What Pressure-Locked Steel Grating Is
Pressure-locked steel grating is an open grid of load-bearing bars and cross bars in which the cross bars are forced into notches cut in the bearing bars under high pressure. The joint that results is mechanical and permanent, so the panel needs neither welding nor rivets. A pressure-locked panel stays flat, holds its dimensions and avoids the heat distortion that welding can introduce into thin bearing bars. Because the grid is open, light, air, water and debris pass straight through it while the bars carry foot traffic and equipment loads. That combination is why the product suits industrial platforms, walkways, catwalks, stair treads, trench covers, mezzanine floors and ventilation grilles.
Every grating panel is defined by three numbers: the bearing bar size, the bearing bar pitch and the cross bar pitch. Together with the span between supports they set both the appearance and the load capacity of the platform, so these values have to be agreed before the bars are pressed.
How the Pressure-Locked Joint Is Formed
In pressure locking, the bearing bars are first slotted on a press at the required pitch. Cross bars of square, twisted or round section are then forced into the slots and the displaced metal is swaged back around them. Joint strength depends on the slot depth, the fit between slot and cross bar, and the swaging pressure, all of which are controlled in the tooling rather than at the assembly stage.
| Joint type | How it is made | Typical platform use |
| Pressure-locked | Cross bars pressed into notched bearing bars, no weld | Walkways, platforms, screening panels |
| Welded | Cross bars resistance-welded to bearing bars | Heavy industrial floors, vehicle traffic areas |
| Riveted | Pressed cross bars retained by rivets | Architectural and legacy replacement panels |
| Stair tread | Serrated bearing bars plus nosing | Staircases and access ramps |
Pressure locking is generally preferred where a clean, weld-free appearance matters or where the coating has to remain continuous, because there are no weld spatter marks or heat-affected zones to touch up before galvanizing.
Bearing Bar Sizes, Pitch and Load Capacity
Bearing bars are supplied in a standard range of flat sections, and the pitch is normally 30 mm or 40 mm for platform series. The deeper the bar and the closer the pitch, the higher the load the panel carries over a given span; heavier bars are used for vehicle loads and long spans, lighter bars for short access walkways.
| Bearing bar (mm) | Typical pitch (mm) | Service |
| 20 x 3 | 30 / 40 | Light walkways, screens |
| 25 x 3 | 30 / 40 | Standard access platforms |
| 25 x 5 | 30 / 40 | General industrial platforms |
| 32 x 5 | 30 / 40 | Longer spans, foot traffic |
| 40 x 5 | 30 / 40 | Maintenance platforms |
| 60 x 5 | 30 | Heavy equipment access |
| 75 x 6 | 30 | Vehicle and trolley loads |
Load capacity is never a property of the panel alone. Span, end support condition, whether the load is uniform or concentrated, and the permitted deflection all enter the calculation. Platform specifications commonly limit deflection to L/200 or about 6 mm, whichever is smaller, and apply a safety factor to the working load. A supplier should therefore be given the design load, the span, the support detail and the deflection limit rather than only a bar size, and the load tables should be checked against that information.
Configurations for Platform Service
Flat bar grating - the standard panel for walkways, platforms and mezzanine floors, with a smooth walking surface.
Serrated grating - the top edge of each bearing bar is notched to raise slip resistance in wet, oily or outdoor conditions.
Stair treads - serrated grating fitted with a nosing and side plates, drilled for bolting to stringers.
Heavy-duty grating - thick bars at a close pitch for forklift routes and trolley traffic.
Trench and drainage covers - panelled covers in fixed or hinged frames for access to services below.
Ventilation grilles - the open area of the grid carries foot loads while allowing natural airflow.
Panels are normally detailed with banding bars or edge plates on the exposed sides, and cut-outs, hinged sections and lifting handles can be included where maintenance access is required.
Corrosion Protection and Finishing
Most platform grating is supplied hot dip galvanized to ASTM A123 or EN ISO 1461. Those standards set average coating thickness by steel thickness: 85 micrometres for steel 6 mm and thicker, 70 micrometres for 3 mm to 6 mm, and 55 micrometres for 1.5 mm to 3 mm, with lower local minima. Because the pressure-locked joint has no weld, the molten zinc reaches the internal contact faces and coats them, provided the panels are properly cleaned, fluxed and drained before dipping.
For aggressive chemical or marine service, stainless steel grades such as 304 or 316 are used instead of galvanized carbon steel. Mill finish carbon steel remains an option for dry indoor platforms where no coating is required. Stainless panels are usually supplied with a pickled or bead-blasted finish to remove heat tint and free iron.
Selection, Inspection and Installation
Selection starts from the load case, then moves to material and coating, and finally to the panel layout and fixing detail. When the panels arrive on site, the delivered lot should be checked against the drawing for bearing bar size and pitch, panel dimensions, banding and cut-outs. On galvanized panels the coating thickness is measured with a magnetic gauge and compared with the specified standard, and the joint is checked for closed, fully swaged cross bars and for any bars that have been pushed out of alignment.
Panels are fixed with welded cleats, bolted clips or saddle clamps at a minimum of four points, and the supported ends must bear on the structural steel over the full panel depth. Panels should be stored flat on timber bearers, kept clear of standing water, and lifted with slings rather than chains to avoid damaging the coating on the bar edges.
Frequently Asked Questions
Q: Is pressure-locked grating as strong as welded grating?
For equal bearing bar size and pitch the two carry similar loads. Welded grating is often selected for the heaviest vehicle loads and for very long spans, while pressure-locked panels are preferred where appearance and coating continuity matter.
Q: Which bearing bar pitch should be used for a walkway?
A 30 mm pitch gives a firmer walking surface and a larger load capacity than 40 mm for the same bar size, but it uses more steel. A 40 mm pitch is common on light access walkways and screens.
Q: Does the open area of the grid reduce the load capacity?
No. Load capacity is governed by the bearing bars, their depth and their pitch. The cross bars mainly hold the bearing bars upright and transfer local loads between them.
Q: Can galvanized grating be cut and re-coated on site?
Yes. Panels can be cut with an abrasive disc or plasma, then the cut faces are dressed and repaired with zinc-rich coating to restore corrosion protection in line with the relevant galvanizing standard.
Q: When is stainless steel grating the right choice?
Stainless steel is chosen for food, pharmaceutical, chemical and coastal installations where zinc coatings would be attacked or where contamination from zinc is unacceptable.
Q: What information is needed for a load check?
The design load and its type, the clear span, the support and end-fixity condition, the permitted deflection, the corrosive category of the site and the required coating standard.
