Lesson 3: Structural Engineering
Structural engineers design the bones of civilization — the bridges, tunnels, skyscrapers, and stadiums that define our built environment. Every structure is a calculated balance of forces.
Key Concepts
Dead Load and Live Load
Dead load is the permanent weight of the structure itself. Live load is the changing weight it carries — people, vehicles, snow. Engineers design for both, plus a safety factor in case loads are higher than expected.
Trusses
A truss is a framework of triangles used to span long distances efficiently. Bridge trusses, roof trusses, and tower cranes all use this principle. The triangles distribute forces through compression and tension members.
Failure Modes
Structures fail in specific ways: buckling (slender columns collapsing sideways under compression), fracture (materials cracking under tension), fatigue (repeated loading causing gradual cracking), and settlement (foundations sinking). Engineers design to prevent all of them.
🆕 Bridge Load Tester
Add load to your bridge and see which members fail first!
✅ Check Your Understanding
1. What is live load?
2. Why do trusses use triangles?
3. What is buckling?