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Weld Strength Calculator

Calculate the design strength of fillet and butt welds based on throat thickness, electrode grade, and weld length.

Project Specifications
Weld Geometry
Leg length of fillet weld
Material & Workshop
Safety Settings
Technical data
Throat Thickness ($t_t$): 0 mm
Capacity per mm: 0 kN/mm
Total Mass Eq: 0 kg
Calculated Output
Weld Capacity ($P_{dw}$)
0 kN
0 kN
Design Capacity
Shear Failure
Limit State
Comprehensive Guide

Structural Welding and Throat Physics

Understand the molecular bond. Learn why 'Fillet Welds' are designed for shear and why 'Field Welds' require a 20% higher safety factor than shop welds.

The Seamless Connection

Unlike bolts, which rely on holes and bearing pressure, welding creates a continuous molecular bond between two pieces of steel. In structural engineering, the most common type is the Fillet Weld (a triangular bead in the corner of two plates). Interestingly, a fillet weld is always assumed to fail in **Shear** at its weakest point: the Throat Thickness.

Fillet Weld Equation (IS 800)

$$f_{wd} = \frac{f_u}{\sqrt{3} \gamma_{mw}}$$ $$P_{dw} = L_w \times t_t \times f_{wd}$$ $$t_t = 0.7 \times s \text{ (for 90° joints)}$$

Workshop vs. Field Welds

  • Shop Welds ($\gamma_{mw} = 1.25$): Performed in a controlled environment with proper lighting, positioning, and inspection. These are considered highly reliable.
  • Field Welds ($\gamma_{mw} = 1.50$): Performed on the construction site, often at heights, in wind/rain, or in awkward positions. Because the quality is harder to control, we apply a **$20\%$ penalty** to their design strength.

The Throat Thickness Theory

If you have a $6$mm weld (leg length $s$), the distance from the corner to the face of the weld (the throat $t_t$) is only about $4.2$mm. Even though the weld looks $6$mm thick, it is the $4.2$mm "internal" thickness that actually resists the load. This is the single most important concept in weld design.

Frequently Asked Questions (FAQ)

What is a 'Full Penetration' weld?

In a Full Penetration Butt Weld, the weld metal fills the entire thickness of the joint. In this case, the weld is often **Stronger** than the plates themselves. For design, we simply use the strength of the parent plate, assuming the weld will never be the point of failure.