SF.4.a.b Evaluating structures for performance and safety

Which of the following environmental disasters are not due to climate?

• Earthquakes

• Wildfires

• Flooding

• Erosion

All structures are created to satisfy human needs. These needs may vary widely, but the one common to all structures is safety. Environmental factors that affect safety are...(select all that apply).

• Recyclable materials

• Earthquake risks

• Climate & flood risks

• Erosion & terrain

Answer explanation

Recyclable materials refers to sustainability.

Terrain is an important environmental factor to account for when building structures because...(select all that apply)

• When you build on a cliff you can get a great view from your house.

• Unstable soils and steep terrain make building stable structures difficult or unsafe.

• Building on permafrost is unsafe

• Due to climate change, permafrost melt is going deeper in the summertime, making soils unstable for structures.

Margin of Safety refers to...

• how many times a normal load a structure can withstand

• making a structure stronger than it needs to be for aesthetics

• making a structure weaker than it needs to be to save money

• Using margarine instead of butter

Answer explanation

If a structure has a factor of safety of 4, and its function is to hold a 1000N load, at what load will the structure fail?

• 4 N

• 0.25 N

• 4000 N

• 250 N

Answer explanation

The factor of safety is...

• advertised to users, to show users how safe the product is.

• advertised to users, to show users how good value the product is.

• not advertised to users, because it is a trade secret for companies.

• not advertised to users, because users might push the product over the normal range of operation.

Answer explanation

If a bridge is designed to plastically deform at 18,000lbs and the factor of safety is 6, what is the normal operating load of the bridge?

• 3,000 lbs

• 108,000 lbs

• 6,000 lbs

• I don't know.

Answer explanation

Plastic deformation is bad for a bridge! Plastic deformation means it has changed shape and won't go back. In other words, the bridge will fail at 18,000lbs. A factor of safety of 6 means the bridge is designed to hold 6 times the normal load, so we divide 18,000 by 6 to get 3,000lbs for the normal operating load.

A reason to make a structure with a low margin of safety would be...(select all that apply)

• To save money

• To save material

• To save time constructing

• To make the structure less safe

Automobile crash tests are an example of...

• Non-destructive testing

• Destructive testing

• Structural monitoring

• End-user surveying

A building contractor places sensors on bridges to check that thermal expansion strains are within normal limits. This is an example of...

• Non-destructive testing

• Destructive testing

• Structural monitoring

• End-user surveying