Weld Design Checklist

Checklist for welded connection calculations and drafting: throat/effective length, directionality, minimums, and documentation.

Welded connections have a unique failure mode: the assumptions that drive the calculation (weld type, throat dimension, effective length) are often invisible in the final product. Unlike bolts, you cannot count welds or measure them easily after fabrication. This makes the documentation trail especially important.

Common sources of error in weld calculations include: mixing up leg size and throat thickness, ignoring minimum weld size requirements, applying the wrong directionality factor, and misinterpreting eccentric weld group behavior. This checklist targets those specific pitfalls.

For the full general verification workflow (units, replication strategy, sensitivity testing, and archiving), see How to verify calculator results.

Before You Start

Collect these inputs before checking any welded connection:

• Weld demand: Resolve the connection forces into components acting on the weld: longitudinal shear (parallel to weld axis), transverse shear (perpendicular to weld axis), and normal force (perpendicular to the throat). For eccentric weld groups, you also need the eccentricity to compute the torsional component.
• Weld type and size: Fillet weld (leg size) or groove weld (complete joint penetration or partial joint penetration). For fillet welds, know the leg size and whether equal-leg or unequal-leg. For groove welds, know the effective throat and the groove preparation.
• Electrode classification: E70XX (FEXX = 70 ksi) for AISC, E48XX (fuw = 480 MPa) for AS 4100, or the matching electrode for EN 1993. The electrode strength directly scales the weld capacity.
• Base metal thicknesses: The thicker part joined determines the minimum fillet weld size. The thinner part limits the maximum weld size along an edge.
• Weld length and pattern: Total effective weld length, deducting any crater (start/stop) lengths if required by the standard. For weld groups, know the pattern geometry (L-shape, C-shape, rectangular, etc.) and the centroid location.
• Weld category (AS 4100 only): SP (structural purpose, phi = 0.80) or GP (general purpose, phi = 0.60). This choice significantly affects capacity and depends on the inspection and qualification requirements.

Step-by-Step Design Process

Step 1 — Determine weld demand per unit length. Divide the total connection force by the effective weld length to get demand per unit length (kip/in or N/mm). For eccentric weld groups, use the elastic method or instantaneous center of rotation method to find the peak demand on the critical weld element.

Step 2 — Compute weld capacity per unit length. For fillet welds per AISC 360-22 Section J2.4: phi Rn = phi x 0.6 x FEXX x te, where phi = 0.75, te = 0.707 x leg size (equal-leg), and FEXX = electrode tensile strength. For E70XX with a 1/4-in fillet: phi Rn = 0.75 x 0.6 x 70 x 0.707 x 0.25 = 5.57 kip/in.

Step 3 — Apply directionality factor (if applicable). AISC 360 Section J2.4 allows a 50% increase for transverse fillet welds: phi Rn = phi Rn,longitudinal x (1.0 + 0.50 sin^1.5 theta), where theta is the angle between the weld axis and the force direction. At theta = 90 degrees (pure transverse): factor = 1.50. AS 4100 and EN 1993 do not provide the same enhancement.

Step 4 — Check minimum weld size. Per AISC Table J2.4: minimum leg size depends on the thicker part joined. For material up to 1/4 in: 1/8 in min. For 1/4 to 1/2 in: 3/16 in. For 1/2 to 3/4 in: 1/4 in. For over 3/4 in: 5/16 in. This is a detailing requirement independent of strength.

Step 5 — Check maximum weld size. Per AISC J2.2b: along edges of material 1/4 in or more thick, the maximum fillet weld size is t - 1/16 in (where t is the edge thickness). Along edges less than 1/4 in, the weld may equal the edge thickness.

Step 6 — Check base metal capacity. The weld should not be stronger than the base metal it connects. Check the base metal shear rupture strength: phi Rn = phi x 0.6 x Fu x t per unit length (phi = 0.75). If the base metal controls, increase the plate thickness or reduce the weld size.

Step 7 — Document the weld. Record weld type, leg size, electrode, effective length, inspection category, and governing standard. Include the AWS A2.4 weld symbol on the connection drawing.

Worked Example

Given: A bracket plate (PL 1/2 x 8 x 12, A36, Fy = 36 ksi, Fu = 58 ksi) is welded to a column flange with fillet welds on both sides of the plate, loaded in shear. Applied factored load: Vu = 80 kips. Weld runs vertically along both 12-in edges. E70XX electrode.

Step 1 — Weld demand:

• Total weld length = 2 x 12 = 24 in
• Demand per inch = 80 / 24 = 3.33 kip/in

Step 2 — Trial weld size 3/16 in:

• te = 0.707 x 0.1875 = 0.1326 in
• phi Rn = 0.75 x 0.6 x 70 x 0.1326 = 4.18 kip/in
• 4.18 > 3.33. OK (ratio = 0.80).

Step 3 — Directionality: Load is parallel to the weld axis (longitudinal shear), so theta = 0 degrees. No directionality enhancement. Factor = 1.0.

Step 4 — Minimum weld size: Thicker part = column flange (assume 3/4 in or thicker) = minimum 1/4 in. But the bracket plate is 1/2 in, so the minimum based on the thicker of the two parts joined: for 1/2 in, minimum = 3/16 in per AISC Table J2.4. Our 3/16-in weld meets the minimum.

Wait — the column flange is likely > 3/4 in (e.g., W14x61 has tf = 0.645 in, so 1/2 to 3/4 range, minimum = 1/4 in). Let's use 1/4-in weld instead.

Revised — 1/4-in fillet weld:

• te = 0.707 x 0.25 = 0.177 in
• phi Rn = 0.75 x 0.6 x 70 x 0.177 = 5.57 kip/in
• Ratio = 3.33 / 5.57 = 0.60. OK.

Step 5 — Maximum weld size: Along the 1/2-in plate edge: max = 1/2 - 1/16 = 7/16 in. Our 1/4-in weld is within the limit.

Step 6 — Base metal check (bracket plate):

• phi Rn = 0.75 x 0.6 x 58 x 0.50 = 13.1 kip/in >> 3.33 kip/in. OK.

Result: Use 1/4-in E70XX fillet weld on both sides of the bracket plate, 12 in long each side. Governing utilization = 0.60.

Common Pitfalls

1. Confusing leg size and throat. For equal-leg fillet welds, the effective throat = 0.707 x leg size. Entering the leg size where the throat is expected (or vice versa) changes the capacity by 41%. This is the most common weld calculation error.

2. Ignoring minimum weld size. A weld can pass a strength check but fail the minimum size requirement. Minimum size exists for metallurgical reasons (adequate heat input for fusion) and is mandatory regardless of demand.

3. Applying the AISC directionality factor when the code does not allow it. AISC 360 allows a 50% increase for transverse fillet welds. AS 4100 and EN 1993 do not provide this enhancement. If you are designing to AS 4100 or EN 1993 and apply the AISC 1.5 factor, the weld is unconservative.

4. Neglecting weld group eccentricity. When the load does not pass through the weld group centroid, torsional shear develops in the weld. This can increase the peak weld stress by 50-100% compared to direct shear alone. Always check for eccentricity.

5. Forgetting end returns. For fillet welds that terminate at an edge, most codes require a return of 2x the weld leg size around the corner to prevent stress concentrations and cracking at the weld termination.

6. Using GP category when SP is required (AS 4100). SP (phi = 0.80) requires NDT inspection and welder qualification. GP (phi = 0.60) is for general-purpose welds with visual inspection only. Using GP for a primary structural connection reduces capacity by 25% compared to SP, or using SP when the fabrication cannot deliver the required quality is non-compliant.

Code Comparison

Geometry & symbol documentation

• Weld type is specified (fillet/groove/etc.) and matches the detail drawing.
• Effective length rules are considered (short weld effects, end returns if relevant).
• Weld symbol matches the intended side (arrow/other side) and any all-around/field indicators.
• Minimum weld size requirements are checked against base metal thickness and WPS constraints.
• For fillet welds, confirm whether you are working with leg size or effective throat (they differ by a factor of ~0.707 for equal-leg fillets).

Demand definition

• Resolve actions into weld demand components with a consistent sign convention.
• For eccentric weld groups, confirm whether the method accounts for torsion/secondary effects.
• Identify whether the loading is primarily longitudinal or transverse to the weld axis (this affects the directionality enhancement in some codes).

Material and procedure

• Electrode/filler assumptions are documented (e.g., E70XX for AISC, E48XX for AS).
• Inspection category and acceptance criteria are outside the calculator scope; record them separately.
• Preheat and interpass temperature requirements depend on material and thickness; note if applicable.

Documentation

• Store the weld symbol output with a note referencing the project WPS/spec.
• Record the governing standard and edition (weld capacity formulas differ significantly between AISC, AS 4100, EN 1993, and CSA S16).
• Archive inputs and outputs with a date stamp for reproducibility.

Frequently Asked Questions

Why do weld calculators give different results for the same weld size? The most common reason is the directionality factor. Some codes (e.g., AISC 360) enhance transverse fillet weld capacity by up to 50%, while others do not. If one calculator applies the enhancement and another does not, results will differ even with identical inputs.

What is the difference between leg size and throat thickness? For an equal-leg fillet weld, the effective throat is approximately 0.707 times the leg size. Some inputs ask for leg size, others for throat. Mixing them up changes the calculated capacity by ~30%.

Should I always check minimum weld size? Yes. Minimum weld size is a detailing requirement that exists independently of the strength calculation. A weld can pass a strength check but still violate minimum size rules based on the thicker part joined.

Does the calculator handle weld group eccentricity? The calculator uses an elastic weld group analysis method with torsional components. For large eccentricities or non-standard patterns, verify results against an independent method.

Is this checklist engineering advice? No. It is a documentation and QA pattern to help reduce errors and improve traceability. Project criteria and compliance decisions are defined by the governing standard and the engineer of record.

What is the minimum fillet weld size for joining a 5/8-inch plate to a 1-inch plate per AISC Table J2.4? Per AISC 360-22 Table J2.4, the minimum fillet weld size is based on the thicker part joined. For material thickness over 3/4 inch (19 mm), the minimum fillet weld leg size is 5/16 inch (8 mm). For the 5/8-inch plate, the thicker part is 1 inch, so the minimum weld is 5/16 inch. Note that the weld need not exceed the thickness of the thinner part (5/8 inch = 0.625 in), which is not a constraint here. The maximum fillet weld size along the edge of material 1/4 inch or more thick is t_material − 1/16 inch per J2.2b, so for the 5/8-inch plate the maximum weld along its edge is 5/8 − 1/16 = 9/16 inch.

What is the capacity per inch of a 3/16-inch E70XX fillet weld per AISC 360 (LRFD)? For a 3/16-inch (0.1875 in) fillet weld with E70XX electrode (FEXX = 70 ksi), the effective throat te = 0.707 × 0.1875 = 0.1326 in. Design strength per inch: φRn = φ × 0.6 × FEXX × te = 0.75 × 0.6 × 70 × 0.1326 = 4.18 kip/in (for longitudinal or transverse shear without directionality enhancement). With the directional strength increase for a transversely loaded weld: φRn = 4.18 × (1.0 + 0.50 × sin^1.5 θ) = 4.18 × 1.5 = 6.27 kip/in at θ = 90°. This 50% enhancement for transverse welds per AISC 360 Section J2.4 is a significant difference from codes that do not apply it.

Run This Calculation

→ Welded Connection Calculator — fillet and groove weld capacity per AISC 360, AS 4100, EN 1993, and CSA S16 with SP/GP category selection.

→ Weld Symbol Generator — create AWS A2.4 weld symbols for drawings with correct tail notes.

→ Gusset Plate Calculator — combined weld group and plate design for bracing connections.

Related pages

• Guides and checklists
• Welded connections calculator
• Weld symbol generator
• Minimum fillet weld size — AISC J2.4 & AS 4100 table
• Fillet weld size selection — AISC 360 min/max limits
• Fillet weld size chart — capacity per unit length, E70XX
• Weld electrode reference — E60XX, E70XX, E80XX classifications
• Weld symbol chart — AWS A2.4 reference
• Steel Fy & Fu reference — yield and tensile strength by grade
• Steel grades reference
• How to verify calculator results
• Disclaimer (educational use only)

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.