------------------ | ----------- | ----------- | ----------- | ----------- | | Diameter (in) | 0.500 | 0.625 | 0.750 | 0.875 | | Cross-section area (in²) | 0.196 | 0.307 | 0.442 | 0.601 | | Head diameter (in) | 1.0 | 1.25 | 1.25 | 1.50 | | Head thickness (in) | 5/16 | 5/16 | 3/8 | 3/8 | | Min length after weld | 2.0 | 2.5 | 3.0 | 3.5 | | Common length (in) | 3, 4 | 3, 4, 5 | 3, 4, 5, 6 | 4, 5, 6 | | Fy (ksi) | 51 | 51 | 51 | 51 | | Fu (ksi) | 65 | 65 | 65 | 65 |

The 3/4 inch diameter stud is by far the most commonly used in building construction.

Stud Nominal Strength

Per AISC Equation I3-3:

Qn = min(0.5 × Asc × √(f'c × Ec), Rc × Asc × Fu)

where:

Simplified Stud Capacity (3/4 in, Solid Slab)

f'c (psi) Ec (ksi) Qn per stud (kips) Controlling Mode
3,000 3,320 17.7 Concrete
3,500 3,590 19.5 Concrete
4,000 3,830 21.2 Concrete
4,500 4,070 22.8 Concrete
5,000 4,290 23.5 Steel stud

Note: 3/4 in stud, Asc = 0.442 in², Fu = 65 ksi. Steel limit = 0.5 × 0.442 × 65 = 14.4 kips (with Ω=2.0 for ASD) or Qn = 23.5 kips (nominal, for LRFD: φQn = 17.6 kips).

Stud Capacity Through Metal Deck

When studs are welded through corrugated metal deck, the capacity is reduced:

Deck Orientation Weak Position Strong Position
Strong (ribs perpendicular) 0.70 × Qn 1.0 × Qn
Weak (ribs parallel) 0.90 × Qn 1.0 × Qn

Additional reductions apply when the rib height exceeds the stud length or when the deck flute is narrow. See AISC Table I3-2 for the complete reduction factors.

Number of Studs Required

Full Composite Action

The total horizontal shear force to be transferred equals the lesser of:

Vh = min(0.85 × f'c × Ac, Fy × As)

where Ac = concrete area within effective width, As = steel beam area.

Number of studs for full composite: N = Vh / Qn (per shear span)

Partial Composite Action

When fewer studs are provided, the composite section has reduced capacity:

V'h = N × Qn

The composite moment capacity is calculated based on the actual shear transfer V'h.

Minimum degree of composite action: AISC requires the composite moment capacity to exceed the non-composite moment capacity by at least some amount. In practice, a minimum of 25-50% composite action is typical.

Stud Layout

Spacing Requirements

Requirement Limit
Minimum spacing (along beam) 6 × stud diameter (4.5 in for 3/4 in stud)
Maximum spacing 8 × slab thickness, or 36 in
Minimum transverse spacing 4 × stud diameter (3 in for 3/4 in stud)
Maximum transverse spacing Not specified (practical: within slab effective width)
Studs per rib (metal deck) 1 or 2 per rib typical
Edge distance (stud to slab edge) Not less than stud head diameter

Typical Layout Patterns

For a W21x44 beam spanning 30 ft with 3/4 in studs:

Composite Level Studs per half-span Total studs Approx. capacity increase
Non-composite 0 0 0%
25% 8 16 ~25%
50% 15 30 ~50%
75% 23 46 ~75%
100% 30 60 ~85-100%

Effective Concrete Width

Per AISC Section I3.1a:

be = min(b/2, L/8) on each side of beam centerline

where b = beam spacing, L = beam span.

Beam Spacing (ft) Span (ft) Effective Width (in)
4 20 48 (controlled by b/2)
5 25 60 (controlled by b/2)
6 30 72 (controlled by b/2)
8 30 90 (controlled by L/8)
10 30 90 (controlled by L/8)

Frequently Asked Questions

What size shear studs are used in composite beams? 3/4 inch diameter is the most common. 5/8 inch is used for lighter beams and deck profiles. 7/8 inch is used for heavy bridge girders. Studs are typically 3-5 inches long.

How many shear studs do I need? For full composite action, the number is determined by dividing the total horizontal shear (Vh) by the capacity per stud (Qn). For a W21x44 spanning 30 ft with 4 ksi concrete, approximately 30 studs per half-span (60 total) are needed for full composite action.

Can I have too many studs? Yes. Beyond full composite action, additional studs do not increase capacity. They add cost and weld time without benefit. The number should be limited to that required for full composite action, or a specified partial composite level.

Do I need studs on both sides of the beam? Studs are typically placed on both sides of the beam top flange, but this is for symmetry and constructability, not a code requirement. Single-row studs are acceptable if the capacity works out.

How are studs installed? Studs are welded to the top flange using a stud welding gun (arc welding with a ferrule ceramic). The process takes 1-2 seconds per stud. Studs can be welded through metal deck (with proper ferrules and procedure).

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Disclaimer

This is a calculation tool, not a substitute for professional engineering certification. All results must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs. [object Object]

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.

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