Construction and Design of Welded Structures
This domain tests whether you can size a weld for static load, classify a detail for fatigue, and read a weld symbol without ambiguity.
Static design
For fillet welds, the design throat is 0.7 × leg length for equal-leg 90° fillets. Design resistance uses the throat area, the weld design strength and a partial safety factor. Weld groups are treated by the directional method (resolving forces and comparing to strength) or the simplified method (comparing resultant to a reduced strength). For butt welds, full-penetration welds are usually taken as matching the parent metal; partial-penetration welds must be checked on the actual throat.
Fatigue design
Nominal-stress fatigue uses detail categories (FAT classes) from S–N curves. Slopes are typically m = 3 for 10⁴–5×10⁶ cycles and m = 5 beyond, with a constant-amplitude limit and a cut-off. Weld toe geometry, lack of penetration, undercut and attachments define the class. Post-weld toe treatment improves class but does not remove the need for correct detailing.
Worked example
A 6 mm equal-leg fillet, 200 mm long, carries a design shear force. Throat = 0.7 × 6 = 4.2 mm. With a design weld shear strength of 208 MPa, resistance per mm = 4.2 × 208 = 874 N/mm. For 200 mm: 874 × 200 = 174.8 kN. Applied load 120 kN gives utilisation 120/174.8 = 0.69. Reasoning: keep units consistent (N and mm), and do not deduct end craters unless the standard requires it.
Traps
Using leg length as throat. Mixing allowable-stress and limit-state codes. Applying static utilisation to a fatigue-loaded detail. Forgetting that weld symbols on drawings are governed by ISO 2553 conventions (arrow side/other side, tail for process).