Hot DIP Galvanized Steel Stair Treads and Welded Bar Grating Treads with Slip Resistant Serrated Bearing Bars

A steel stair tread is a short welded grating panel fabricated with end plates and a nosing, then bolted or welded to the stair stringers. It provides a self-draining, slip-resistant step that sheds mud, water and oil instead of holding them — which is why welded treads are the standard on industrial stairs, fire escapes, access towers and plant mezzanines.

GNEE STEEL fabricates treads to ANSI/NAAMM MBG 531-17 and YB/T 4001.3, in carbon steel hot-dip galvanized after fabrication and in stainless 304 or 316. Treads and matching landings are produced in the same order so the mesh line runs across the flight.

• Tread body — a welded grating panel with the bearing bars running across the stair, spanning between the stringers.
• Carrier plates — end plates welded square to each end, 3 mm (1/8 in) minimum thickness, pre-punched for fixing.
• Nosing — welded to the front edge. MBG 531 requires a nosing on treads and at the head of stairs, both for visual safety and to carry edge loads. Nosing width is between 1¼ in and 1½ in.
• Options — serrated bearing bars for wet or oily stairs, abrasive or checker-plate nosings, side carrier angles, and toe plates.

Bearing bars must run across the flight, from stringer to stringer. A tread built the other way round has almost no capacity, and it is the mistake we are asked to correct most often on site-built stairs.

Metric flights are commonly produced at 250, 275 and 300 mm run and 700 to 1,200 mm width. One rule from MBG 531 is worth carrying onto the drawing: tread width should always exceed the tread run by at least 1/2 in (12 mm).

These are published recommended maxima for treads on a 19-W / 30 mm bearing bar pitch. Serrated treads lose section at the notch, so they are taken one size down. Treat the table as the starting point, and confirm the final bar against our tread table with your span and loading.

Nosing choice follows the duty. Rolled floor plate or checker-plate nosings are the carbon steel and stainless default; dimple nosings are also available in aluminium; abrasive nosings are specified where a higher slip class is required. MBG 531 sets the nosing between 1¼ in and 1½ in wide and requires one at the head of the stair as well as on every tread.

Four fabrication details separate a tread that lasts from one that loosens:

1. Carrier plates at 3 mm minimum, welded square, with two fixing holes per end for M12 or 1/2 in bolts.
2. A mid-span carrier plate or angle on treads 3 ft (914 mm) and longer.
3. The centre bearing bar welded at its end on treads over 9-3/4 in (248 mm) wide.
4. Welds at the third points on treads spanning 4 ft (1.2 m) or more, to MBG 533 welding practice.

Keep the nosing line continuous across the flight; a nosing that stops short on one tread leaves a trip edge. All cutting, notching and welding is completed before galvanizing, so the coating covers every fabricated edge.