Applications
Welded wire mesh in composite steel deck slabs
ANSI/SDI C mandates a minimum temperature and shrinkage steel area of 0.00075 times the concrete cross-sectional area above metal deck flutes, and not less than 6×6 W1.4/W1.4 (10 gauge). On thicker fire-rated floor assemblies or longer steel joist spans, structural designers increase reinforcement to 6×6 W2.1 (8 gauge) or 6×6 W2.9 (6 gauge) on chairs.
How composite steel floor decks function
In commercial steel-frame office buildings, parkades, and institutional structures, floors are constructed by placing cast-in-place concrete over corrugated galvanized steel deck panels.
The metal deck serves two roles:
- During construction: Acts as stay-in-place formwork supporting wet concrete and construction workers.
- In service: Mechanical embossments rolled into the metal ribs lock concrete and steel together composite-action, allowing the bottom metal flutes to resist positive tensile bending moments.
However, corrugated steel deck provides tensile resistance only in the longitudinal direction of its ribs. In the transverse direction (perpendicular to the flutes) and across the top surface, concrete is vulnerable to drying shrinkage and temperature cracking.
Welded wire reinforcement (WWR) placed across the top flutes provides the required two-way crack control and structural load distribution.
Minimum reinforcement requirements under ANSI/SDI C
The Steel Deck Institute standard for composite floor deck slabs (ANSI/SDI C) and building codes specify exact minimum reinforcement parameters:
Minimum Steel Area As = 0.00075 × Concrete Area Above Flutes
Furthermore, the standard establishes that in no case shall reinforcement be less than 6×6 W1.4/W1.4 (10 gauge) (IAPMO UES ER-0981).
The table below illustrates common concrete slab thicknesses above standard 38 mm (1.5 in) and 76 mm (3 in) metal decking, along with required welded wire mesh sizes:
| Deck Flute Height | Concrete Slab Cover Above Flutes | Total Slab Thickness | Required Steel Area Each Way (As) | Standard Specified Welded Wire Mesh | Fire Resistance Rating Guidance |
|---|---|---|---|---|---|
| 38 mm (1.5 in) deck | 65 mm (2.5 in) | 102 mm (4.0 in) | 0.023 in²/ft (49 mm²/m) | 6×6 W1.4/W1.4 (10 gauge) | 1-hour standard fire rating (lightweight or normal) |
| 38 mm (1.5 in) deck | 85 mm (3.25 in) | 120 mm (4.75 in) | 0.029 in²/ft (62 mm²/m) | 6×6 W2.1/W2.1 (8 gauge) | 2-hour standard fire rating (normal weight) |
| 76 mm (3.0 in) deck | 85 mm (3.25 in) | 160 mm (6.25 in) | 0.029 in²/ft (62 mm²/m) | 6×6 W2.1 (8 ga) or W2.9 (6 ga) | 2-hour rating; high acoustic isolation |
| 76 mm (3.0 in) deck | 115 mm (4.5 in) | 190 mm (7.5 in) | 0.041 in²/ft (87 mm²/m) | 6×6 W2.9/W2.9 (6 gauge) | 3-hour rating; institutional and hospital floors |
Reinforcement placement: draped vs chaired sheets
How welded wire mesh is positioned across composite metal deck significantly impacts crack distribution:
1. Mid-depth placement on plastic chairs (Recommended standard)
The most common specification calls for flat sheets of welded wire mesh supported on specialized plastic deck bolsters or chairs resting on top of the metal deck ribs. Mesh should sit between 20 mm (0.75 in) and 25 mm (1.0 in) below the finished top surface of the slab. This position maximizes restraint against drying shrinkage micro-cracking across the top surface.
2. Draped mesh over structural steel beams
In continuous deck spans supported by structural steel girders, negative flexural tension occurs over the top flange of the support beams. In continuous designs, engineers frequently detail welded wire mesh draped over the beams to provide negative moment resistance, or add supplemental #3 or #4 rebar top bars directly over the girder lines (Roberts-Wollmann et al., 2004).
Fibres as an alternative in composite metal deck
Synthetic macrofibres and steel fibres are sometimes evaluated as alternatives to light 10 gauge welded wire mesh in composite deck slabs (Altoubat, Rieder & Junaid, 2017). While engineered fibres can provide post-crack toughness, welded wire mesh sheets remain the default industry standard because flat sheets guarantee code-mandated steel area without requiring specialized mixer batching or UL fire-rating variances.
Material procurement
- For 6 gauge (6×6 W2.9/W2.9) sheets, request a quote for flatbed delivery across Canada.
- For 10 gauge (6×6 W1.4/W1.4) composite deck minimum sheets, register your interest to reserve volume on upcoming delivery cycles.
- ANSI/SDI C, Standard for Composite Steel Floor Deck-Slabs. Steel Deck Institute.
- IAPMO UES ER-0981, Evaluation Report for Composite Steel Deck Slabs. Link
- Wire Reinforcement Institute (2026), Manual of Standard Practice: Structural Welded Wire Reinforcement (WWR-500-R-26). Link
- Roberts-Wollmann et al. (2004), Testing of composite steel deck slabs reinforced with synthetic fibers, J. Structural Engineering. Link
- Altoubat, Rieder & Junaid (2017), Fiber-reinforced concrete for composite metal deck construction, Materials and Structures. Link
Questions
What is the minimum wire mesh size for composite metal deck?
ANSI/SDI C establishes 6×6 W1.4/W1.4 (10 gauge) as the absolute minimum reinforcement across metal deck slabs.
Where should wire mesh be placed in a composite deck slab?
20 to 25 mm (0.75 to 1.0 in) below the finished concrete surface, supported on plastic deck chairs resting on the upper flutes of the steel deck.
Why does metal deck require reinforcement if the steel deck is already there?
The corrugated steel deck only provides longitudinal tensile strength in the direction of the ribs. Welded wire mesh is required to resist temperature and shrinkage stresses in the transverse direction and across the top surface.
Can I walk on wire mesh laid on composite deck?
Yes, if the mesh is properly supported on plastic deck bolsters and crew members step near wire intersections. Avoid stamping down between supports.