Weld Group Calculator
This weld group calculator evaluates an eccentrically loaded fillet weld and returns the weld group coefficient C, the controlling weld stress, the required weld leg size, and the capacity ratio. It builds the weld outline for L-shape, C-shape, or rectangular patterns from your width and height, then integrates the direct and moment stresses along the weld to find the worst-stressed point. Capacities use the AISC fillet weld strength of 0.75 · 0.6 · Fexx · 0.707 · leg per inch of weld.
Formula
φRn (per inch) = 0.75 · 0.6 · Fexx · 0.707 · w ; Capacity = C · L · φRn
- C
- Weld group coefficient = 1 / (maximum unit stress × total weld length) under a unit load
- Fexx
- Electrode tensile strength in ksi: 60, 70, 80, or 90
- w
- Fillet weld leg size in inches (0.707·w is the effective throat)
- L
- Total length of all weld segments in inches
- 0.75
- AISC resistance factor for fillet welds
How it works
- Choose the weld pattern (L-shape, C-shape, or rectangular) and enter its width and height in inches. The calculator lays out the weld segments and locates the group centroid.
- Enter the eccentricity of the load from the centroid (inches), the load magnitude in kips, and the load angle from vertical. An elastic vector analysis along the weld finds the maximum unit stress and the coefficient C.
- Select the electrode (E60XX through E90XX) and weld leg size. The tool reports C, the required leg size rounded to the nearest 1/16 inch, the total weld length, and the capacity ratio against your applied load.
Worked example
A C-shape weld 8 inches wide by 10 inches tall, with a 1/4-inch E70XX fillet, carries a 50-kip vertical load at a 6-inch eccentricity.
- Total weld length = 8 (bottom) + 10 (side) + 8 (top) = 26 inches.
- Elastic integration of direct plus moment stress gives a controlling unit stress of 0.0742, so C = 1 / (0.0742 × 26) ≈ 0.52.
- Weld strength per inch = 0.75 × 0.6 × 70 × 0.707 × 0.25 = 5.57 kips/in.
- Capacity = 0.52 × 26 × 5.57 = 75.3 kips; capacity ratio = 50 / 75.3 = 0.664.
C ≈ 0.52, total weld length 26 in, required leg ≈ 3/16 in, and capacity ratio ≈ 0.664 — the 1/4-inch weld is adequate.
Frequently asked questions
- What is the weld group coefficient C?
- C relates the applied eccentric load to the stress at the most highly stressed point of the weld. Multiplying C by the total weld length and the per-inch design strength gives the eccentric capacity of the weld group.
- Why is the effective throat 0.707 times the leg size?
- For an equal-leg fillet weld the shortest path across the weld throat is the leg size multiplied by sin(45°) = 0.707. AISC bases fillet weld strength on this effective throat times the weld length.
- Which electrode strength should I use?
- E70XX (Fexx = 70 ksi) is the most common choice for structural steel and matches typical mild steel base metal. The calculator also supports E60XX, E80XX, and E90XX so you can match higher-strength filler metals.
- How is the required weld size determined?
- The tool back-solves the leg size that exactly resists your applied load given the coefficient C and total length, then rounds up to the nearest 1/16 inch since weld sizes are specified in sixteenths.