--------- | ----------- | ------------------- | ----------------------- | -------------------------- | | 1.5WR | 1-1/2 | 6 | 4 to 8 | Lowest (tightest profile) | | 2WR | 2 | 6 | 6 to 12 | Moderate | | 3WR | 3 | 6 | 10 to 20 | High (deepest profile) |

The WR suffix denotes "wide rib." Narrow rib (NR) profiles exist but are less common in composite construction because the narrower flute makes shear stud placement more constrained. Always verify the minimum flute width at the top for your specified stud diameter — AISC 360 Section I3.2c requires the stud diameter not exceed 2.5 times the deck flange thickness for studs welded through the deck.

Vulcraft Composite Deck Profiles

Vulcraft, a division of Nucor, supplies approximately 60% of US steel deck. Their composite deck product line uses VLI and VL designations with the 6 in. rib pitch standard.

1.5VLI (1-1/2 in. Deep, Type WR)

The 1.5VLI is the economy option for short-span conditions (4 to 8 ft). It minimizes concrete volume but limits unshored span capability.

Common application: Residential and light commercial floors with 5 to 7 ft beam spacing. The 1.5VLI at 20 gage handles the typical 45 psf construction live load at 6 ft spans.

2VLI (2 in. Deep, Type WR)

The 2VLI is the workhorse for office and institutional floors. It balances span capability, concrete volume, and fire rating.

Common application: Office buildings with 8 to 10 ft beam spacing. The 2VLI at 20 gage handles 50 psf construction live load at 8 ft without shoring and supports 3-1/4 in. lightweight concrete (110 pcf) to achieve a 2-hour fire rating when combined with appropriate reinforcement.

3VLI (3 in. Deep, Type WR)

The 3VLI targets long-span conditions (over 12 ft) where minimizing the number of beams and girders provides floor layout flexibility. The deeper profile adds significant stiffness.

Common application: Office buildings with 12 to 15 ft beam spacing, parking structures, and high-bay industrial floors. The 3VLI at 18 gage handles 50 psf construction live load at 12 ft without shoring.

Verco Deck Profiles

Verco (now part of Nucor via the Verco Decking division) offers the W2 and W3 FormLok profiles featuring a unique trapezoidal rib with embossments that provide mechanical interlock with the concrete slab. This interlock enhances composite action beyond what chemical bond alone provides.

W2 FormLok (2 in. Deep)

W3 FormLok (3 in. Deep)

FormLok advantage: The embossed rib pattern provides horizontal shear transfer capacity (per SDI test data) that exceeds the AISC 360 Section I3.2c calculated values for plain deck. This can reduce the number of shear studs required for full composite action. Always use the manufacturer's published shear transfer values (from ICC-ES evaluation reports) rather than the generic AISC formulas when specifying FormLok.

Gage Selection Guidelines

Steel deck gage follows the Manufacturers' Standard Gage for uncoated sheet steel. The SDI Diaphragm Design Manual, 4th Edition provides section properties for each gage and profile combination.

Heavier Gage Uses

• 16 and 14 gage: High diaphragm shear demands (over 400 plf), concentrated loads from partitions or equipment, and construction loads exceeding 50 psf
• 18 gage: Typical office and commercial floors with 8 to 12 ft spans. The default for most projects
• 20 gage: Residential and light commercial where spans are 6 to 8 ft and loads are moderate
• 22 gage: Roof deck only — not recommended for composite floor deck where shear studs are welded through the deck, because the thin material may burn through during stud welding

Minimum Thickness for Shear Stud Welding

Per AWS D1.1 and AISC 360 Section I3.2c, the deck thickness must be sufficient to support through-deck stud welding without burn-through:

• Minimum deck thickness for 3/4 in. dia. studs: 0.028 in. (22 gage)
• Practical minimum for reliable welding: 20 gage (0.0358 in.)
• For studs 7/8 in. diameter and larger: 18 gage minimum recommended

Construction Loads on Unshored Deck

Per AISC 360 Section I3.2c and SDI, the bare steel deck (before concrete placement) must support:

1. Dead load: Deck self-weight + wet concrete weight (typically 145 pcf normal weight or 110 pcf lightweight)
2. Construction live load: 20 psf uniform OR 150 lb concentrated over a 1 ft square area per OSHA 1926 Subpart R

The deck is typically analyzed as a continuous beam over the supporting steel with the span equal to the beam spacing. The deck manufacturer's load tables provide the maximum unshored span for each profile and gage, accounting for the SDI-specified deflection limit of L/180 or 3/4 in., whichever is smaller.

Construction Load Deflection Example

For a 2VLI 20 gage deck spanning 8 ft with 3-1/4 in. normal weight concrete (39 psf wet concrete + 2.3 psf deck = 41.3 psf dead load):

w_construction = 41.3 psf + 20 psf = 61.3 psf (per foot width)
M = w L^2 / 8 = 61.3 x 8^2 / 8 = 490 lb-ft/ft = 5,880 lb-in (per foot width)

For 2VLI 20 gage: I_d = 0.262 in.^4/ft, E = 29,000 ksi
delta = 5 w L^4 / (384 E I) = 5 x (61.3/12) x (96)^4 / (384 x 29,000 x 0.262)
delta = 5 x 5.11 x 84,934,656 / (384 x 29e6 x 0.262) = 2.17e9 / 2.917e9 = 0.74 in.

L/180 = 96/180 = 0.53 in. -> Deflection exceeds L/180. Shoring required.

This example illustrates why unshored construction spans are limited — deflection at the wet concrete stage often controls over strength. Shoring at mid-span reduces the effective span by half, reducing deflection to approximately 1/16 of the unshored value.

Diaphragm Shear Capacity

Steel deck, when attached to the supporting steel with puddle welds or screws, acts as a diaphragm transferring lateral loads to the vertical bracing system. The SDI Diaphragm Design Manual provides the nominal shear strength S_n (plf) for each deck profile, gage, attachment pattern, and span condition.

Typical Diaphragm Shear Values (2VLI 20 gage, 36/4 weld pattern)

The 36/4 pattern means a weld at every flute (6 in. spacing) with a 3/4 in. dia. puddle weld plus four side-lap screws per span at the sheet sidelaps. For higher diaphragm demands, the 36/0 pattern (welds at every flute, no sidelap fasteners) provides approximately 60% of the 36/4 capacity.

Diaphragm selection note: The same deck that serves as composite formwork also provides the lateral diaphragm. The deck gage, profile, and attachment pattern must be checked for BOTH the construction condition (wet concrete) AND the final condition (lateral loads). A 20 gage deck that works for gravity may need to be upgraded to 18 gage for seismic diaphragm demands over 800 plf.

Profile Selection Decision Flow

When selecting a deck profile, answer these questions in order:

1. What is the beam spacing? Select the deck depth based on unshored span: under 7 ft to 1.5 in. deck, 7 to 11 ft to 2 in. deck, over 11 ft to 3 in. deck.
2. Is shoring acceptable? If the GC will allow shoring, a lighter gage may be used because the shoring reduces the effective span during concrete placement. Note that shoring adds cost and schedule time.
3. What is the required fire rating? 2-hour rated floors typically require a minimum of 3-1/4 in. slab thickness above the deck. The total slab depth = deck depth + concrete above deck. To minimize total structural depth, use a shallower deck (1.5 in. or 2 in.).
4. What is the diaphragm shear demand? In high-seismic regions (SDC D, E, F), diaphragm demands can reach 1,500+ plf. Check whether the default 36/4 attachment pattern provides sufficient capacity or if a heavier gage is needed.
5. Are shear studs welded through the deck? If yes, the deck thickness must support the stud welding process. 18 gage minimum for most reliable results.
6. Is roof deck or floor deck? Roof deck uses narrower-rib (NR) profiles for better insulation support. Floor deck uses wide-rib (WR) for stud placement. Do not use WR roof deck as composite floor deck — the rib geometry is not tested for composite action.

Worked Example — Office Building Floor Deck Selection

Given: 8-story office building, 10 ft beam spacing, 3-1/4 in. NWC slab, 2-hour fire rating, SDC C (moderate seismic), unshored construction preferred. Construction live load = 20 psf.

Step 1 — Span capability: 10 ft beam spacing requires 2 in. or 3 in. deck. Check 2VLI 20 gage first — max unshored span = 8.5 ft. Too short. Try 2VLI 18 gage — max unshored span = 10.0 ft. OK. Or 3VLI 20 gage — max unshored span = 11.0 ft. OK.

Step 2 — Concrete volume: 3-1/4 in. above 2VLI = total 5-1/4 in. Above 3VLI = total 6-1/4 in. The 2VLI saves 1 in. of slab depth per floor. Over 8 stories, that is 8 in. total building height savings. At 2 in. less concrete volume per square foot (17 psf), the 2VLI reduces seismic mass.

Step 3 — Diaphragm check: Assume wind shear of 450 plf at the floor diaphragm (wind-governed for SDC C). 2VLI 18 gage at 10 ft span with 36/4 pattern: phi S_n is approximately 580 plf which exceeds 450 plf. OK.

Step 4 — Fire rating: 2VLI with 3-1/4 in. NWC achieves 2-hour fire rating per UL assembly D902 with welded wire fabric 6x6 W2.9xW2.9 at the slab mid-depth. Verify with the specific UL design for the project.

Step 5 — Cost comparison: 2VLI 18 gage is approximately 3.05 psf deck weight + 39 psf NWC = 42 psf total. 3VLI 20 gage is 2.76 psf + 39 psf + additional 1 in. concrete (12 psf) = 54 psf. The 2VLI saves approximately 12 psf per floor or about 5-8% on the steel framing weight due to reduced seismic mass.

Selection: 2VLI 18 gage, 36/4 weld pattern. Unshored construction. UL D902 2-hour fire rated assembly.

Regional Standards Comparison

Frequently Asked Questions

What is the difference between Vulcraft VLI and Verco FormLok decks? VLI (Vulcraft) uses a trapezoidal rib profile with re-entrant sidewalls that provide mechanical bond with the concrete. FormLok (Verco) uses embossments pressed into the rib sidewalls that create a positive mechanical interlock. Both function as composite deck, but FormLok's embossments typically provide higher horizontal shear transfer values — which can reduce the number of shear studs required for full composite action. Always use the manufacturer's ICC-ES report values, not generic AISC formulas, when specifying FormLok.

Can I use roof deck as composite floor deck? No. Roof deck (Type NR — narrow rib) has a different flute geometry designed for insulation support and roofing attachment. The narrow ribs do not provide adequate space for shear stud placement and the profile has not been tested for composite action per AISC 360 Section I3.2c. Use Type WR (wide rib) composite deck specifically listed in the SDI Composite Deck Design Handbook.

Why does my deck need to be thicker for unshored construction? During concrete placement, the bare steel deck must support the full wet concrete weight plus construction live load without excessive deflection. A thicker gage (lower gage number) increases the section modulus and moment of inertia of the deck profile, allowing longer unshored spans. If shoring is provided, the deck can be one or two gages lighter because the shoring reduces the effective span. The cost trade-off: thicker deck is a material cost increase of approximately $0.30-0.50 per square foot per gage increment vs. shoring which adds labor and schedule cost.

How do I calculate the number of shear studs for my deck? Per AISC 360-22 Section I3.2c, the nominal strength of a shear stud welded through steel deck is Qn = 0.5 x A_sc x sqrt(f'c x E_c) <= R_g x R_p x A_sc x Fu. The reduction factors R_g and R_p account for the deck profile and stud position within the rib. For a single stud per rib in a 2 in. deck perpendicular to the beam: R_g = 0.85, R_p = 0.75. These reductions are substantial — a 3/4 in. stud that provides 26.1 kip in a solid slab may only provide 16.6 kip through a 2 in. deck. Always check the manufacturer's ICC-ES report for tested values, which may be higher than the AISC generic formula.

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Related pages

• Composite Beam Design — Steel + Concrete
• Concrete on Steel Deck — Shear Stud Design Guide
• Steel Fy & Fu Reference — Yield and Tensile Strength by Grade
• Floor Vibration Design — AISC DG11
• Beam Calculator — AISC 360 Steel Beam Design
• Section Properties Database
• AISC Steel Construction Tables
• Disclaimer (educational use only)

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