Fillet Weld Torsion Size Calculator

Calculator Inputs

Weld layout

Length unit

Stress unit

Weld group width

Weld group height

Applied torque

Torque unit

Direct shear force

Force unit

Force eccentricity

Direct shear angle, degrees

Allowable method

Manual allowable shear stress

Electrode tensile strength

Safety factor divisor

Weld efficiency factor

Throat factor

Trial fillet leg size

Rounding increment

Example Data Table

Input	Example Value	Meaning
Weld layout	Closed rectangular group	Four weld sides around a plate bracket
Width and height	200 mm by 150 mm	Centerline dimensions of the weld group
Applied torque	8,000,000 N-mm	Known twisting moment on the weld group
Direct shear and eccentricity	18,000 N and 50 mm	Extra moment is added as V × e
Allowable shear stress	110 MPa	Entered design limit for weld throat stress
Typical output	About 2.3 mm required leg	Rounded result depends on selected increment

Formula Used

Total torsion: Ttotal = T + V × e
Effective throat: a = throat factor × fillet leg size
Direct shear stress: τd = V ÷ (a × L)
Weld group polar line moment: Jw = ∫ r² dl
Torsional shear flow numerator: qt = Ttotal × r ÷ Jw
Combined demand: qmax = maximum vector sum of direct and torsional shear flow
Required throat: areq = qmax ÷ allowable shear stress
Required leg: sreq = areq ÷ throat factor

This is an engineering screening tool. Always compare results with the governing welding standard, base metal capacity, inspection requirements, and project specifications.

How To Use This Calculator

Select the weld group layout that matches the connection.
Choose length and stress units before entering values.
Enter weld group width and height along the weld centerlines.
Enter applied torque, direct shear, and eccentricity.
Set the load angle for the direct shear direction.
Choose manual allowable stress or electrode strength estimate.
Enter throat factor, trial leg size, and rounding increment.
Press the calculate button and review the controlling result.
Download the CSV or PDF report from the result panel.

Fillet Weld Torsion Guide

Fillet weld groups often carry torque and shear together. A bracket, plate, lug, or short arm may twist the weld group. The load does not spread evenly. Points far from the weld group centroid receive greater torsional demand. This calculator turns that idea into a clear sizing check.

What The Calculator Evaluates

The tool treats each weld side as a line element. It finds total weld length, group centroid, and polar line moment. Direct shear is spread across the total effective throat area. Torsional shear is based on distance from the centroid. The tool then combines both shear vectors at many points. The highest combined stress controls the required throat size.

Why Throat Size Matters

A fillet weld leg is not the same as its throat. For a standard equal leg fillet weld, effective throat is about 0.707 times the leg. The throat carries the calculated shear. The calculator converts required throat into required leg size. It can also round the answer to a selected shop increment. This helps match common fabrication practice.

Advanced Inputs

Use torque when a twisting moment is already known. Use direct shear when the weld group also supports a force. Add eccentricity when the force acts away from the weld centroid. The calculator adds that eccentric moment to the applied torque. A load angle lets you rotate the direct shear direction. This is useful for vertical, horizontal, or inclined loads.

Interpreting Results

A utilization near 100 percent means the selected weld is near its limit. A lower value gives more reserve. The critical point shows where the combined shear is largest. The result is a screening calculation. Final design must follow the governing code, material limits, weld process, inspection class, and engineer approval.

Good Practice Notes

Keep units consistent. Check base metal thickness before selecting a large weld. Very large fillet welds may not improve strength if the connected plate controls. Consider fatigue, impact, distortion, access, and weld return details. For important structures, compare results with your design standard. Also review the documented welding procedure.

Document assumptions with each printout. Record electrode class, safety factor, dimensions, torque source, and rounding rule. Clear records make review easier when loads change during coordination.

FAQs

What does fillet weld torsion mean?

It means the weld group resists a twisting moment. The twist creates higher shear at points farther from the weld group centroid.

What is effective throat size?

Effective throat is the shortest resisting distance through the weld. For equal leg fillet welds, it is commonly estimated as 0.707 times the leg.

Why does eccentricity matter?

Eccentricity creates extra torsion. The calculator adds V × e to the entered applied torque, so the weld group receives a higher combined demand.

Can I use inch and ksi units?

Yes. Select inches for length and ksi for stress. The calculator converts internally, then reports final values in the selected units.

What is Jw in the result?

Jw is the polar line moment of the weld group. It measures how the weld line is distributed around its centroid.

Does this replace a welding code check?

No. It is a sizing aid. Final weld design must follow the project code, material strength, base metal checks, and inspection requirements.

Why is the critical point shown?

The critical point is where the combined shear flow is largest. That location controls the required throat and leg size.

What if utilization is above 100 percent?

The trial weld is overstressed for the entered assumptions. Increase leg size, improve the layout, reduce load, or review allowable stress.