Recommended for High School and K-8.
A truss is a rigid framework whose internal members are connected in a triangular pattern. Trusses have a very high strength-to-weight ratio, which allows them to span long distances. Historically, trusses were frequently used in bridge design, but are becoming common elements for roof and floor framing in home construction due to their efficiency and low cost.
Bridges must carry three different kinds of forces: loads (the external forces applied to the bridge, such as the weight of cars, trucks, rain, and snow), reactions (the support forces supplied by the abutments or piers), and internal forces (the tension and compression forces developed along structural members when a load is applied). Truss bridges are statically determinate. Their support forces are equal to the applied load, and the moments about any point are zero. The strength of a bridge is determined by the largest internal force it can withstand before failing, the material used in fabrication, and the width and thickness of individual structural members.
- Build a truss bridge that spans 24 inches.
- Measure the tensile and compressive forces in individual structural components.
- Measure the ultimate load-carrying capacity of the bridge.