Construction and design
This domain covers joint design, static strength of welded connections, fatigue and brittle fracture. The exam tests whether you can size a weld correctly and choose the right design philosophy, not just read a weld symbol.
Static design of fillet welds
For an equal-leg fillet, throat a = 0.707 × leg length z. Design resistance per unit length is a × f_vw, where f_vw is the design weld shear strength. Effective length excludes end craters unless run-on/run-off plates are used.
Worked example
An 8 mm leg fillet, 200 mm long, single side, f_vw = 220 MPa. Throat a = 0.707 × 8 = 5.66 mm; area = 5.66 × 200 = 1,131 mm²; resistance = 1,131 × 220 = 248,800 N ≈ 249 kN. Using the leg as throat gives 8 × 200 × 220 = 352 kN, an unsafe overestimate of about 40%.
Fatigue
Fatigue is governed by stress range and detail category (EN 1993-1-9), not by static strength. The S-N curve is referenced to 2 × 10⁶ cycles, and detail category depends on geometry, weld toe quality and inspection, not steel grade. Improving toe profile or using post-weld treatment raises the category.
Brittle fracture and lamellar tearing
Brittle fracture needs tensile stress, a defect, low toughness and a constraint/thermal condition. Lamellar tearing relates to through-thickness strain in plates with inclusion content, and is addressed by joint design and Z-quality steel.
Traps
Confusing leg with throat; ignoring crater deduction; assuming higher yield steel improves fatigue; designing for static load only where cyclic loading is present.