Simulations / Engineering

Bridge Truss Load Tester

Design a craft-stick truss, put a weight at the center, and watch the forces flow through every member. Blue members are in tension, red members are in compression. The first member to reach its limit sets the bridge's strength.

Design

Test

Failure load
Weak link
Bridge mass
grams of sticks
Load ÷ bridge weight
strength-to-weight
Model: a Warren truss solved by the method of joints, a single point load at midspan, craft-stick members (E ≈ 10 GPa, 2 × 10 mm). Compression limit is Euler buckling, tension limit is the glued joint (about 80 N per stick), both scaled by joint quality. Self-weight is ignored. Real glued bridges usually reach only a fraction of these loads because of imperfect cuts, uneven glue, and off-center loading, and real bridges also fail at joints and by twisting.

Try this

  • Increase truss depth. Which members get less force, and which get more?
  • Add sticks per member. Does the failure mode change?
  • Compare 4 panels and 10 panels at the same depth. Why do short members help against buckling?

What to notice

  • Top members squeeze and bottom members stretch; diagonals carry shear.
  • Long compression members buckle at loads far below their material strength.
  • The best design balances all members so none fails far ahead of the others.

Connect to the lab