Welded Connections Calculator

Fillet-weld group screening for segmented weld geometry and in-plane loading. The module accepts weld size, electrode strength, base-metal strength, and load components Vx, Vy, N, and Mz, then reports the governing weld capacity and capacity per millimetre.

Engineering Scope

This calculator evaluates fillet-weld capacity from the entered geometry and load state, then compares the demand with the governing weld resistance for the selected code routine. The result set exposes the total capacity, capacity per millimetre, and the governing utilization.

The current scope is fillet weld only. Groove welds, out-of-plane loading, fatigue, and fracture-critical checks are outside the module.

Calculation Model

For equal-leg fillet welds the effective throat is taken as:

te = w / sqrt(2)
phiRn = 0.75 * 0.6 * FEXX * te * L

The module accepts a segmented weld geometry, electrode classification, base-metal Fu, base-plate thickness, and in-plane loads Vx, Vy, N, and Mz. The calculation trace reports the selected code reference and the governing capacity values used in the result.

Outputs

The page reports total weld capacity, capacity per millimetre, and the governing utilization ratio for the selected load state. Use the trace to reproduce the governing check independently.

Limitations

• The page is limited to fillet welds.
• The weld group is evaluated as a planar in-plane problem only.
• Groove welds, out-of-plane loading, fatigue, and fracture toughness checks are not included.
• All calculations and outputs must be independently verified by a licensed Professional Engineer before design use.

Worked Example

For the default 300 mm rectangular fillet-weld group with 8 mm E70XX electrode and combined in-plane loading, the module calculates a total capacity and a capacity per millimetre from the segmented geometry, then reports the governing utilization. Use the trace to reproduce the governing check independently.

Fillet Weld Design — AISC 360 Chapter J

Fillet welds are the most common welded connection in structural steel. They transfer force through shear on the effective throat, which is the shortest distance from the root to the face of the weld.

Effective throat

The effective throat of an equal-leg 45-degree fillet weld is 0.707 times the leg size (w). For other dihedral angles, the effective throat equals w times cos(theta/2).

Fillet weld strength per AISC J2.4

The design strength of a fillet weld is:

phi x Rn = phi x 0.6 x F_EXX x t_e x L_w

Where phi = 0.75, F_EXX is the electrode tensile strength (typically 70 ksi for E70XX), t_e is the effective throat in inches, and L_w is the effective weld length in inches.

For E70XX with equal-leg fillet: phi x Rn per inch = 0.75 x 0.6 x 70 x 0.707 x w = 22.3w kips/in For w = 5/16 in: phi x Rn = 6.96 kips/in For w = 1/4 in: phi x Rn = 5.57 kips/in

Minimum and maximum fillet weld sizes

Maximum weld size along edges: 1/16 inch less than material thickness for material under 1/4 inch thick; equal to thickness for material 1/4 inch or thicker.

Common weld joint types

Worked example — single-plate shear connection

Given: W16x36 beam to W12x65 column. Reaction Vu = 45 kips (LRFD factored). Single plate: 3/8 inch thick, A36 steel (Fy = 36 ksi). Weld each side of plate to column flange. Use E70XX electrodes, 5/16 inch fillet weld.

Required weld length each side: phi x Rn per inch = 22.3 x 5/16 = 6.97 kips/in Lw = Vu / (2 x phi x Rn) = 45 / (2 x 6.97) = 3.23 in each side

Use Lw = 4 in minimum (practical minimum) Capacity = 2 x 4 x 6.97 = 55.7 kips > 45 kips → OK

Groove Welds — Complete and Partial Joint Penetration

Complete joint penetration (CJP)

CJP groove welds develop the full strength of the connected material. They require back-gouging or welding from both sides and are used where the highest strength is needed: column splices, moment connections, and critical joints.

For CJP welds per AISC J2.1: the weld strength equals the base metal strength. The design does not check the weld itself but rather the base metal on each side.

Partial joint penetration (PIP)

PIP groove welds have a defined effective throat that is less than the material thickness. They are used for non-critical connections, column splices in compression-only members, and where full-penetration welding is impractical.

PIP effective throat equals the groove depth minus 1/8 inch for SMAW and GMAW processes.

Weld Symbol Basics

AWS A2.4 welding symbols communicate joint design on engineering drawings. The basic symbol has a reference line, arrow, and tail. The arrow points to the joint, weld symbols on the arrow side go below the reference line, and other-side welds go above.

Common symbols: fillet (triangle), plug/slot (rectangle in arrow), bevel groove (single bevel), V-groove, J-groove, U-groove. Supplementary symbols include weld-all-around (circle at junction), field weld (flag), and contour (flush or convex).

Fillet Weld Capacity Table — E70XX Electrode

The table below provides the design strength per linear inch for common fillet weld sizes using E70XX electrodes (F_EXX = 70 ksi). Values are for equal-leg fillet welds with the effective throat = 0.707w.

Formula: phi x Rn per inch = 0.75 x 0.6 x 70 x 0.707 x w = 22.3w kips/in

Base metal shear strength comparison

The weld must also not exceed the base metal shear capacity. For A572 Gr 50 (Fu = 65 ksi) base metal:

Base metal shear per inch (AISC J4.2):
  phi x Rn = 0.75 x 0.6 x Fu x t = 0.75 x 0.6 x 65 x t = 29.25t kips/in

For 3/8" plate: 29.25 x 0.375 = 10.97 kips/in
For 1/2" plate: 29.25 x 0.50 = 14.63 kips/in
For 3/4" plate: 29.25 x 0.75 = 21.94 kips/in

The governing capacity is the lesser of weld strength and base metal shear strength.

Multi-Code Fillet Weld Strength Comparison

Different steel design codes use different formulations for fillet weld capacity. The table below compares the design strength for a 5/16 inch fillet weld on 1/2 inch plate with E70XX / G350 / E49XX electrodes.

The AISC formulation generally gives the highest capacity for equivalent weld sizes because it uses the electrode tensile strength directly without additional reduction factors for mismatch between weld and base metal.

Weld Group Analysis — Eccentric Loading

When the applied load does not pass through the centroid of the weld group, the welds must resist both direct shear and torsional shear. The elastic method (AISC Steel Manual Part 7) distributes the torsional shear based on polar moment of inertia.

Elastic method for weld groups

Direct shear (uniform): r_ix = Px / (sum of L_w)
                         r_iy = Py / (sum of L_w)

Torsional shear: r_tx = T x y_bar / J_p
                  r_ty = T x x_bar / J_p

Where:
  T = P x e (torque from eccentricity)
  J_p = I_x + I_y (polar moment of inertia of weld group)
  x_bar, y_bar = distance from centroid to weld segment

Resultant: r_i = sqrt((r_ix + r_tx)^2 + (r_iy + r_ty)^2)
Governing point is typically the farthest weld segment from centroid

Instantaneous center of rotation method

The AISC Steel Manual also provides the instantaneous center (IC) method tables for common weld group configurations (single angle, double angle, single plate). The IC method accounts for the non-linear deformation of welds at different stress levels and generally gives higher capacities than the elastic method. It is the preferred method for final design, while the elastic method is used for preliminary checks and where the IC tables do not cover the specific geometry.

Weld Inspection and Quality Control

Visual inspection (VT)

All welds require visual inspection per AWS D1.1. The inspector checks for:

• Correct weld size (use weld gauge)
• Undercut (maximum 1/32 inch for structures)
• Porosity (surface)
• Cracks (none permitted)
• Profile (convex or flush as specified)
• Overlap (not permitted)

Non-destructive testing (NDT)

AISC 360 Chapter N specifies the inspection requirements based on the structural system and seismic design category. For most building structures, visual inspection is sufficient for fillet welds, while CJP welds in seismic force-resisting systems require UT or MT.

Welding Process Selection

For structural steel connections in buildings, FCAW is the most common shop process (high deposition rate, good penetration) and SMAW or FCAW are used for field welds. GMAW is gaining popularity for lighter connections but requires wind protection for outdoor use.

Electrode Selection Guide

E7018 is the standard low-hydrogen electrode for structural steel construction. Low-hydrogen electrodes are required for A514 and A572 Gr 60+ steels, for restrained joints, and wherever hydrogen-induced cracking is a concern.

Frequently Asked Questions

What is the difference between E70XX and E80XX electrodes? E70XX electrodes have a minimum tensile strength of 70 ksi (483 MPa), while E80XX electrodes have 80 ksi (552 MPa). The electrode should match or slightly exceed the base metal strength. For A992 steel (Fu = 65 ksi), E70XX is appropriate. For higher-strength steels like A514 (Fu = 110-130 ksi), E110XX electrodes are used.

Can I use a larger fillet weld to compensate for a shorter weld length? Yes, within limits. The weld capacity is proportional to the effective throat (0.707w) times the length. Increasing the weld size from 1/4 to 5/16 inch increases capacity by 25%. However, AISC limits the maximum fillet weld size along edges and the minimum length to not less than 4 times the weld size.

What is the minimum effective length of a fillet weld? AISC J2.2b requires that the effective length of a fillet weld be at least 4 times the nominal weld size. For a 5/16 inch fillet, the minimum length is 4 x 5/16 = 1.25 inches. In practice, most structural fillet welds are at least 2-3 inches long to accommodate start/stop effects.

Does weld position affect strength? The weld position (flat, horizontal, vertical, overhead) does not affect the design strength calculation in AISC. However, vertical and overhead positions are harder to execute and may produce lower-quality welds with more defects, which is why some specifications require a higher level of inspection for out-of-position welds.

Run This Calculation

• Welded Connections Calculator — fillet weld capacity for in-plane loading with AISC 360, AS 4100, EN 1993, and CSA S16.
• Minimum Fillet Weld Size Reference — AISC Table J2.4 minimum sizes by base metal thickness.
• Fillet Weld Size Chart — complete fillet weld capacity tables.

Related Pages

• Bolted connections calculator
• Base plate and anchor design calculator
• Weld symbol chart
• Steel grade reference
• How to verify calculator results

Verification

Confirm the weld size, electrode classification, segment geometry, base-metal strength, and active code edition before relying on the result. Replicate the governing capacity independently by hand or in a spreadsheet.

Related Pages

• Minimum fillet weld size
• Steel grade reference
• Bolted connections calculator
• Base plate and anchor design calculator
• How to verify calculator results

Disclaimer

All calculations and reported values must be independently verified by a licensed Professional Engineer before use in design, detailing, procurement, fabrication, construction, or permit submission. This tool is provided without warranty of accuracy, completeness, fitness for purpose, or project-specific code compliance. The site operator disclaims liability for any loss, damage, claim, cost, or consequence arising from use of, or reliance on, the calculator or its outputs.