Weld Design — validation & limitations

What it calculates

• EN 1993-1-8 fillet and butt weld strength check — directional method (§4.5.3.2), both conditions
• Full-penetration butt welds additionally capped at the parent metal's yield strength
• Safety factor and utilisation ratio for direct shear, bending, torsion and combined loading
• Weld fatigue life — EN 1993-1-9 two-slope S-N curve with the γ_Mf partial factor, the constant-amplitude fatigue limit, the 10⁸ cut-off and Miner damage accumulation
• ISO 5817 weld imperfection acceptance levels (B / C / D) with a defect-by-defect table
• Heat input and t8/5 cooling time per EN 1011-1 / EN 1011-2 Annex D (3-D and 2-D regimes)
• Weld group eccentric in-plane load — rectangular group polar moment with corner-resolved vector shear

Standards this tool applies

• EN 1993-1-8 — Simplified EN 1993-1-8 §4.5.3.2 directional method for fillet and butt welds (plus a linear shear screen, β_Lw and the short-weld flag) — σ⊥, τ⊥, τ∥, equivalent stress, utilisation and safety factor under direct shear, bending, torsion and combined loading.

Validation evidence — independent reference cases (1)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

• Full-penetration butt weld in bending, perpendicular-stress condition

  Agrees

  Source: EN 1993-1-8:2005 §4.7.1(1) and §4.5.3.2 eq. 4.1; EN 1993-1-1 §6.1; Shigley 10th ed. Table 9-2 case 1

  Inputs: butt_full, throat 10 mm, L 200 mm, M 5.0e6 N·mm, S355 / A572-Gr50 (fu 448, fy 345 MPa), gamma_M2 1.25

  Quantity	Reference value	Tolerance
  sigma_perp (MPa)	75.000	1e-6 relative
  0.9·fu/gamma_M2 cap (MPa)	322.56	1e-6 relative
  utilisation (perp governs)	0.2325149	1e-6 relative
  SF	4.3008	1e-6 relative

  Conservative simplification: The engine applies the fillet-weld perpendicular-stress condition to butt welds as well and uses the lower fu of 448 MPa for the S355 row; both are stated conservative choices that the reference follows.

  tests/golden/REF-welds-butt-perp-condition.golden.test.ts

Limitations

Conservative simplifications

• Full-penetration butt weld in bending, perpendicular-stress condition — The engine applies the fillet-weld perpendicular-stress condition to butt welds as well and uses the lower fu of 448 MPa for the S355 row; both are stated conservative choices that the reference follows.

Not checked by this tool

• Bolted connections and base plates (EN 1993-1-8 clauses 3 and 6) — Not implemented; check bolts with /bolts and base plates by the EN 1993-1-8 component method
• Moment-resisting joints: component method, stiffness and classification — Not implemented; use EN 1993-1-8 section 6 or connection-design software
• Connected plates next to a fillet weld (plate yield, block tearing) — Only the weld throat is checked (a full-penetration butt weld is capped at the parent metal); check the plates to EN 1993-1-8
• Hollow-section joints (EN 1993-1-8 section 7) — Not implemented; use EN 1993-1-8 section 7 for RHS / CHS joints
• Lamellar tearing (through-thickness properties) — Not assessed; select a Z-quality steel per EN 1993-1-10 for loaded T-joints
• Brittle fracture: steel sub-grade for thickness and temperature — Select the toughness sub-grade per EN 1993-1-10
• The lower f_u of a THICKER joined part over 40 mm — Only the thinner plate t_min is an input and the rows hold f_u for t <= 40 mm; a thicker part over 40 mm can over-state f_u by up to about 4 % (S420 520 -> 500 MPa) - check with that part's EN 1993-1-1 Table 3.1 f_u