Weld Stud Load Capacities & Engineering Reference

This page provides engineering reference data for headed concrete anchor (HCA) weld studs and shear connectors per AWS D1.1 and AISC 360. All values are nominal design strengths -- apply applicable resistance factors (φ) or safety factors (Ω) per your project's design basis (LRFD or ASD). See the disclaimer at the bottom of this page before using any values in design calculations.

Weld Stud Mechanical Property Requirements (AWS D1.1)

AWS D1.1 Section 7 specifies the minimum mechanical properties that stud base material and completed welds must meet. These requirements apply to all headed concrete anchor and shear connector weld studs.

Shear Connector Capacity in Solid-Slab Construction (AISC 360)

For shear connectors welded directly to a steel beam flange (no metal deck), nominal shear strength Q_n is governed by AISC 360 Equation I8-1. The lesser of the two expressions controls:

Q_n = 0.5 × A_sa × √(f'_c × E_c) ≤ R_g × R_p × A_sa × F_u

Where A_sa = shank cross-sectional area (in²), f'_c = concrete compressive strength (ksi), E_c = concrete modulus of elasticity (ksi), F_u = minimum tensile strength of stud (ksi), and R_g, R_p = deck geometry reduction factors.

*Fracture limit governs for larger diameters at higher concrete strengths. Actual Q_n = lesser of concrete breakout and stud fracture expressions. R_g=1.0, R_p=0.75 for solid slab (no deck). Normal-weight concrete assumed (w_c=145 pcf, E_c=33w_c^1.5√f'_c).

Shear Connector Capacity with Metal Deck (AISC 360)

When shear connectors are welded through metal deck, the nominal shear strength is reduced by geometry factors R_g and R_p from AISC 360 Table C-I8.2a. The reduction depends on whether deck ribs run parallel or perpendicular to the steel beam.

"Strong position" = stud centered in the deck rib closest to the midspan of the rib. R_p = 0.75 applies to most conditions; 0.625 applies to studs in the "weak" position in deck ribs (stud not in the strong rib position). Confirm with AISC 360 Table C-I8.2a for your specific deck geometry and stud placement.

Effective Q_n by Diameter -- Composite Deck (Perpendicular Ribs, 1 Stud per Rib)

The table below shows the reduced effective design strength for 3/4" through 1" shear connectors in the most common composite deck scenario -- deck ribs perpendicular to the steel beam, one stud per rib. This is the governing condition for most composite floor beams.

*AISC 360 caps Q_n at 0.5A_saF_u = 21.0 kips for 3/4" and larger studs (stud fracture governs at f'c=4ksi). This is why 3/4" is the practical maximum effective shear connector diameter for composite deck -- larger diameters add weight and cost without increasing the design capacity per stud.

Minimum Stud Spacing Requirements (AWS D1.1 and AISC 360)

AWS D1.1 Production Weld Qualification Tests

AWS D1.1 requires production weld testing at the start of each shift or when welding conditions change. Studs that fail production testing require the weld to be condemned and the area retested. Common production tests:

• Bend test (ring test): Studs 5/8" diameter and smaller are bent 15 degrees from vertical using a pipe or ring. Studs 3/4" and larger are bent 30 degrees. No cracks in the weld or base metal -- test passes.
• Torque test: A wrench applies a specified torque to the stud. Used for studs in congested areas where bend testing is not practical. Torque values are per the equipment manufacturer's WPS.
• Tension test: Pull-out test to a specified tensile load. Less common in field testing; used for qualification of new procedures.

AWS D1.1 Section 7.8 requires testing of the first two studs welded each shift. If either fails, two additional studs in that area are tested. If either of those fails, all studs welded since the last passing test are condemned and the weld procedure is reviewed.

Tension Capacity: ACI 318 Concrete Breakout (HCA Applications)

For headed anchor studs in tension (ACI 318 Chapter 17), the concrete breakout capacity N_cb is calculated using the Concrete Capacity Design (CCD) method. The basic breakout capacity depends on embedment depth h_ef, concrete strength f'_c, and modification factors for edge distance, group effects, and eccentricity.

The basic single-anchor breakout strength in tension (from ACI 318-19 Eq. 17.6.2.1a):

N_cb = (A_Nc / A_Nco) × ψ_ed,N × ψ_c,N × ψ_cp,N × N_b

Where N_b = k_c × λ × √f'_c × h_ef^1.5 (k_c = 17 for cast-in anchors, 10 for post-installed).

N_b values assume cast-in headed anchor (k_c=17), normal-weight concrete (λ=1.0), single anchor far from edges (A_Nc/A_Nco=1.0, all ψ factors = 1.0). Actual project capacity will be lower for edge conditions, groups of anchors, and eccentricity. These are maximum theoretical single-anchor breakout strengths only.

Related Resources

• Weld Stud Selection Guide -- all stud types, process selection, materials overview
• Headed Concrete Anchors and Shear Connectors Selection Guide -- diameter selection, embedment, composite deck guidance
• Deformed Bar Anchors Selection Guide -- precast and tilt-up concrete applications
• Threaded Weld Studs Selection Guide -- pitch diameter, full thread, and collar stud types
• Weld Stud Ferrule Sizing Chart -- matched ferrule part numbers by diameter
• Nelson Weld Stud Cross-Reference -- Cox Industries and Bluearc equivalents for Nelson H4L studs

Frequently Asked Questions

What resistance factor should I use for shear connectors in LRFD design?

Per AISC 360 Commentary, the resistance factor φ = 0.65 applies to the nominal shear strength Q_n of headed stud shear connectors. For ASD, the safety factor Ω = 2.31. Apply the appropriate factor based on your project's design basis.

Why does shear connector capacity not increase proportionally with stud diameter above 3/4"?

For larger studs at typical concrete strengths, the stud fracture limit (R_gR_pA_saF_u) governs rather than the concrete limit. Above 3/4", the concrete can develop more force than the stud can carry, so increasing diameter just adds material without adding capacity. The 3/4" stud is at the practical optimum for composite deck construction.

What is the minimum embedment depth for a cast-in headed anchor per ACI 318?

ACI 318-19 Section 17.5.3.1 requires a minimum effective embedment h_ef of at least 1.5 times the head diameter, but not less than 5 stud diameters (5d). For a 1/2" stud with a 7/8" head: min h_ef = max(1.5 x 0.875, 5 x 0.5) = max(1.31", 2.5") = 2.5". Most designs use 8d or more for full breakout capacity.

Do stainless steel weld studs have higher load capacity than carbon steel?

Stainless studs have higher tensile strength (75 ksi vs. 65 ksi for A108), which increases the stud fracture limit slightly. However, stainless studs are not recognized in AISC 360 Chapter I or AWS D1.1 Annex A for use as shear connectors without separate qualification testing. For HCA applications, a licensed engineer must verify that the stainless WPS and material certification meet applicable code requirements.

What is the difference between Q_n and φQ_n?

Q_n is the nominal (unfactored) design shear strength from AISC 360 Equation I8-1. φQ_n is the design strength in LRFD, with φ = 0.65. For ASD, the allowable strength is Q_n/Ω where Ω = 2.31. Always confirm which basis (LRFD or ASD) your structural engineer is using before applying values from this page.