Steel Grating Load Capacity: Bar Grating, Expanded Metal & Perforated Options Compared
A forklift operator drives onto a platform rated for pedestrian traffic. A maintenance worker steps onto a trench cover sized for light foot traffic while carrying a 200-pound pump. These scenarios end in injury, litigation, and regulatory citation because someone specified grating without understanding what the load tables actually mean. Steel grating is not a generic product. The load-bearing capacity of a bar grating with 1-1/4″ × 3/16″ bearing bars bears no relation to expanded metal of the same overall thickness, and neither resembles woven wire mesh in failure mode. This guide examines the structural reality behind manufacturer claims and explains how to match grating type to actual service demands.
How Load Capacity Is Actually Determined
Before comparing products, understand the engineering basis. Grating manufacturers publish load tables, but the assumptions behind those tables vary. An “800 lb/sq ft” rating from one supplier may mean something different from another.
| Load Term | Definition | How It Is Tested | Where It Appears |
|---|---|---|---|
| Concentrated load | Point load at mid-span, simulating a worker’s foot or equipment wheel | Hydraulic ram at panel center; deflection measured | OSHA walkway standards; most manufacturer tables |
| Uniform load | Distributed load across entire panel, simulating stored material or crowd | Sand bags or water bags; total weight divided by area | Storage platform design; mezzanine codes |
| Line load | Load along a single bearing bar, simulating a pipe or cable tray | Weighted beam across one bar | Industrial platform design; pipe support applications |
| Impact load | Dynamic load from dropped object or vehicle crossing | Drop test or rolling wheel test | Heavy industrial; dock levelers; crane access |
| Fatigue load | Repeated cyclic loading, simulating traffic | Hydraulic actuator, thousands to millions of cycles | Bridges; high-traffic walkways; vibrating equipment |
Critical distinction: Most published “load capacity” figures are concentrated loads at a specified span with deflection limited to L/200 or L/240. They do not account for impact, fatigue, or dynamic amplification. A forklift crossing a grating creates 2–3× the static wheel load in dynamic effect.
Bar Grating: The Structural Benchmark
Bar grating is the reference standard against which other types are compared. It consists of bearing bars (carrying load) cross-connected by twisted cross bars or welded segments.
Bearing Bar Size and Load Relationship
| Bearing Bar Size (Depth × Thickness) | Weight per m² | Concentrated Load at 1 m Span | Concentrated Load at 1.5 m Span | Concentrated Load at 2 m Span | Typical Application |
|---|---|---|---|---|---|
| 19 × 3 mm (3/4″ × 1/8″) | 22 kg | 3.5 kN (790 lb) | 1.6 kN (360 lb) | 0.9 kN (200 lb) | Light walkways; platforms; catwalks |
| 25 × 3 mm (1″ × 1/8″) | 28 kg | 6.2 kN (1,390 lb) | 2.8 kN (630 lb) | 1.6 kN (360 lb) | Standard industrial walkways |
| 25 × 5 mm (1″ × 3/16″) | 42 kg | 10.4 kN (2,340 lb) | 4.6 kN (1,030 lb) | 2.6 kN (580 lb) | Heavy walkways; equipment access |
| 32 × 5 mm (1-1/4″ × 3/16″) | 52 kg | 16.8 kN (3,780 lb) | 7.5 kN (1,690 lb) | 4.2 kN (940 lb) | Forklift traffic; heavy platforms |
| 38 × 5 mm (1-1/2″ × 3/16″) | 62 kg | 24.5 kN (5,510 lb) | 10.9 kN (2,450 lb) | 6.1 kN (1,370 lb) | Truck loading; crane access |
| 44 × 5 mm (1-3/4″ × 3/16″) | 72 kg | 34.0 kN (7,640 lb) | 15.1 kN (3,390 lb) | 8.5 kN (1,910 lb) | Heavy industrial; mining; ports |
| 50 × 5 mm (2″ × 3/16″) | 82 kg | 45.0 kN (10,120 lb) | 20.0 kN (4,500 lb) | 11.3 kN (2,540 lb) | Extreme loading; custom engineering |
Values approximate for 19W4 bar spacing (19/16″ bearing bar pitch, 4″ cross bar spacing), steel S235JR, deflection limit L/200. Consult manufacturer tables for exact values.
Bar Spacing Effect
| Bar Spacing | Open Area | Relative Load Capacity | Best For |
|---|---|---|---|
| 19W4 (19/16″ bearing, 4″ cross) | 70% | 1.0× (baseline) | Standard industrial; optimal open area |
| 15W4 (15/16″ bearing, 4″ cross) | 60% | 1.3× | Heavier loads; smaller wheels; reduced open area |
| 11W4 (11/16″ bearing, 4″ cross) | 50% | 1.6× | High loads; fine heels; minimal open area |
| 19W2 (19/16″ bearing, 2″ cross) | 65% | 1.05× | Increased lateral stability; marginal load increase |
Expanded Metal Grating: Strength from Geometry
Expanded metal is manufactured by slitting and stretching a solid sheet, creating a three-dimensional diamond mesh. Its load capacity derives from the cold-worked strands and the structural depth created by the expansion process.
Expanded Metal Load Capacity by Gauge and Pattern
| Original Sheet Thickness | Strand Width | SWD (Short Way Diamond) | LWD (Long Way Diamond) | Concentrated Load at 600 mm Span | Concentrated Load at 900 mm Span | Typical Application |
|---|---|---|---|---|---|---|
| 2.0 mm | 2.5 mm | 12 mm | 30 mm | 1.8 kN (400 lb) | 0.8 kN (180 lb) | Light walkways; screens; guards |
| 3.0 mm | 3.5 mm | 18 mm | 45 mm | 4.0 kN (900 lb) | 1.8 kN (400 lb) | Standard walkways; platforms |
| 4.5 mm | 5.0 mm | 25 mm | 60 mm | 8.5 kN (1,910 lb) | 3.8 kN (850 lb) | Heavy walkways; industrial flooring |
| 6.0 mm | 6.5 mm | 32 mm | 75 mm | 14.0 kN (3,150 lb) | 6.2 kN (1,390 lb) | Heavy industrial; vehicle traffic |
| 8.0 mm | 8.0 mm | 40 mm | 100 mm | 24.0 kN (5,400 lb) | 10.7 kN (2,400 lb) | Extreme loading; custom applications |
Values approximate for standard (raised) profile, carbon steel, deflection limit L/200. Flattened profile has reduced stiffness.
Expanded Metal vs. Bar Grating: Structural Comparison
| Characteristic | Expanded Metal | Bar Grating |
|---|---|---|
| Weight for equivalent load capacity | 10–20% lighter | Heavier; more material |
| Open area | 50–80% | 60–80% |
| Deflection under load | Greater; more flexible | Less; stiffer per unit weight |
| Failure mode | Gradual; strands yield progressively | Sudden; bearing bar fracture if overloaded |
| Directional strength | Anisotropic; stronger along LWD | Orthotropic; stronger along bearing bar direction |
| Wheel load suitability | Poor; concentrated loads distort mesh | Excellent; bearing bars distribute wheel loads |
| Self-cleaning | Excellent; debris falls through | Good; open bars |
| Cost (equivalent load) | Lower | Higher |
Engineering reality: Expanded metal is not a direct substitute for bar grating in heavy wheel traffic. The diamond mesh distorts under concentrated loads, creating permanent set. Specify expanded metal for distributed loads and pedestrian traffic; specify bar grating for forklift and vehicle applications.
Perforated Metal: When Load Is Secondary
Perforated metal—sheet metal with punched holes—sacrifices structural efficiency for precision and aesthetics. It is not structural grating in the traditional sense but serves where appearance, airflow, or screening dominates.
| Hole Diameter | Pitch (Center-to-Center) | Sheet Thickness | Open Area | Concentrated Load at 600 mm Span | Application |
|---|---|---|---|---|---|
| 3 mm | 5 mm | 2.0 mm | 33% | 2.5 kN (560 lb) | Acoustic panels; filters |
| 6 mm | 10 mm | 3.0 mm | 33% | 5.5 kN (1,240 lb) | Screens; guards; ventilation |
| 10 mm | 15 mm | 3.0 mm | 44% | 4.2 kN (940 lb) | Architectural; moderate airflow |
| 20 mm | 30 mm | 5.0 mm | 44% | 11.0 kN (2,470 lb) | Heavy screens; platform flooring |
| 25 mm | 35 mm | 6.0 mm | 51% | 14.5 kN (3,260 lb) | Industrial flooring; drainage |
Values approximate for staggered hole pattern, carbon steel, simply supported edges. Perforated metal is typically backed by structural support at close centers.
Design note: Perforated metal requires support framing at 300–600 mm centers for walkway applications. It does not span distances like bar grating or heavy expanded metal.
Pressed Lock Grating: Precision and Security
Pressed lock grating uses cold-pressed interlocking between bearing bars and cross bars, creating a rigid panel without welding. Popular in architectural and security applications.
| Bearing Bar Size (Depth × Thickness) | Pitch | Concentrated Load at 1 m Span | Concentrated Load at 1.5 m Span | Application |
|---|---|---|---|---|
| 20 × 2 mm | 33 × 33 mm | 2.5 kN (560 lb) | 1.1 kN (250 lb) | Light walkways; screens |
| 30 × 2 mm | 33 × 33 mm | 5.5 kN (1,240 lb) | 2.4 kN (540 lb) | Standard walkways; platforms |
| 30 × 3 mm | 33 × 33 mm | 8.2 kN (1,840 lb) | 3.6 kN (810 lb) | Heavy walkways; industrial |
| 40 × 3 mm | 33 × 33 mm | 14.5 kN (3,260 lb) | 6.4 kN (1,440 lb) | Vehicle traffic; heavy platforms |
| 50 × 3 mm | 33 × 33 mm | 22.0 kN (4,950 lb) | 9.8 kN (2,200 lb) | Extreme loading; custom |
Pressed lock vs. welded bar grating: Pressed lock is lighter and more economical for equivalent bar sizes but has lower fatigue resistance. The mechanical interlock can loosen under cyclic loading. Specify welded bar grating for high-traffic industrial; pressed lock for architectural and moderate industrial.
Woven Wire Mesh: Not a Walkway Material
The original article grouped woven wire mesh with structural grating. This is misleading. Woven mesh is a screening and filtration medium, not a load-bearing platform.
| Mesh Type | Wire Diameter | Opening | Load Capacity | Actual Application |
|---|---|---|---|---|
| Standard weave | 1.6 mm | 6 mm | Negligible for foot traffic | Filters; screens; guards |
| Heavy crimped | 4.0 mm | 25 mm | Light foot traffic only if framed at 150 mm | Vibrating screens; architectural infill |
| Architectural woven | 3.0 mm | 10 mm | Non-structural; decorative | Balustrade infill; feature walls |
Warning: Do not specify woven wire mesh for unprotected walkway surfaces. It lacks the rigidity and predictable failure mode of grating. If used in walkways, it must be backed by solid plate or bar grating.
Trench Grating and Drainage Covers
Trench grating spans drainage channels. Its load rating must match the traffic crossing it.
| Load Class | Test Load | Application | Typical Construction |
|---|---|---|---|
| A15 | 15 kN (3,370 lb) | Pedestrian areas; green spaces | Light bar grating; FRP; cast iron |
| B125 | 125 kN (28,100 lb) | Footways; parking lots; driveways | Ductile iron; heavy bar grating |
| C250 | 250 kN (56,200 lb) | Kerbside channels; slow traffic | Ductile iron; welded steel |
| D400 | 400 kN (89,900 lb) | Carriageways; main roads | Ductile iron; heavy welded steel |
| E600 | 600 kN (134,900 lb) | Industrial areas; docks | Heavy welded steel; custom |
| F900 | 900 kN (202,300 lb) | Aircraft pavements; extreme loading | Custom engineered; heavy steel |
Per EN 124 standard. Verify local adoption; some jurisdictions use different classification.
Load Capacity by Application: A Practical Selector
| Application | Typical Load Requirement | Recommended Grating Type | Minimum Specification |
|---|---|---|---|
| Roof walkway, maintenance only | 1.5 kN concentrated | Light bar grating or expanded metal | 19 × 3 mm bar; or 3 mm expanded |
| Industrial platform, pedestrian | 2.0 kN concentrated | Standard bar grating | 25 × 3 mm bar; 19W4 spacing |
| Mezzanine, office storage | 3.6 kN/m² uniform | Heavy bar grating | 32 × 3 mm bar; 15W4 spacing |
| Forklift traffic, light | 20 kN wheel load | Heavy bar grating | 32 × 5 mm bar; 15W4 or 11W4 |
| Forklift traffic, heavy | 50 kN wheel load | Extra-heavy bar grating | 44 × 5 mm bar; 11W4 spacing |
| Truck loading dock | 80 kN wheel load | Engineered bar grating | 50 × 5 mm bar; custom design |
| Crane maintenance platform | 10 kN/m² uniform | Heavy bar grating with checkered plate | 38 × 5 mm bar; engineering review |
| Drainage trench, pedestrian | 15 kN test | Light trench grating | A15 class; 19 × 3 mm bar |
| Drainage trench, vehicle | 125 kN test | Heavy trench grating | B125 class; ductile iron or steel |
Factors That Reduce Actual Load Capacity
Published load tables assume ideal conditions. Reality degrades capacity.
| Factor | Capacity Reduction | Mitigation |
|---|---|---|
| Corrosion | 10–50% section loss over time | Specify galvanized or stainless; inspect and replace |
| Impact and fatigue | 30–60% under cyclic loading | Specify heavier grating; design for 3× static load |
| Improper support | 50%+ if span exceeds design | Verify support spacing against manufacturer tables |
| Temperature above 400°C | Yield strength reduction 20–40% | Specify higher grade; reduce allowable stress |
| Dynamic amplification | 2–3× static load effect | Design for impact; specify heavier grating |
| Eccentric loading | 20–40% reduction vs. centered | Design for worst-case load position |
Code Requirements and Safety Factors
| Code/Standard | Jurisdiction | Key Requirement |
|---|---|---|
| OSHA 1910.22 | USA | 200 lb concentrated load minimum for walkways; guardrails at 4+ feet |
| ANSI/NAAMM MBG 531 | USA | Load tables for steel bar grating; deflection limits |
| ISO 14122-2 | International | 150 mm maximum opening to prevent foot passage; load requirements |
| EN 1090 | Europe | CE marking for structural steel; execution class per consequence |
| AS 1657 | Australia | Specific load tests; slip resistance requirements |
Safety factor practice: Engineers typically apply 1.5–2.0 safety factor to published grating capacities for permanent installations. For temporary or controlled access, 1.3 may be acceptable. Never use published ultimate capacity as allowable design load.
Specification Checklist
Conclusion
Steel grating load capacity is not a single number. It is a function of grating type, material grade, geometric dimensions, support conditions, environmental exposure, and the nature of the load itself—static or dynamic, concentrated or distributed, occasional or cyclic. The tables in this guide provide starting points, but they are not substitutes for project-specific engineering analysis.
The most expensive grating is the one that fails. Underspecification risks injury and liability. Overspecification wastes capital and adds unnecessary weight. The correct specification demands honest assessment of actual loads, generous safety margins for uncertainty, and recognition that the grating must perform not just on day one but through years of corrosion, impact, and fatigue.
Referenced Standards
| Standard | Scope |
|---|---|
| ANSI/NAAMM MBG 531 | Metal Bar Grating Manual |
| ASTM A1011 | Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High-Strength Low-Alloy |
| EN 10025 | Hot-rolled products of structural steels |
| EN 124 | Gratings for vehicular and pedestrian areas |
| ISO 14122-2 | Safety of machinery — Permanent means of access — Working platforms and walkways |
| OSHA 29 CFR 1910.22 | Walking-working surfaces |
For project-specific grating selection and load verification, provide your maximum anticipated loads (static and dynamic), support spacing, environmental conditions, and applicable building code. Manufacturer load tables should be reviewed by a qualified engineer for non-standard applications or where failure would result in injury.
