D. Structures and Mechanisms · Strong and Stable Structures

Why Strong and Stable Structures Matter

D1.1 A3.1 A1.5About 35 minutes

Learning goals

I can explain how strong and stable structures help people and communities.
I can describe what can happen when structures are not strong or stable enough.
I can describe effects of building structures on the environment.
I can weigh the good and bad effects of a structure and give my opinion with reasons.

Words to know

society
All the people who live together in a community, a town or a country.

community
A group of people who live, work and play in the same area.

building code
A set of rules builders must follow so structures are safe, strong and stable.

accessible
Easy for everyone to reach and use, including people who use wheelchairs, walkers or strollers.

assess
To judge something by thinking about its good and bad effects.

Imagine a town with no strong structures

No bridges to cross the river. Roofs that cave in after a snowstorm. An arena that is not safe to skate in. A town like that would not work very well!

Strong and stable structures let us live safely, travel, learn, work and play. But building them also affects the environment. Today you will assess both sides.

How strong and stable structures help society

Shelter and safety: strong roofs hold heavy snow, and stable houses stand up to wind, keeping families safe and warm.
Travel and connection: bridges join communities. The Confederation Bridge, about 13 km long, connects Prince Edward Island to New Brunswick, so people can drive across instead of taking a ferry.
Services: hospitals, schools, fire stations and water towers must be strong so they keep working, even in storms.
Getting around for everyone: strong ramps, railings and elevators make buildings accessible for people who use wheelchairs, walkers or strollers.
Fun and community: arenas, playgrounds, community centres and bleachers hold big crowds safely.

A long concrete bridge with many supports crosses a wide river to a town with houses and a church. — Bridges join communities. Strong supports let cars cross the river safely every day. AI-generated image

When structures fail

When structures are not strong or stable enough, people can be hurt and communities can be cut off.

In January 1998, a huge ice storm hit eastern Ontario, Quebec and nearby places. Thick ice built up on power lines and towers. The extra load was so heavy that many towers collapsed, and many people lost power for days or even weeks in the cold.
After very heavy snowfalls, some roofs have sagged or caved in under the load.

Because of problems like these, Canada has building codes: rules that say how strong and stable structures must be. Engineers check plans, and inspectors check buildings.

Effects on the environment

Building any structure uses resources from nature: trees for wood, rock and sand for concrete, metal from mines, and energy to make and move it all. It can also take away habitats.

But strong, long-lasting structures can be better for the environment than weak ones. If a structure lasts 100 years instead of 10, people do not need to tear it down and rebuild it many times, so there is less waste and fewer resources are used.

Over 100 years, one strong building uses far fewer materials than a weak one that must be rebuilt again and again.

Structure	Helps society by...	Possible effects on the environment
a bridge over a river	connecting communities; shorter trips	building it disturbs the riverbank; shorter trips can mean less fuel used
a strong, well-built house	keeping a family safe and warm for many years	uses wood and other materials; lasting a long time means less waste
an arena	a place for hockey, skating and events	uses land and lots of energy to keep the ice frozen
a ramp at a library	lets everyone get inside	very small: uses a little concrete or wood

Assessing some structures

Worked example

Let's assess a structure

Your community wants to build a new footbridge across a creek so kids can walk to school instead of being driven the long way around. Assess it.

Helps society: kids can walk safely to school; families save time; it is good exercise.
Must be strong and stable: it must hold many children at once (live load), plus snow, and stay steady in floods and wind.
Environment, harmful: building it disturbs plants and soil along the creek for a while; it uses materials like wood or steel.
Environment, helpful: fewer car trips means less fuel burned and less air pollution.
Opinion with reasons: I think the bridge is a good idea if builders protect the creek banks while they work.

The footbridge has more good effects than bad, as long as it is built strong and stable and the creek is protected.

Assessing means weighing the good effects against the harmful ones. For the footbridge, the helpful side is heavier.

Worked example

Let's think about a failure

A backyard deck was built with too few supports. When 12 people stood on it at a party, it sagged and cracked. What went wrong and what could have prevented it?

The 12 people were a big live load.
With too few supports (columns), each support had to hold too much, so the deck was not strong enough.
To prevent it: follow the building code, add more supports, use bigger beams, and add braces.
Effect on society: people could have been hurt, and the deck must be rebuilt, which costs money and uses more materials.

The deck was not strong enough for its live load. Following building rules and adding supports would have prevented it.

Just for fun

Why does the footbridge get invited to every party?

Because it is so good at bringing people together!

Hands-on activity

Community structure report

You need: paper, a pencil, and a walk around your neighbourhood with a grown-up.

Choose one structure in your community: a bridge, a school, an arena, a water tower, a playground, a library ramp, a bus shelter.
Answer:

What is its function? Who uses it?
How does it help people (society)?
What makes it strong? What makes it stable? (Look for triangles, columns, wide bases, foundations, braces.)
What effects might it have on the environment, helpful and harmful?

Give your opinion: Is this structure good for your community? Give two reasons.
Share your report with your family, like a reporter on the news.

What to look for: clear reasons for each answer, at least one helpful and one harmful effect, and an opinion supported by reasons. Safety: stay with your grown-up near roads and do not climb on structures.

Your turn

Name two ways strong and stable structures help people.

What is a building code?

What happened to many power towers in the 1998 ice storm?

Name one way building a structure affects the environment.

Why can a long-lasting structure be better for the environment?

What does accessible mean?

More practice: warm-up

Which structure connects Prince Edward Island to New Brunswick?

Does a ramp make a building more accessible or less accessible?

Is a hospital a structure that must be very strong? Why?

What does assess mean?

Name one resource used to build structures.

More practice: on your own

Why must a school roof in Ontario be strong enough to hold heavy snow?

A new arena is being built. Give one good effect for society and one effect on the environment.

Why do inspectors check new buildings?

How can a bridge help the environment?

Give an opinion with a reason: should your town build a skate park in an empty lot?

Challenge

A company can build a bus shelter cheaply with thin, weak materials that will last 5 years, or with stronger materials that cost more but last 30 years. Which is better for the environment? Explain.

Why might it be important for a fire station to be stronger and more stable than a garden shed?

Name a structure that is good for society but has a harmful effect on the environment. Suggest a way to reduce the harm.

Check your understanding

Quiz

Strong and stable structures help society by...

A building code is...

In the 1998 ice storm, many power towers collapsed because...

Which is an effect of building on the environment?

Why can a long-lasting structure be better for the environment?

A ramp at a library makes the library more...

For parents and teachers

Big idea: Students assess the effects of strong and stable structures on society and the environment (D1.1). Strong, stable structures give shelter, safety, travel, services and accessibility; failures (like the towers that collapsed in the 1998 ice storm) show why building codes matter. Building uses resources and can take habitats, but long-lasting structures reduce waste. The community structure report connects science to real places (A3.1) and practises giving an opinion with reasons (A1.5).

How to help: When you pass bridges, arenas, ramps or construction sites, ask: "Who does this help? What did it take to build? What might it change for plants and animals?" Encourage "I think... because..." answers.

Common difficulties:

Giving an opinion with no reasons. Ask, "What makes you think so?"
Thinking the cheapest choice is always best. Talk about how long things last and how often they must be replaced.

A note on the ice storm: if your child finds the idea of collapsing structures worrying, reassure them that building rules and engineers' checks keep most structures safe, and that we learn from storms to build even better.