Weld joint type
T-Joint
A T-joint sets one member perpendicular to the face of another, and it is normally filleted on both sides — the most common joint in structural fabrication.
Geometry and preparation
| Configuration | One member meeting the face of another at approximately 90 degrees, away from its edge. |
|---|---|
| Edge preparation | None for fillet welds. Full-penetration T-joints require a single or double bevel or J groove on the upright member. |
| Strength | Fillet capacity is governed by the throat, which for an equal-leg fillet is the leg size multiplied by 0.707. Doubling the leg size does not double the strength economically — two smaller fillets usually beat one large one. |
Characteristics
- The workhorse joint of structural steel: beams to columns, stiffeners to webs, brackets to plates.
- Double fillets are standard because a single fillet bends the joint under load.
- Full penetration requires bevelling the upright member, usually shown as a bevel-groove or J-groove symbol combined with a fillet.
- Puts through-thickness stress on the horizontal member, which raises the risk of lamellar tearing on thick plate.
- Fillet size is often overspecified: a 5/16 in fillet contains more than twice the metal of a 3/16 in fillet.
Weld types used on a t-joint
Where it is used
- Structural steel connections and stiffeners
- Machine bases and frames
- Tank and vessel nozzles and supports
- Handrails, brackets and general fabrication
T-Joint — common questions
What size fillet weld does a T-joint need?
It depends on the load and the governing code, but a common practical minimum is a fillet leg roughly equal to the thickness of the thinner member, up to the code's maximum. Oversizing wastes filler and adds distortion without proportional strength.
What is the throat of a fillet weld?
The shortest distance from the root to the face of the weld — for an equal-leg fillet, the leg size multiplied by 0.707. The throat, not the leg, is what carries the load.
When does a T-joint need a groove weld?
When the design calls for complete joint penetration. The upright member is bevelled into a single or double bevel or J groove, and the symbol usually combines the groove with a fillet to give the finished weld its contour.
What is lamellar tearing?
A crack that runs parallel to the surface of the base plate, caused by weld shrinkage pulling on the plate through its thickness. It is a risk on thick T-joints with large welds, and is addressed with lower-strength filler, buttering layers and plate specified for through-thickness properties.
Other joint types
Butt Joint
A butt joint places two members edge to edge in the same plane — the simplest joint to draw and the one that most…
Lap Joint
A lap joint overlaps two members and welds along the exposed edges — no edge preparation, forgiving fit-up, and the…
Corner Joint
A corner joint brings two members together at their edges to form an L, and unlike a T-joint the upright lands on the…
Edge Joint
An edge joint lays two members face to face and welds along their common edge — a light-duty joint used to join…