Fillet Weld Strength Calculator

What this tool does

Tabulates fillet weld strength per inch of weld for every standard leg size, E60 through E120. Select a size, enter a length, and the tool returns the total weld capacity with an optional load check.

Strength is shear on the effective throat, t_e = 0.707w, divided by Ω = 2.00 for the ASD allowable. This is a weld-metal strength check, not a complete connection design.

Formula

Leg size w, effective throat t_e and effective length L_e in inches; F_EXX in ksi. Rn and Ra are total strengths in kip; the table prints them per unit weld length, in kip/in.

Assumptions

The displayed result is a weld-metal strength check based on static loading. It is not a complete connection design.

• Inputs: electrode classification F_EXX (E60–E120), fillet leg size w, and weld length. F_EXX is the specified tensile strength of the classification; E70 is the common structural default.
• Weld geometry: standard equal-leg 45° fillet. Unequal legs, deep-penetration fillets and groove welds are outside the tool.
• Design method: ASD, Ra = Rn / Ω at Ω = 2.00. Never size a weld off the nominal value.
• Per inch against total: the table is strength per unit weld length; total strength is that value times the effective length.
• Directional strength: the AISC directional-strength increase is not used, so the result is conservative where the increase applies.
• Load input: the check is on the resultant load. Parallel and transverse components are shown for information only.
• Weld length: the entered length is used as the effective length. AISC effective-length limits are flagged, not applied.

Basis

• The throat, not the leg, a fillet fails across its smallest section, the effective throat. For a standard 45° fillet that plane is 0.707 times the leg, so strength is referenced to it whatever the leg dimension called out.
• Weld-metal limit state, the weld-metal limit state is shear on the effective throat, taken as 0.60·F_EXX of the deposited metal.
• Directional strength, AISC permits an increase in nominal weld strength for fillet welds loaded at an angle to the weld axis, worth up to 50% on a fully transverse weld.
• Electrode selection, the electrode must be compatible with the base metal, the welding procedure, the process and the governing welding requirements. Compatibility is not a matter of matching F_EXX to the base-metal Fy or Fu.

Worked example

Weld size limits

• Minimum, governed by the larger of the size required to transmit the force and the applicable AISC minimum, which is tied to the thickness of the thinner connected part.
• Maximum, for material less than 1/4 in. thick, generally the material thickness; for material 1/4 in. thick or greater, generally the material thickness less 1/16 in., unless otherwise designated.

Weld length

Effective length is not always the length laid down, and strength does not go on increasing with length. Three thresholds, all measured against the weld size w:

• L < 4w, a fillet shorter than four times its size does not develop its full throat over that length, and AISC limits the effective size accordingly. Lengthen the weld or reduce the size assumed in design.
• L > 100w, stress along an end-loaded fillet peaks at the ends and drops through the middle, so AISC reduces the effective length past this point.
• L > 300w, AISC holds the effective length at a fixed value beyond this, whatever the weld actually measures.
• Where a run must be long, transverse welds, a balanced weld group, or splitting the force between more welds is usually better than extending one end-loaded fillet.

Considerations

Each item the calculator leaves out, and what it requires instead.

• Connected material, base-metal shear yielding and rupture along the weld, block shear, net-section rupture and connected-element limit states are checked separately, and any of them can govern ahead of the weld metal.
• Weld groups and eccentricity, eccentric load, moment and torsion redistribute force between welds, so a uniform kip/in does not apply. Complex weld geometry needs a weld-group analysis.
• Dynamic and cyclic loading, impact, vibration, cyclic and fatigue loading are assessed under the applicable fatigue and dynamic-loading provisions, not by scaling a static allowable.
• Overhead lifting, lifting lugs, spreader beams and below-the-hook weldments are designed under the applicable lifting requirements, which impose their own design factors above a structural ASD allowable.

Field notes

• Balance the group. Place welds symmetrically about the load line where possible to minimize eccentric loading.
• Develop the part, not the page. Size the weld for the force the connected element must transfer; a weld stronger than the part adds no capacity.
• Minimum size is a code floor. A weld may be adequate for the applied load but still be undersized for the connected material.
• Access matters. Overhead or restricted-access welding can affect what can be practically and properly made.
• A calculated weld is not necessarily a sound weld. Confirm the procedure, electrode, qualification, inspection, and acceptance criteria against AISC 360 and AWS D1.1/D1.1M.
• Visual inspection has limits. A weld may appear acceptable visually while containing subsurface or otherwise hidden discontinuities. Where required by the design, specification, or governing code, NDT methods such as MPT or UT may be necessary to evaluate weld quality.
• Moving loads require additional consideration. Impact, vibration, cyclic loading, fatigue, and overhead lifting require applicable design provisions and factors beyond these static values.

References

Primary references: ANSI/AISC 360, Chapter J; AISC Steel Construction Manual; AWS D1.1 Structural Welding Code, Steel.