1. Truss Assumptions
Members are two-force members connected at frictionless pins. Loads act only at joints.
2. Support Reactions
Pin: resists both Rx & Ry. Roller: resists only Ry (vertical).
3. Equilibrium at each Joint
Σ Fx = 0 and Σ Fy = 0 must hold simultaneously.
4. Sign Convention
Tension (T): member pulls away from joint (+).
Compression (C): member pushes into joint (−).
Zero-force: enter 0 in the magnitude field.
5. Zero-Force Member Rules
Rule 1: Two non-collinear members at an unloaded joint → both zero.
Rule 2: Three members at unloaded joint, two collinear → third is zero.
6. Colour Key
🟥 Red = Tension | 🔵 Blue = Compression | 🟡 Gold = Zero-force | ⬜ White = Unsolved