bridges support weight with criss-crossing metal that form strong triangles. These are trusses. The triangles of metal give the bridge strength.

Arch bridges have an arch or series of arches that send the weight of the bridge to the bridge’s abutment. The bridge’s abutment – the place where two arches converge and find support.

Suspension bridges are bridges that are suspended from cables. These are the cables that support the bridge. Suspension bridges can span very long obstacles.

Connection What impact do bridges have on the quality of our lives? We can now move from one place to another without going around obstacles. We can transport objects across obstacles. Bridges allow us to save travel time and travel safely from one place to another regardless of dangerous obstacles.

Connection What are the trade-offs? Bridges need lots of materials – cement, stone, wood, metal, etc. Bridges are very expensive to design and build – lots of materials and lots of people. They need very knowledgeable architects and engineers to design safe bridges. Bridges cost a lot of money to maintain so that they do not fail. Some bridges disturb sensitive environments, like the proposed bridge in Stillwater, MN.

Connection What are the risks? If they are not properly maintained, bridges will eventually fail. Maintenance is very expensive! Building bridges is dangerous work for construction workers. Their structure is fragile and can be damaged easily by boats, barges, earthquakes, and storms.

Change How have bridges changed over time? This is the “Arkadiko” bridge in Greece. It is one of the world’s oldest arch bridges. It’s from about 13 BC. That’s 2025 years old!

Change How have bridges changed over time? This is yet another arch bridge from around the 1 st century BC. It can be found in Spain and was built by the Romans.

Change How have bridges changed over time? This is a bridge in Italy from about the 1 st or 2 nd century. It’s an arch bridge that was built to carry water from lakes and rivers to the densely populated cities of Italy. It’s called “the aqueduct.”

Change How have bridges changed over time? This model is of a buiding design that included a bridge to connect the two buildings – kind of like a “sky way.” The model was built in China sometime between 200 BC and 200 AD.

Change How have bridges changed over time? This bridge can be found in Iran and spans the Zayandeh Rud River. It was built between That means that it took over 200 years to build!

Change How have bridges changed over time? This is one of the most famous bridges in the US. It is in New York and connects Mahattan and Brooklyn. It’s named The Brooklyn Bridge and was built in 1883.

Change How have bridges changed over time? Yup, you’re seeing things correctly. This is a water bridge in Europe. Sometimes, even boats need to be able to cross obstacles. This is a beam bridge filled with water. You can walk or boat across it.

Change How have bridges changed over time? This is the world’s longest bridge. It’s 22 miles long and spans a section of ocean in China. It cut driving time between two major cities from 4 hours to 2.5 hours. It’s part beam bridge and part suspension bridge.

Change How have bridges changed over time? As you can see, bridges have always been quite spectacular, complicated, and innovative. That being said, our available technology makes it much more possible to span long distances, enormously deep caverns, rough terrain, and solve problems in travel once thought impossible to solve. I wonder what bridge engineers will think of next?!

Reflection What have we learned from bridge failures One of the most famous bridge collapses was the Tacoma Narrows Bridge, which at the time was the third longest suspension bridge in the world and spanned the Puget Sound in Washington. It opened and collapsed in the same year, 1940, and has influenced and changed the engineering of suspension bridges ever since. Click on the link above to watch the bridge collapse!Tacoma Narrows Bridge

Responsibility Who is responsible and what is their responsibility? The civil engineers who design bridges need to understand physics and other scientific principles to design sturdy and safe bridges. They also need to understand materials, weather, terrain, cost, and the environment. They need to consider the amount of weight the bridge needs to support and the amount of traffic it’ll carry. They also need to have excellent math ability to calculate distance and weight and must be able to keep up with new ideas, learn from past failures, keep up with computer design technology, and employ competent people to actually build their design. The civil engineer is ultimately responsible for a bridge’s success or failure!

For more information… /bridge.htm /bridge.htm