Week 26 - Safe Structures, Strengthening Materials and Evaluating Designs

Exercise 4.1


Lesson 4.1: Building Safe Structures in All Environments


ACTIVITY A: Margins of Safety



Required Readings

Science in Action 7
pages 324 to 328
or

Science Focus 7

pages none


Technology uses scientific knowledge and principles to build practical products. As scientific enquiry uncovers new information about material construction, technologists incorporate that knowledge into new designs and new materials. Above all, the structures that are built must be safe to use. In this lesson we will examine how safety margins are built into the structures we use.

Now that you have read the assignment in the text, define the term 'Margin of Safety' and give and example of how the term is used in the exercise below.

The safety margin for sports equipment is set very high as well. Bicycle helmets must be able to protect the rider's head even when the bike is operated a fairly high speeds. Some old time riders don't feel there is a need for a helmet when riding a bike. But if I asked you to run headlong into a brick wall at your fastest running speed you would think I was crazy! But you and I often travel faster than we can run on our bikes. Do you wear a helmet?

Helmets are an important piece of safety equipment that protects your head if you fall off your bike or are involved in an accident. Helmets must adhere to strict standards and be certified by a national council. To be certified, each helmet design must be thoroughly tested to ensure it stands up to various types of impact. If the helmet fails a certain type of test, it will not be certified and available for purchase. Consumers trust that they are buying a piece of safety equipment that will protect them, so this certification process could be a matter of life and death! This video demonstrates how motorcycle helmets are tested.

In order to build in safety margins you must know the environment it will be operating in. Should the safety margins be the same for race cars and your family car? If they were your family car would be fairly bare and uncomfortable, because you would have to wear a special seat belt, helmet. Your car wouldn't go very far either as the gas tanks in race cars are very small. How about building standards for homes built in Florida and Edmonton? This next section will examine some structural differences in homes from these two environmentally different areas.



ACTIVITY B: Varying Environmental Conditions Determine Structural Safety Standards

Roofs in Alberta's Rocky Mountains need to be designed to carry heavy snow loads.

In Florida, each year hurricane winds destroy many homes and businesses. Usually, the roof is torn off the house first.



The environmental factors that determine the safety standards for homes are quite different when we compare the state of Florida and the province of Alberta. Hurricanes that can rip the roofs off homes are not uncommon in Florida but never happen in Alberta. Heavy snow loads can build up on and crush roofs of Alberta homes, but is not likely to happen in Florida.

How do you think the design of the roof structure might be different in an Alberta home when compared to one found in Florida? Roofs of Alberta homes have strong supporting materials while the roofs of Florida homes are tied to the house by metal fasteners to keep the wind from blowing the roof off.

Each state and province has building codes so that buildings are built with margins of safety for the climatic conditions that are found there.

EARTHQUAKES

During earthquakes some building remain standing while others fall. Why?



The west coast of North America has very active geological activity. Earthquakes are quite common. The building codes for British Columbia and all the western states must account for earthquakes so that an adequate margin of safety is maintained. But how big of an earthquake should they with stand. What about freeway overpasses or bridges?

This overpass collapsed because the pillars were not designed to be earthquake proof.


Exercise 4.1: Disaster Proof Housing