For a partial joint penetration groove weld reinforced with a fillet weld, how is the effective throat measured?

• A. The weld length at the throat
• B. The distance from surface to root at far end
• C. The shortest distance between the groove root and the surface of the fillet
• D. The average thickness of fillet weld

Answer: (C)

The effective throat is the shortest distance through the weld from the groove root up to the surface of the reinforcing fillet. In a partial-penetration groove weld with fillet reinforcement, this minimal cross‑section thickness controls the joint’s strength, since it’s the smallest path through which shear must be carried. Measuring it as the straight-line, smallest distance from the groove root to the fillet surface captures the actual load‑carrying thickness of the welded joint. The other options describe lengths or average dimensions that do not reflect the critical cross‑section that governs strength.