Unit D Lesson D9 Dangerous Forces: When Structures Fail
Completion requirements
Lesson D9: Dangerous Forces: When Structures Fail
Video Lesson
Sometimes, structures collapse due to forces of nature or human mistakes. Watch this video to learn more about some famous structural failures.
Lesson D9: Dangerous Forces: When Structures Fail
Figure D.2.9.1 – Deciduous trees lose their leaves in autumn.
Figure D.2.9.2 – Deciduous trees stand bare in winter.
Breaking Branches
Human-made structures are not the only things that collapse. Natural structures can fail, too, they cannot support the forces acting on them.
Normally, leafy deciduous trees (Figures D.2.9.1 and D.2.9.2) do not collapse in winter. The trunk and branches are able to support the load of snow that falls on the tree.
In September 2014, a snowstorm occurred in Calgary before the leaves had fallen from the trees for the winter. Heavy snow on the surface of the leaves was too much for many trees, and large branches bent and broke.
Click here to read a news article, see pictures, and watch a video of the collapsed trees.
Human-made structures are not the only things that collapse. Natural structures can fail, too, they cannot support the forces acting on them.
Normally, leafy deciduous trees (Figures D.2.9.1 and D.2.9.2) do not collapse in winter. The trunk and branches are able to support the load of snow that falls on the tree.
In September 2014, a snowstorm occurred in Calgary before the leaves had fallen from the trees for the winter. Heavy snow on the surface of the leaves was too much for many trees, and large branches bent and broke.
Click here to read a news article, see pictures, and watch a video of the collapsed trees.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 303–306
Materials:
metal paper clips, sandpaper, two glass jars, water, table salt, spoon.
Figure D.2.9.3 – Thunderstorms create damaging high winds and hail.
Figure D.2.9.4 – This tree could not withstand the forces from thunderstorm winds.
Figure D.2.9.5 – Hail can apply damaging forces. This car has many dents caused by a hailstorm.
Figure D.2.9.6 – Storms can cause expensive damage.
Powerful Alberta Storms
In Alberta, powerful thunderstorms are very common. Every year, millions of dollars of damage occur when extreme winds apply forces to trees, buildings, and vehicles.
Due to their flexibility, trees can naturally can withstand high winds. Usually, they bend instead of breaking. But during some storms, winds are so fast and so strong, they apply forces that the trees cannot withstand. When a tree trunk bends, it experiences both tension and compression. If those forces are too high, the layers of the tree will begin to separate and break apart, leading to total failure.
Human-made structures can also suffer damage due to thunderstorm forces. Many homes and cars have been damaged by hail in Alberta. A fast-moving, large piece of hail exerts a large compressive force on whatever it strikes. That may mean denting a car (Figure D.2.9.5) or breaking windows.
In Alberta, powerful thunderstorms are very common. Every year, millions of dollars of damage occur when extreme winds apply forces to trees, buildings, and vehicles.
Due to their flexibility, trees can naturally can withstand high winds. Usually, they bend instead of breaking. But during some storms, winds are so fast and so strong, they apply forces that the trees cannot withstand. When a tree trunk bends, it experiences both tension and compression. If those forces are too high, the layers of the tree will begin to separate and break apart, leading to total failure.
Human-made structures can also suffer damage due to thunderstorm forces. Many homes and cars have been damaged by hail in Alberta. A fast-moving, large piece of hail exerts a large compressive force on whatever it strikes. That may mean denting a car (Figure D.2.9.5) or breaking windows.
Watch More
Alberta Storms
While you watch these Alberta storms, think about the forces exerted by wind and hail.
Figure D.2.9.7 – Large sections of glaciers fall into the sea.
Figure D.2.9.8 – Most of Greenland is covered with a permanent ice sheet.
Collapsing Glaciers
Enormous chunks of ice are starting to fall from continental ice sheets in Greenland and Antarctica, as you can see in Figure D.2.9.7. Scientists think the cause is an increase in global temperatures. Warmer air makes more cracks form in the ice sheets. Eventually, when the ice cracks get big enough, huge icebergs fall from the ice sheet.
Enormous chunks of ice are starting to fall from continental ice sheets in Greenland and Antarctica, as you can see in Figure D.2.9.7. Scientists think the cause is an increase in global temperatures. Warmer air makes more cracks form in the ice sheets. Eventually, when the ice cracks get big enough, huge icebergs fall from the ice sheet.
Figure D.2.9.9 – Antarctica is an entire continent covered in an ice sheet.
Figure D.2.9.10 – Cracks form in ice sheets when the ice starts to melt.
Watch More
Watch this video to see a massive piece of ice break from an ice sheet in Greenland.
Figure D.2.9.11 – A support tower such as this collapsed at Whistler Blackcomb in 2008.
Figure D.2.9.12 – Without proper design of structures, ice can cause serious structural problems.
Learning from Nature
Storm damage and collapsing glaciers provide excellent lessons for engineers on the importance of knowing how building materials behave in various conditions. Temperature change must be taken into careful account. For example, at Blackcomb Mountain in Whistler, BC, in 2008, a gondola support tower collapsed, sending skiers falling to the ground and injuring 10 people.
Whoever designed the gondola support towers (Figure D.2.9.11) did not take into account water getting inside pipes and tubes of the towers. The water freezing into ice and expanding caused pressure strong enough to snap the steel of the support tower. In this case, the designer should have been aware of the possibility of damage caused by expanding ice, also known as ice-jacking.
Storm damage and collapsing glaciers provide excellent lessons for engineers on the importance of knowing how building materials behave in various conditions. Temperature change must be taken into careful account. For example, at Blackcomb Mountain in Whistler, BC, in 2008, a gondola support tower collapsed, sending skiers falling to the ground and injuring 10 people.
Whoever designed the gondola support towers (Figure D.2.9.11) did not take into account water getting inside pipes and tubes of the towers. The water freezing into ice and expanding caused pressure strong enough to snap the steel of the support tower. In this case, the designer should have been aware of the possibility of damage caused by expanding ice, also known as ice-jacking.
Figure D.2.9.13 – Venice is a beautiful city in Italy.
Figure D.2.9.14 – When the city of Venice floods, people have to walk on narrow platforms above the water.
The Sinking City of Venice
The 1500-year old city of Venice is located on small islands along the coast of mainland Italy. The islands of Venice have sandy soil. Sand moves easily, making it unstable for structural foundations. To solve this problem, Venetians put long wooden posts into the ground with platforms on top. The wood posts and platforms were a stable foundation for Venetian buildings.
Unfortunately, the city of Venice has begun to sink. The pumping of drinking water from the ground under the city has caused some of the sinking. Less water provides less support in the ground to hold up the load of the city.
Adding to the problem in Venice are rising sea levels from global warming. The city sinking and the ocean rising causes Venice to flood regularly.
The 1500-year old city of Venice is located on small islands along the coast of mainland Italy. The islands of Venice have sandy soil. Sand moves easily, making it unstable for structural foundations. To solve this problem, Venetians put long wooden posts into the ground with platforms on top. The wood posts and platforms were a stable foundation for Venetian buildings.
Unfortunately, the city of Venice has begun to sink. The pumping of drinking water from the ground under the city has caused some of the sinking. Less water provides less support in the ground to hold up the load of the city.
Adding to the problem in Venice are rising sea levels from global warming. The city sinking and the ocean rising causes Venice to flood regularly.
Figure D.2.9.15 – Builders in Venice pushed wood logs into the ground to make the city's foundation.
Watch More
Venice Flood Prevention
Watch this video to see Venice when it floods.
Watch this video to see Venice when it floods.
Currently, engineers are constructing structures to prevent Venice from flooding. Watch this video to see how giant flood gates are being built in Venice.
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The Power of Nature
Structures fail for several reasons. Sometimes, extreme forces of nature cause structural failure. Watch this video to see the effects of strong earthquakes on structures:
Structures fail for several reasons. Sometimes, extreme forces of nature cause structural failure. Watch this video to see the effects of strong earthquakes on structures:
For buildings to stay standing in strong winds such as tornadoes is difficult.
In 1987, a tornado ripped through Edmonton and destroyed many houses and buildings. Click here to read an article and watch some videos about the Edmonton tornado.
In 1987, a tornado ripped through Edmonton and destroyed many houses and buildings. Click here to read an article and watch some videos about the Edmonton tornado.
Structural Material Failure
Sometimes structures collapse because the materials within the structure fail. Watch this video to see a 200-year old apartment building in Lisbon, Portugal, collapse suddenly. The building fell because moist sea air weakened the mortar between the bricks.
Sometimes structures collapse because the materials within the structure fail. Watch this video to see a 200-year old apartment building in Lisbon, Portugal, collapse suddenly. The building fell because moist sea air weakened the mortar between the bricks.
Design Errors
Sometimes structures fail because humans make mistakes in the design.
In 2007, a bridge collapsed in Minneapolis, USA. At the time, workers were repairing the bridge deck. An extra 261 000 kilograms of construction materials were sitting on the deck, adding to the load of the bridge.
Investigators determined that pieces of metal connecting the sections of the bridge were too thin to support the extra load on the bridge.
Sometimes structures fail because humans make mistakes in the design.
In 2007, a bridge collapsed in Minneapolis, USA. At the time, workers were repairing the bridge deck. An extra 261 000 kilograms of construction materials were sitting on the deck, adding to the load of the bridge.
Investigators determined that pieces of metal connecting the sections of the bridge were too thin to support the extra load on the bridge.
Watch this video to see the Minneapolis bridge collapse and understand more about what caused this structure to fail.
Connections
Connections: Careers
>> Engineer
Engineers use their knowledge of science and math to design structures. Mechanical engineers design machines. Civil engineers design structures such as bridges, buildings, and roads. Electrical engineers design structures for power grids and other devices that use electricity.
If you ever meet a Canadian engineer, look at his or her hands. Likely, you will see a small ring on one pinky finger. When engineers graduate from a Canadian university, they receive iron rings in a special ceremony.
The iron ring tradition started in 1925 after the Quebec Bridge failed twice. Wearing the iron ring is meant to serve as a reminder to engineers about the seriousness of their jobs and their responsibility to keep other people safe when they design structures.
>> Engineer
Engineers use their knowledge of science and math to design structures. Mechanical engineers design machines. Civil engineers design structures such as bridges, buildings, and roads. Electrical engineers design structures for power grids and other devices that use electricity.
If you ever meet a Canadian engineer, look at his or her hands. Likely, you will see a small ring on one pinky finger. When engineers graduate from a Canadian university, they receive iron rings in a special ceremony.
The iron ring tradition started in 1925 after the Quebec Bridge failed twice. Wearing the iron ring is meant to serve as a reminder to engineers about the seriousness of their jobs and their responsibility to keep other people safe when they design structures.
Figure D.2.9.17 – Canadian engineers wear iron rings.
Figure D.2.9.18 – The Japanese fishing boat Ryou-Un Maru was lost at sea in 2012 without a crew. This is how it looked one year later when discovered off the coast of Haida Gwaii, BC.
Figure D.2.9.19 – Rust changes the colour and strength of iron.
Corrosion and Structural Failure
Corrosion occurs when a material wears away or weakens slowly over time. A common form of corrosion is rusting. Rust forms when iron is exposed to oxygen and water. Rust is usually red-coloured, but sometimes it can be green-coloured.
Corrosion is a common cause of failure of structures. Steel, which contains iron, is used to build towers, cars, and ships.
Rust is a flaky substance, which means it can cause holes or cracks in iron objects. These weak points in the structure can cause the remainder of the structure eventually to fail.
In 1983, the Mianus River Bridge in Connecticut, USA, collapsed from rust formation. Click here to watch a news report about this bridge failure.
Corrosion occurs when a material wears away or weakens slowly over time. A common form of corrosion is rusting. Rust forms when iron is exposed to oxygen and water. Rust is usually red-coloured, but sometimes it can be green-coloured.
Corrosion is a common cause of failure of structures. Steel, which contains iron, is used to build towers, cars, and ships.
Rust is a flaky substance, which means it can cause holes or cracks in iron objects. These weak points in the structure can cause the remainder of the structure eventually to fail.
In 1983, the Mianus River Bridge in Connecticut, USA, collapsed from rust formation. Click here to watch a news report about this bridge failure.
Watch More
In 2012, a parking lot roof collapsed in a shopping mall in Elliot Lake, Ontario. Steel beams supporting the roof were badly rusted. The beams were not properly waterproofed, and road salt from cars added to the problem. Watch this news report about the
Elliot Lake mall collapse.
Try It!
Paper Clip Corrosion
Try this simple experiment at home to corrode a few paper clips. Obvious changes might require a few days after you begin the experiment.
Materials:
Try this simple experiment at home to corrode a few paper clips. Obvious changes might require a few days after you begin the experiment.
Materials:
- three metal paper clips
- piece of sandpaper
- two glass jars
- water
- spoon
- table salt
Instructions:
- With the sandpaper, lightly sand the protective coating from the surface of all the paper clips.
- Fill two glass jars half full with water. Label one jar Tap Water.
- To the other jar, add 4 spoons of table salt and stir. Label this jar Salt Water.
- Put one sanded paper clip into each jar, and leave the third paper clip sitting in the air.
- Observe the jars daily for a week. What do you notice?
Questions:
Think about the following questions very carefully; then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully; then, type or write your answers. After you have your answers, click the questions for feedback.
The paper clip in salt water rusted most quickly.
The paper clip in air rusted most slowly.
If a ship is not painted, the iron in the steel ship is exposed to salt water in the ocean. Salt water makes iron rust more quickly. Rust on a ship could produce holes in the ship and cause the ship to sink.
Figure D.2.9.20 – Rust can lead to holes and weaknesses in a structure.
Figure D.2.9.21 – Nails are galvanized to prevent rusting.
Why Do We Use Iron?
If iron rusts so easily, why do we use it?
Iron is strong, which is why it is used in so many structures such as bridges, buildings, ships, and vehicles. Also, iron is one of the most common metals on Earth, which means it relatively inexpensive to use.
Corrosion of iron can be prevented in several ways. Covering the iron with paint prevents contact with air and water. If car paint is scratched, the iron beneath is exposed to air and can begin to rust, which forms holes in the cars structure.
Iron can be coated with other metals to prevent exposure to air and water. This is called plating. Galvanized iron has been coated with zinc, a metal that does not corrode so easily. Chrome plating on cars is iron that has been plated with chromium.
If iron rusts so easily, why do we use it?
Iron is strong, which is why it is used in so many structures such as bridges, buildings, ships, and vehicles. Also, iron is one of the most common metals on Earth, which means it relatively inexpensive to use.
Corrosion of iron can be prevented in several ways. Covering the iron with paint prevents contact with air and water. If car paint is scratched, the iron beneath is exposed to air and can begin to rust, which forms holes in the cars structure.
Iron can be coated with other metals to prevent exposure to air and water. This is called plating. Galvanized iron has been coated with zinc, a metal that does not corrode so easily. Chrome plating on cars is iron that has been plated with chromium.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to
guide your learning.
Unit D Lesson 9 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
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Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Winters in Ontario and Quebec are warmer and salt is used to melt ice on their roads more often than it is in the Prairies. When road salt comes into contact with cars, any exposed iron parts on the car rust faster than painted surfaces do.
Salt is used in the winter to melt ice on roads. Salt speeds the process of rusting. Washing your car in the winter removes road salt from the car to prevent corrosion.
Tornadoes and earthquakes are two natural causes of structural failure. In tornadoes, the shear force from extremely strong winds causes walls of buildings to be pushed over. In earthquakes, the shear force from the ground moving in opposite
directions causes buildings to be moved on their foundations and fall.
An engineer uses his or her knowledge of math and science to design structures that humans can use safely.
Much snow falls in the mountains. The load of snow on the house could cause structural stress and fatigue on the structure.