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STRUCTURES

Technologies1st year ESO

(Adapted from a presentation by Manuel Suarez Alvite)

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STRUCTURES

You are going to watch a video about a bridge over Tacoma Narrows. After that you

are going to work for five minutes in groups. Write down the answers and after that

the head of the group will read them.

1.- How long was the bridge in use before collapsing?

2.- What happened to the car on the bridge?

3.- After the collapse of the bridge, what did the authorities do to solve the

problem of crossing the Tacoma Narrows?

http://www.youtube.com/watch?v=3mclp9QmCGs

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STRUCTURES

How can we define a structure?

A structure is an arrangement of designed components that provides

strength to a built device such as a building, bridge, dam, car or airplane.

There are also natural structures although we will focus on manufactured

structures.A structure must

•be capable of carrying the load it was designed for without failing, and•support the load or object in the correct position.

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STRUCTURE REQUIREMENTSThe main requirements for a structure to work properly are the following:

• Safety

• Strength: The structure is designed to be strong enough to support loads due to

its own weight, human activity, and the environment (such as wind, snow,

earthquakes, ice, or floods). The structure will have strength if it has:

• Stability: it must be in the right place and not fall.

• Rigidity: it must not be deformed when in use.

• Resistance: it must support all the efforts and forces applied to it.

• Durability: The materials and details of construction must last. That means that

the structure will not corrode, deteriorate, or break under the effects of

weathering and normal usage during its lifetime.

• Economy: it must not exceed the budget.

• Aesthetics

The Tacoma Narrows Bridge was a bridge built in the state of Washington, across the Tacoma Narrows in 1940. At that time, it was a suspension bridge with a revolutionary design, but four months after opening, a storm caused it to collapse.

Throughout the early morning of November 7th, the central span started to undulate in winds of 55 to 75 km per hour. At about 10:30 A.M., the central span floor panel dropped into the water 59 meters below, and the remainder of the bridge kept twisting. At 11:09 A.M., the remaining sections fell down into the water. The bridge was not strong enough to support the oscillation caused by the windstorm.

The collapse of Tacoma Narrows Bridge did not result in any casualties. The bridge was blocked a few days before it collapsed. However, this design failure brought many engineers worldwide to the realization that they did not have enough understanding of building a suspension bridge.

After the collapse, the engineers started to investigate ways to aid the strength of a suspension bridge. The official investigation into the collapse recommended the use of wind-tunnel tests to aid in the design of the second Tacoma Narrows Bridge. Also, new mathematical theories arose from these studies.

The insurance agent who had written an $800,000 policy on the bridge for the state was so confident of the bridge’s integrity that he pocketed the $70,000 premium instead of forwarding it to the insurance company. He went to jail for two years. Other insurance policies covered most of the bridge’s cost.

THE TACOMA NARROWS BRIDGE COLLAPSE

STRUCTURES: Activity

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What are the requirements that the Tacoma bridge did not fulfill?

What are the requirements that the Leaning Tower of Pisa does not fulfill?