When to use: Determine the design shear strength of a fillet weld per AISC 360-16 §J2.4 (LRFD). The strength depends on the electrode classification FEXX, the weld leg size w (which sets the effective throat te = 0.707·w), and the total weld length L. Compare the design capacity φRn against the required shear Ru to verify the joint.
Calculate the LRFD design shear strength of fillet welds per AISC 360-16 Section J2.4. Enter electrode classification (FEXX), weld leg size w, and total weld length L to compute effective throat te, nominal strength per inch, total design capacity phiRn, and check against the required shear Ru.
The effective throat of a fillet weld is te = 0.707·w (perpendicular distance from root to face for a 45° weld). The nominal weld shear stress is Fnw = 0.6·FEXX and the design strength per unit length is φrn = 0.75·Fnw·te = 0.75·0.6·FEXX·0.707·w kip/in. Total design strength φRn = φrn·L. Compare φRn ≥ Ru to verify the weld.
Effective throat: te = 0.707·w. Weld shear strength: Fnw = 0.6·FEXX. Design strength per inch: φrn = 0.75·0.6·FEXX·0.707·w. Total design strength: φRn = φrn·L. For E70XX electrode: φrn = 0.75·0.6·70·0.707·w = 22.27·w kip/in. Minimum fillet weld size per AISC Table J2.4 varies from 3/16 in to 5/16 in depending on base metal thickness.
Use for any steel connection using fillet welds including beam-to-column shear tabs, bracket plates, base plates, gusset plates, and stiffener welds. This formula applies to welds loaded in-plane (shear parallel to weld axis) or at 0° to the weld axis. For welds loaded at angle θ to the weld axis, the directional strength increase factor (1 + 0.5·sin^1.5θ) per AISC §J2.4b can increase capacity up to 50% for transverse loading.
The most common electrode in structural steel fabrication is E70XX (FEXX = 70 ksi), matching A36 and A992 base metals. E60XX is used for lower-strength steels. E80XX and higher are used for high-strength steels. The electrode strength must meet or exceed the base metal tensile strength (Fu).
AISC Table J2.4 specifies minimum fillet weld sizes based on the thicker connected part: 1/8 in for parts up to 1/4 in thick, 3/16 in for 1/4–1/2 in, 1/4 in for 1/2–3/4 in, 5/16 in for parts over 3/4 in thick. Also, the weld leg size must not exceed the plate thickness minus 1/16 in for plates 1/4 in or thicker.
For material less than 1/4 in thick, maximum weld size equals the base metal thickness. For material 1/4 in or thicker, maximum weld size is material thickness minus 1/16 in, to avoid burning through the base metal edge.
No — this formula is specifically for fillet welds (J2.4). Complete joint penetration (CJP) groove welds have strength equal to the base metal (φ = 1.0 in tension). Partial joint penetration (PJP) groove welds have their own strength equations based on effective weld throat per AISC §J2.1.