Hot-Dip Galvanized Trench Cover Grating – Load Classes & Selection Guide | From Load to Model, Get It Right
Hot-dip galvanized steel grating trench covers are the most common solution for industrial drains, cable trenches, and catch basins. The key to proper selection is: load class determines bar height, span determines feasibility, environment determines accessories.
This article systematically explains load class definitions, load-span tables for each model, selection principles, and application examples to help engineers and buyers select the right trench cover quickly and accurately.
1. Load Classes – Determine Design Load from Application
Based on application, we divide hot-dip galvanized trench covers into four load classes. Design load is the first step in selection.
| Load Class | Design Load (kN/m²) | Reference Load (t/m²) | Typical Application |
|---|---|---|---|
| Light | ≤ 2.0 | ≤ 0.20 | Sidewalks, plazas, indoor drains, cable trenches |
| Light-Medium | 2.0 – 3.5 | 0.20 – 0.35 | General factory walkways, residential roads |
| Medium | 3.5 – 5.0 | 0.35 – 0.50 | Parking lots, general factory roads, car washes |
| Heavy | 5.0 – 8.0 | 0.50 – 0.80 | Light vehicle lanes, docks, chemical plants |
Important: For frequent forklift or heavy truck traffic (>8 kN/m²), use taller bars (e.g., 50×5, 65×5) with closer supports, or switch to heavy-duty welded grating.
2. Load-Span Table for Common Models
The table below shows recommended maximum spans for common hot-dip galvanized trench cover models under different loads (deflection control L/200, safety factor 2.0). Ensure your actual support span ≤ the recommended value.
Model Explanation:
- G203/30/100: bar 20×3mm, pitch 30mm, cross bar pitch 100mm
- G255/30/100: bar 25×5mm, pitch 30mm, cross bar pitch 100mm
- G255/40/100: bar 25×5mm, pitch 40mm, cross bar pitch 100mm
- G325/30/100: bar 32×5mm, pitch 30mm, cross bar pitch 100mm
- G325/40/100: bar 32×5mm, pitch 40mm, cross bar pitch 100mm
- G405/30/100: bar 40×5mm, pitch 30mm, cross bar pitch 100mm
| Model | Bar Size | Bar Pitch | Suitable Load Class | Recommended Max Span (by load) |
|---|---|---|---|---|
| G203/30/100 | 20×3 | 30mm | Light (≤2 kN/m²) | 800 mm |
| G203/40/100 | 20×3 | 40mm | Light (≤2 kN/m²) | 800 mm |
| G255/40/100 | 25×5 | 40mm | Light-Medium (≤3.5 kN/m²) | 900 mm |
| G255/30/100 | 25×5 | 30mm | Light-Medium (≤3.5 kN/m²) | 1000 mm |
| G325/40/100 | 32×5 | 40mm | Medium (≤5 kN/m²) | 1100 mm |
| G325/30/100 | 32×5 | 30mm | Medium (≤5 kN/m²) | 1200 mm |
| G405/30/100 | 40×5 | 30mm | Heavy (≤8 kN/m²) | 1400 mm |
Span note: “Recommended max span” is the clear distance between support beams. For example, G325/30/100 under 5 kN/m² requires support spacing ≤1200mm. If actual span is larger, increase bar height or add supports.
3. Core Selection Principles
Principle 1: Load class determines bar height
- ≤2 kN/m² → bar height 20mm (G203)
- 2 – 3.5 kN/m² → bar height 25mm (G255)
- 3.5 – 5 kN/m² → bar height 32mm (G325)
- 5 – 8 kN/m² → bar height 40mm (G405)
- 8 kN/m² → bar height 50mm+ (G505/G655) and verify
Principle 2: Bar pitch affects capacity and drainage
| Pitch | Capacity | Drainage | Fall Prevention | Recommended Application |
|---|---|---|---|---|
| 30mm | High | ~55% | Good | Vehicle traffic, parking lots, chemical plants |
| 40mm | Medium | ~65% | Fair | Sidewalks, plazas, general factory areas |
Principle 3: Span is the limiting factor
For the same load, larger span requires taller bars. Never use a small bar with a large span – excessive deflection will cause cover collapse or unstable walking.
Principle 4: Frames and accessories as needed
- Unframed: Low load, direct placement – lowest cost
- Frame (angle/flat bar): Increases rigidity, prevents curling – recommended for vehicle traffic
- Hinges: For drains requiring regular cleaning – easy opening
- Anti‑theft bolts: Public areas, unattended locations
Principle 5: Serrated bars for wet/slippery areas
If the trench cover is on a ramp, car wash, food plant wet area, etc., choose serrated bars (suffix F) – friction coefficient ≥0.6.
4. Selection Calculation Examples
Example 1: Sidewalk Drain
Parameters: Trench width 400mm, support span 900mm, pedestrian only.
Load: ≤2 kN/m² (Light)
Selection: From table, Light class recommends G203/30/100, max span 800mm < 900mm → not sufficient. Upgrade to G255/40/100 (Light-Medium), max span 900mm – meets requirement.
Recommendation: G255/40/100 hot-dip galvanized cover, unframed.
Deflection estimate: ~L/250 – safe.
Example 2: Parking Lot Drain
Parameters: Trench width 500mm, support span 1100mm, car traffic (axle load ~2.5 t).
Load: Estimate 4 kN/m² (Medium)
Selection: Medium class recommends G325/30/100, max span 1200mm > 1100mm – acceptable.
Recommendation: G325/30/100 with frame (angle 40×4) for impact resistance. Optional rubber gaskets for noise reduction.
Deflection estimate: ~L/220 – comfortable.
Example 3: Chemical Plant Light Vehicle Lane
Parameters: Trench width 600mm, support span 1300mm, occasional light truck (5 t).
Load: Estimate 7 kN/m² (Heavy)
Selection: Heavy class recommends G405/30/100, max span 1400mm > 1300mm – acceptable.
Recommendation: G405/30/100 with frame and anti‑theft bolts. Note: Hot-dip galvanizing has reduced life in strong acids – consider 316L stainless steel if highly corrosive.
Deflection estimate: ~L/200 – acceptable.
5. Common Selection Mistakes & How to Avoid Them
| ❌ Mistake | Consequence | ✅ Correct Practice |
|---|---|---|
| Looking only at price, ignoring load-span table | Cover collapse, safety accident | Determine load and span first, then select model |
| Using 40mm pitch cover for vehicle traffic | Bar deformation, wheel stuck | Vehicle areas must use 30mm pitch |
| Large span with small bar height | Excessive deflection, bouncing feel | For every 10% increase in span, increase bar height one level |
| Using plain bars in wet/slippery areas | Slip accidents | Choose serrated bars (F model) |
| Ignoring frame | Edge curling, cover shifting | Vehicle traffic areas require frame |
| No allowance for HDG distortion | Cover warps after galvanizing | Keep bar length/height ratio ≤100 |
6. Quick Selection Table by Load Class
| Your Required Load | Recommended Model | Max Recommended Span | Example Applications |
|---|---|---|---|
| ≤2 kN/m² | G203/30/100 | 800 mm | Sidewalks, indoor cable trenches |
| 2 – 3.5 kN/m² | G255/30/100 | 1000 mm | Residential roads, general factory walkways |
| 3.5 – 5 kN/m² | G325/30/100 | 1200 mm | Parking lots, car washes, general lanes |
| 5 – 8 kN/m² | G405/30/100 | 1400 mm | Light vehicle lanes, docks, chemical plants |
Usage note: If your actual span is less than the recommended value, a more economical model may work (e.g., G255 instead of G325). If actual span is larger, upgrade to a taller bar or add supports.
7. Summary – Five‑Step Selection Method
- Identify the application → find design load (kN/m²) from load class table
- Measure trench support span → obtain actual span L (mm)
- Select from load-span table → ensure recommended span ≥ actual span
- Choose bar pitch → 30mm for vehicle areas, 40mm for pedestrian areas
- Specify frame and accessories → frame for vehicle areas, serrated for wet areas, anti‑theft for public areas
If you already know your trench width, support span, and vehicle type but are still unsure which model is best, please contact our engineers. We can provide a free load calculation sheet and CAD drawing to ensure a safe and economical selection.
