Publication No. 14068
Flinn STEM Design Challenge™
Materials Included In Kit
Balsa wood, 60 cm, 100 pieces
Foam bases, 14" x 5" x 1", 12
Graph paper, 8½" x 14"
Machine bolts with nuts, 2
Steel wire, 14 gauge, 2 feet
Straight pins, 450
Wood glue, 1 oz, 6 bottles
Additional Materials Required
(for each lab group)
Gram weight set (or other weighted materials)
Rulers, metric, 2
Students should wear protective eyewear and practice lab safety when working with scissors and other tools. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAsking questions and defining problems
Planning and carrying out investigations
Constructing explanations and designing solutions
Obtaining, evaluation, and communicating information
Disciplinary Core IdeasMS-ETS1.A: Defining and Delimiting Engineering Problems
MS-ETS1.C: Optimizing the Design Solution
HS-PS2.A: Forces and Motion
HS-ETS1.B: Developing Possible Solutions
Crosscutting ConceptsScale, proportion, and quantity
Structure and function
MS-ETS1-2. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.
Answers to Prelab Questions
Answers to Questions
How Stuff Works. http://science.howstuffworks.com/engineering/civil/bridge.htm. Accessed August 2015.
How many bridges would you estimate are in the United States? A thousand? Ten thousand? Actually, over half a million bridges are used every day to cross obstacles, such as rivers, railroad tracks or valleys. Learn more about the forces that act on bridges and then design a bridge and test its load capacity.
Civil engineers are responsible for designing and supervising large construction projects, including roads, bridges and dams. They work with a team of other professionals to determine the feasibility of plans related to the cost and safety of the designs. They are primarily responsible for the basic framework and the implementation of strong, safe and long-lasting structures. When building bridges, civil engineers must take the following into account:
Two primary forces that engineers must take into account when building bridges are tension and compression. Tension is a pulling force and can cause a bridge to snap or break if not carefully monitored or accounted for. Compression acts opposite of tension and is a pushing force. If compression puts too much stress onto the bridge, it will buckle (see Figure 1). Other, less common but equally devastating forces that act on bridges include torsion, shear stress and resonance. Torsion specifically affects suspension bridges and causes the roadway to rotate and twist like a rolling wave. This is typically due to high winds. Shear stress can rip a bridge apart when two fastened structures are forced in opposite directions. Finally, resonance occurs when unchecked vibrations increase and travel through the bridge in the form of destructive waves.
Three of the most common bridges are beam bridges, arch bridges and suspension bridges. Each bridge has its own unique characteristics, strengths and weaknesses. A bridge made as the result of a combination of these basic bridge types is called a composite bridge. A beam bridge has a simple design—a horizontal beam with piers at each end (see Figure 2). Rarely will they span over 60–75 meters due to tension and compression. The piers support the downward force of gravity, load and weight of the bridge itself. The further apart the piers, the weaker the bridge is and more likely to succumb to buckling or snapping. Engineers have developed methods to dissipate or spread out the forces. By increasing the height of the beam or adding latticework (a truss system of triangles), tension is dissipated strengthening the bridge.
Arch bridges are some of the oldest bridges, designed by ancient Romans over 2,000 years ago. These bridges will span distances of 60–245 meters. The design allows the forces to act against themselves creating a very stable, long lasting bridge (see Figure 3). By design, the forces are spread outward by the curvature and are concentrated on the abutments—supports for the arch bridge. Tension is not a major concern with an arch bridge unless the curvature is extended too far (i.e., the arch is too large). The greatest challenge to building an arch bridge is maintaining structural integrity during the building process. Until the two converging sides join in the middle, the bridge is very unstable.
The suspension bridge has the ability to span vast distances of 600–2,100 meters. This design suspends the roadway from steel cables that drape over two towers and are ultimately secured to anchorages. A deck truss is built beneath the roadway to avoid torsion. The load on the roadway is transferred through the steel cables via tension force and then toward the towers and the anchorages and lastly to the ground (see Figure 4).
The purpose of this activity is to design and build a bridge that will be tested for its ability to carry a load. Small weights will be added to the bridge until the bridge breaks.
Balsa wood, 15 sticks
Foam base, 14" x 5" x 1", 2
Individual Design Worksheets, 3
Straight pins, box of 75
Wear protective eyewear while cutting balsa wood and testing the bridges. Special precaution should be taken when cutting the wood with scissors or removing pins with the use of pliers. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.
Part A. Bridge Specifications
Student Worksheet PDF