SkyCiv Welded Connection Design

Bolting and riveting clamp components together. Welding fuses them, which is why welded joints carry high loads, transfer force without a step change in stiffness, and leave more freedom on geometry.

High-rise steel buildings, highway bridges, pressure vessels and offshore platforms all depend on them.

A permanent structural joint made by heating two or more metal components to melting point, usually with a filler metal added, so they cool as one continuous piece.

A mechanical joint depends on fasteners and hole tolerances. A weld fuses the base metals directly instead, which is where its rigidity, its joint efficiency and its clean appearance come from.

Classified by weld geometry and joint configuration:

• Fillet welds: used in lap, tee and corner joints, joining surfaces positioned roughly perpendicular to one another. Load transfer is checked as shear across the theoretical throat area.
• Groove (butt) welds: between members in the same plane, or in perpendicular configurations needing full strength. Complete joint penetration (CJP) grooves develop the full strength of the base metal, and partial joint penetration (PJP) grooves cover lower load requirements.
• Plug and slot welds: weld metal deposited into circular or elongated holes in one of two overlapping plates, to prevent local buckling or transmit shear across a wide contact area.

Fillet welds do most of the work in ordinary steelwork. A CJP groove takes more edge preparation and more inspection, and it gets specified where the joint has to be as strong as the member it joins.

A safe design has to cover structural failure and metallurgical failure:

1. Shear failure of the weld throat: the primary mode for fillet welds, when the applied force exceeds shear capacity on the effective throat plane.
2. Base metal tension or shear failure: the connected plate yields or ruptures next to the weld boundary under excessive stress.
3. Heat-affected zone cracking: material degradation or hydrogen-assisted cracking in the base metal near the weld, caused by the rapid thermal cycles of welding.
4. Lamellar tearing: separation within thick plate beneath a weld, driven by restraint stresses through the thickness as the weld metal shrinks.
5. Fatigue failure: cyclic loading concentrates stress at weld toes and internal discontinuities, and cracks initiate and propagate from there.

The first two are calculations. The last three are settled at the fabrication stage, by detailing, preheat and inspection, which is why the design and the welding procedure need to be settled together.

Designing to AISC 360-16 or AS 4100:2020 means calculating weld throat areas, directional strength factors and eccentricities precisely. SkyCiv automates those checks:

• Model 3D welded joint details in a web browser, from a library of over 80 pre-configured AISC connection types.
• Evaluate fillet weld group capacities under combined shear, tension and moment.
• Analyse weld group properties by the elastic and the instantaneous centre of rotation methods.
• Export step-by-step calculation reports with the full formula breakdown, for engineering submittals and code compliance.
• Issue CloudCAD detail drawings with weld callouts and dimensions, and export the geometry to IFC for BIM coordination.

Both weld group methods are there because an eccentrically loaded group can be checked either way, and the instantaneous centre method is the more laborious of the two by hand.

What a welded joint buys you:

• Efficiency and rigidity: continuous material paths, which suits moment-resisting frames and spreads stress without connection plates or bolt holes.
• Material economy: no gusset plates, splice plates or fasteners, so the structural steel weight comes down.
• Appearance: smooth, uninterrupted joints, preferred in architecturally exposed structural steelwork.
• Sealing: continuous welds are airtight and watertight, which matters for storage tanks, pipes and marine structures.

None of that survives poor execution. Welder qualification, edge preparation, preheat protocols and non-destructive testing, whether ultrasonic, radiographic or magnetic particle, are what keep internal flaws out of the joint over its design life.

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