Welding — Cheat Sheet
Fillet & groove weld strength, weld-as-a-line, allowable stress.
Weld symbol: the arrow points at the joint; symbols below the reference line are the arrow side, above the other side.
Fillet welds
| Effective throat | a = 0.707·leg |
| Direct shear | τ = P / (0.707·leg·L) |
| Size for load | leg = P / (0.707·L·τ_allow) |
Weld groups (as a line)
| Rectangular box | A_w = 2(b+d), J_u = (b+d)³/6 |
| Circular | A_w = πD, J_u = πD³/4 |
| Combined stress | τ_r = √(τ_direct² + τ_torsion²) |
Butt / groove welds
| Tension/compression | σ = P / (t·L) |
| Shear | τ = P / (t·L) |
| t | effective throat = plate thickness (full pen) |
Practice
| Allowables | per AWS D1.1 / D17.1 (aerospace) |
| Symbols | arrow-side below, other-side above the reference line |
| Fatigue | weld toes are stress raisers — grind for fatigue |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.