Weekly Online Lesson Online Lesson Archive Grade Level: 8-12 Subject: Engineering

Bridge Collapse

A 600-foot section of an interstate bridge over the Arkansas River collapsed Sunday, May 26, when one of two barges going north on the river rammed a pylon. About a dozen vehicles plunged into the river. Five people were rescued from the water, but authorities are certain that there were fatalities.

The accident knocked out four spans of the 1,988-foot bridge. Structural damage was so severe that it ripped apart the concrete seams at the river's banks. The bridge collapsed on top of the barge, which remained in the river.

I-40 is the major east-west route through Oklahoma, with an estimated 20,000 vehicles crossing the bridge daily. The bridge is about 100 miles east of Oklahoma City, 40 miles from the border with Arkansas. Some authorities estimate the bridge will take a year to fix, while others hope it will reopen within six months.

Not overlooking the tragedy of this accident, this week's online lesson focuses on the design and construction of bridges.

Bridge Basics

For all their shapes and variety, there are really only four main types of bridges. Go to Building Big: Bridge Basics at PBS and learn about these four types: beam, truss, arch, and suspension. As you read, click the underlined words for definitions. After learning about each bridge type, visit the links that follow. You can learn about the forces that act on that type of bridge or learn about related bridge types. Give an example of each type of bridge. From the photos of the I-40 bridge above, what type of bridge would you say it is?

While at the PBS site, take a look at the Wonders of the World databank, where you can choose from a list of 13 bridges (and other structures) that are considered engineering wonders. Read them all, but look for at least one example of each type of bridge. Which is the longest of each type of bridge? Which is the longest of all the bridges listed? Which is the oldest?

Before you go, the community of Craggy Rock needs your help. Click the Bridge Challenge link and select the right type of bridge for each location. Click each number on the town map to learn the requirements for each location, and then choose the right bridge. Keep going until you have just the right bridge plan for all four locations.

Bridges of Allegheny County

There are a lot of bridges in Allegheny County, Pennsylvania — so many, in fact, that visitors can take one of several bridge tours. Go to pbhbridges.com to learn more about the local bridges. Soon you can take a virtual tour yourself, but first visit the Bridge Basics page. Some of this information you already learned, but the page does a nice job of "building" upon the four basics types of bridges. You'll be surprised at all the variations.

What are the four main factors used in describing a bridge? Deck, pony, and through are words used to describe what? What does a hinge do? What is the advantage of a king post over a queen post? Who was the first American to use mathematical calculations in truss design? What problem did E. M. Wichert solve in 1930?

Now that you're a bridge expert, take a tour. Choose a river or town, and then click begin tour. Using the menu in the frame above, click the name of any bridge (black ones are still standing). You'll probably find that the earlier ones look more interesting. See if you can name each bridge type from the photograph.

Bridge Design Tips

Many high schools sponsor model bridge building competitions. If designed and constructed correctly, ridges made of toothpicks, popsicle sticks, balsa wood, or even spaghetti can support a surprising amount of weight. If you are planning on participating in a competition like this, visit ABCD's Bridge Design Tips for Kids. Here you will find plenty of good advice, regardless of the bridge "constraints" you are faced with.

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