Engineering: Civil and Structural (Middle School)
Designing safe structures that support loads
Engineering: Civil and Structural (Middle School)
Designing safe structures that support loads
Engineering - Grade 6-8
- 1
A small pedestrian bridge must support its own weight, people walking across it, and occasional strong winds. Identify each of these as a dead load, live load, or environmental load.
Dead loads are permanent, live loads can move or change, and environmental loads come from nature.
The bridge's own weight is a dead load because it is always there. The people walking across it are a live load because they change over time. The wind is an environmental load because it comes from conditions in the environment. - 2
A beam rests on two supports and holds a 60-newton load in the middle. If the load is shared equally by the two supports, how much upward force does each support provide?
Each support provides 30 newtons of upward force because 60 newtons divided equally between 2 supports is 30 newtons per support. - 3
Explain why triangles are often used in bridge trusses and roof frames.
Think about how easily a square frame can become a diamond shape if it has no diagonal brace.
Triangles are often used because a triangle is a rigid shape that does not easily change shape when forces push or pull on it. This helps trusses and roof frames stay strong and stable. - 4
A student builds two towers from the same number of craft sticks. Tower A has a wide base, and Tower B has a narrow base. Which tower is likely to be more stable, and why?
Tower A is likely to be more stable because a wide base makes it harder for the tower to tip over. The center of mass can move farther before it passes outside the base. - 5
A concrete sidewalk expands slightly on a hot day. Engineers often place small gaps between sidewalk sections. What problem do these expansion joints help prevent?
Most materials change size a little when their temperature changes.
Expansion joints help prevent cracking or buckling. They give the concrete room to expand when it gets warm and contract when it cools. - 6
A bridge deck is 24 meters long. Engineers plan to place support posts every 6 meters, including at both ends. How many support posts are needed?
Five support posts are needed. The posts are at 0 meters, 6 meters, 12 meters, 18 meters, and 24 meters. - 7
Name one advantage and one disadvantage of using steel instead of wood for a large bridge.
Consider strength, cost, weight, durability, and maintenance.
One advantage of steel is that it is very strong and can support heavy loads over long spans. One disadvantage is that steel can be expensive and may rust if it is not protected. - 8
A rectangular frame is wobbly until a diagonal brace is added from one corner to the opposite corner. Explain how the diagonal brace improves the frame.
The diagonal brace divides the rectangle into triangles. This makes the frame more rigid and helps it resist changing shape when forces act on it. - 9
During a site investigation, engineers find soft, wet soil where a building is planned. Why is this a concern for the foundation?
A foundation must transfer the building's load safely into the ground.
Soft, wet soil is a concern because it may compress, shift, or settle under the weight of the building. A weak foundation can cause cracks, tilting, or uneven floors. - 10
A model bridge can safely hold 12 kilograms before it fails. The required safety factor is 3. What is the greatest load the bridge should be allowed to carry during normal use?
The bridge should be allowed to carry 4 kilograms during normal use. This is because 12 kilograms divided by a safety factor of 3 equals 4 kilograms. - 11
List two types of infrastructure that civil engineers help design, and describe the purpose of each.
Infrastructure includes built systems that communities use every day.
Civil engineers help design roads, which allow people and goods to travel safely. They also help design water systems, which move clean water to homes and remove wastewater. - 12
A cantilever is a beam supported at only one end, like a diving board. Where would the beam experience the most stress: near the fixed support or near the free end? Explain your answer.
The beam would experience the most stress near the fixed support. The support must resist the bending caused by the load and the length of the beam sticking out. - 13
A city wants a new bridge that is low cost, safe, attractive, and quick to build. Explain why engineers may not be able to maximize all four goals at the same time.
A tradeoff happens when improving one goal can make another goal harder to achieve.
Engineers may not be able to maximize all four goals because design choices involve tradeoffs. For example, the safest or most attractive design may cost more or take longer to build. - 14
Look at a simple arch bridge. Explain how an arch helps carry loads compared with a flat beam.
An arch helps carry loads by spreading forces outward and downward toward the supports. This shape can reduce bending in the bridge and make good use of materials that are strong in compression. - 15
A team tests a model tower. It fails when a side joint pulls apart. What is one design change the team could make, and how should they test whether it worked?
Good engineering improvements are tested using fair comparisons.
The team could reinforce the joint with extra bracing, stronger glue, or a gusset plate. They should rebuild or repair the tower, apply the same type of load again, and compare the new failure load with the original result.