Material properties, shared by every verification. The cross-section is not shared: SIA 263 classifies it from the internal forces, so it belongs to each verification and appears with it.
Checks a welded joint with fillet, partially or fully penetrated welds, to SIA 263:2013: the throat section and the contact sections against the design force, then the construction rules for the runs and the throat. Every step shows its formula and the clause it comes from.
You enter fy,k (clause 3.2.2.3) and fu,k (table 1) of the parts, the tensile strength of the filler metal fuE (equation (87)), in general 510 N/mm², and γM1 and γM2 (clause 4.1.3). You choose the type of weld with its throat or legs, and the joint and its runs: for example a T-joint with a fillet on each side or on one side only, or a lap joint with two side fillets and an end fillet. You enter the width b1 and thickness t1 of the attached plate, the thickness t2 of the plate it is welded to, the length l of each side fillet, and FEd as a resultant or as components Fx, Fy and Fz.
You get the effective length, the strengths of the throat and the contact sections, βLw, the utilisation of each check with a pass or fail, the governing section and the throat required. For comparison it reports the resistance of EN 1993-1-8 clause 4.5.3.3 and that of the attached plate, t1 · b1 · fy,k/γM1 (clause 5.1.2.1). With the Basic plan, it prints as an A4 calculation note.
A lap joint with two side fillets of l = 250 mm and an end fillet across a plate b1 = 150 mm wide, both plates 20 mm thick, with equal legs and a = 7 mm, in fy,k = 355 N/mm², fu,k = 470 N/mm² and fuE = 510 N/mm², under FEd = 1,014 kN. These are the module's own results for its worked example, computed when this page was built.
| Input | Value | Ref. |
|---|---|---|
| Characteristic yield strength of the parts fy,k | 355 N/mm² | § 3.2.2.3 |
| Characteristic tensile strength of the parts fu,k | 470 N/mm² | § t.1 |
| Tensile strength of the filler metal fuE | 510 N/mm² | § (87) |
| Resistance factor, gross sections γM1 | 1.05 | § 4.1.3 |
| Resistance factor, welds γM2 | 1.25 | § 4.1.3 |
| Type of weld | Fillet weld, equal legs — a entered | § 6.3.1.8 |
| Throat thickness a | 7 mm | § 6.3.2.6 |
| Joint and runs | Lap joint — two side fillets and an end fillet | § 6.3.2.5 |
| Width of the attached plate b1 | 150 mm | |
| Length of each side fillet l | 250 mm | § 6.3.2.5 |
| Thickness of the attached plate t1 | 20 mm | § 6.3.6.3 |
| Thickness of the plate welded to t2 | 20 mm | § 6.3.6.4 |
| Force on the weld | Resultant entered | § 6.3.2.1 |
| Design force carried by the weld FEd | 1014 kN | § 6.3.2.1 |
| Step | Value | Ref. |
|---|---|---|
| Design forceThe resultant, entered. | FEd = 1,014.0 kN | § 6.3.2.1 |
| Throat thicknessEntered. | a = 7.00 mm | § 6.3.2.6 |
| Smaller contact widtha·√2: both legs of the isosceles triangle. | smin = 9.90 mm | § (88) |
| Effective length2·l + b1: the two side fillets and the end fillet. | Σl = 650 mm | § 6.3.2.5 |
| Force per unit lengthTaken uniform along the runs. | FEd/Σl = 1,560.0 N/mm | § 6.3.1.7 |
| Strength of the throat section0,6·fuE. | fw = 306 N/mm² | § (87) |
| Strength of the contact section0,8·fy,k. | fs = 284 N/mm² | § (88) |
| Reduction for a long lap joint1,2 − 0,2·Lj/(150·a) ≤ 1,0 with Lj = l = 250 mm and 150·a = 1,050 mm: no reduction. | βLw = 1.000 | § 6.3.5.1 |
| Step | Value | Ref. |
|---|---|---|
| Throat sectionFEd ≤ βLw·a·Σl·fw/γM2 | η = 0.910 · Pass91 % of the capacity used | § (87) |
| Step | Value | Ref. |
|---|---|---|
| Contact sectionFEd ≤ βLw·smin·Σl·fs/γM2 | η = 0.694 · Pass69 % of the capacity used | § (88) |
| Step | Value | Ref. |
|---|---|---|
| Length of the runsl ≥ 40 mm | η = 0.267 · Pass27 % of the capacity used | § 6.3.6.2 |
| Step | Value | Ref. |
|---|---|---|
| Maximum throata ≤ 0,7·tmin | η = 0.500 · Pass50 % of the capacity used | § 6.3.6.3 |
| Step | Value | Ref. |
|---|---|---|
| Minimum throata ≥ amin | η = 0.714 · Pass71 % of the capacity used | § 6.3.6.4 |
| Governing sectionFor equal legs the throat governs when 0,6·fuE < √2·0,8·fy,k: 306 against 402 N/mm². | – = Throat | § (87), (88) |
| Throat required(87) and (88) solved for a, equal legs. | areq = 6.37 mm | § (87), (88) |
| EN 1993-1-8 would givefu,k·a·Σl/(√3·βw·γM2)·βLw, βw = 0.90.for comparison | Fw,Rd = 1,097.5 kN | EN 1993-1-8 4.5.3.3 |
| Resistance of the attached platet1·b1·fy,k/γM1, for comparison: the weld is at least as strong as the plate. | Npl,Rd = 1,014.3 kN | § 5.1.2.1 |
Verified clause by clause against SIA 263:2013 and against independent calculations used on real projects, before release.
For equal legs the throat governs when 0.6 · fuE < √2 · 0.8 · fy,k. In the worked example that is 306 against 402 N/mm², so the throat governs, η = 0.910 against 0.694 on the contact section. Equations (87) and (88) solved for a give areq = 6.37 mm.
For comparison only. fu,k · a · Σl/(√3 · βw · γM2) · βLw, with βw = 0.90, gives Fw,Rd = 1,097.5 kN in the worked example. The checks are those of SIA 263, equations (87) and (88).
The full calculation is shown on screen, free and without an account. A print-ready A4 calculation note is part of the Basic plan.
Norm: SIA 263:2013 · Page updated: 8 November 2026