Construction and design
This domain tests whether you can read a weld symbol, size a weld correctly and understand why details fail. Expect ISO 2553 symbols, effective throat, static design of fillet and butt welds, fatigue-sensitive details, and the link between design detail and inspectability.
Symbols and joint design
ISO 2553 uses an arrow line, a continuous reference line and a dashed identification line. A symbol above the reference line refers to the arrow side; below it refers to the other side. The tail carries process or specification information. Full-penetration butt welds need edge preparation, backing or root treatment, and must be specified unambiguously.
Sizing fillet welds
For a 90-degree fillet the throat is a = 0.707 z, where z is the leg length. Effective length excludes end craters unless run-on and run-off plates are used. Static design to EN 1993-1-8 uses Fw,Rd = fvw,d x a, with fvw,d = fu/(sqrt3 x beta_w x gamma_M2). The correlation factor beta_w is 0.80 for S235, 0.85 for S275 and 0.90 for S355.
Worked example
A double-sided 6 mm fillet in S275 with fu = 410 N/mm squared, gamma_M2 = 1.25: a = 0.707 x 6 = 4.2 mm. fvw,d = 410/(1.732 x 0.85 x 1.25) = 222.8 N/mm squared. Resistance per weld = 222.8 x 4.2 = 936 N/mm; two welds give about 1.87 kN/mm. Reasoning: the leg is not the throat, and the beta_w and gamma_M2 factors must be applied before multiplying by throat thickness.
Fatigue and inspectability
Fatigue strength depends mainly on detail geometry, not weld size alone: misalignment, undercuts and abrupt section changes lower the detail category. Toe grinding can improve it. Design must leave access for visual inspection and, where required, ultrasonic testing.
Traps that cost marks
- Confusing leg length with throat thickness.
- Placing the symbol on the wrong side of the reference line.
- Counting deep penetration as extra throat without a qualified procedure.
- Using static weld resistance for a fatigue-loaded detail.