THE CASE OF TACOMA
NARROWS BRIDGE
Technologies 1º ESO – Structures
Analyzing structures
INTRODUCTION: TACOMA NARROWS BRIDGE
You are going to watch a video about a bridge over Tacoma Narrows. After that, answer the
following questions:
1. How long was the bridge in use before collapsing? 4 months and 7 days
2. What happened to the car on the bridge? It falls in the collapse
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
Analyzing structures
STRUCTURES REQUIREMENTS
The main requirements for a structure to work properly are the following:
• Safety: The structures must warrantee people’s 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.
• Aesthetic appearance: it must have a nice appearance.
• Environment: the design should consider its environmental impact and minimize it.
3
THE TACOMA NARROWS BRIDGE COLLAPSE
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 10:30am, 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.
Analyzing structures
ACTIVITY (Individually in your notebook or in word) What are the requirements that the bridge did not fulfill?
• Safety: Not fullfilled
• Strength: fullfilled
• Stability: Not fullfilled
• Rigidity: fullfilled
• Resistance: Not fullfilled
• Durability: fullfilled
• Economy: fullfilled
• Aesthetic appearance: Not fullfilled
• Environment: fullfilled
