These assumptions ensure that every member in the truss is a two-force member, meaning it is either in pure tension (pulling away from the joint) or pure compression (pushing toward the joint). Step 1: Determine External Support Reactions
| Mistake | Consequence | |---------|-------------| | Drawing member force wrong direction in FBD | Sign reversal (tension vs compression swapped) | | Forgetting to convert angles correctly | Wrong force components | | Using joint with >2 unknowns | Cannot solve – stuck | | Misidentifying support reaction type (e.g., roller has vertical only) | Wrong reaction values propagate | | Using method of sections but cutting through >3 unknown members | Unsolvable without extra equations | 2.1.7 calculating truss forces