SteelGratingCalc
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Tool 02 · NAAMM MBG 531 / BS 4592

Bar Grating Load Capacity Calculator

Calculate the maximum allowable uniform distributed load (UDL) and point load for any steel bar grating specification. Supports NAAMM MBG 531 (allowable stress method) and BS 4592 (UK limit state). Bending and deflection checks included.

Bearing Bar Specification

Span & Design Conditions

Distance between support centrelines

Calculation Method

Section Modulus (per bar):

S = T × H² / 6 (mm³)

Moment of Inertia:

I = T × H³ / 12 (mm⁴)

Bars per metre width:

n = 1000 / P_bb

NAAMM allowable stress:

σ = 0.55 × f_y (MPa)

UDL allowable (kPa):

q = 8·σ·S·n / (L²·1000)

Deflection check (NAAMM):

δ ≤ L / 180

E = 200,000 MPa. Fixed ends use coefficient 16 (bending) and 384 (deflection). Results are simplified allowable-stress estimates — always verify with a structural engineer.

Load Capacity Results

NAAMM MBG 531

Max Allowable UDL

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Max Point Load (per m width)

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Deflection at Max Load

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Governing Check

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BS 4592 Load Class

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Results are theoretical estimates using simplified beam theory. Always verify structural adequacy with a qualified engineer before installation.

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Frequently Asked Questions

Which design standards does this calculator use?
NAAMM MBG 531 (US standard, allowable stress 138 MPa / 20,000 psi for A36 steel) and BS 4592 (UK/Commonwealth, Parts 0–5). Toggle between them using the Standard selector.
What is the maximum recommended span for steel grating?
Generally 1,200–1,500 mm for standard pedestrian loads with 25mm bearing bars. Beyond 1,500 mm, deflection typically governs. Use heavier bars (30–40mm height) or reduce pitch for longer spans.
What does 'deflection controls' mean in the results?
It means the grating can carry more load before yielding than before it deflects excessively. NAAMM limits deflection to L/180 and BS 4592 to L/200. When deflection controls, the allowable load is lower than the bending capacity.
How does end condition affect load capacity?
Fixed ends provide roughly 60% more capacity than simply supported ends — a fixed-fixed beam has a plastic moment resistance 1.5× higher. Use 'Fixed Both Ends' only if the grating is welded or clamped into its frame, not just resting on supports.
How do I determine the BS 4592 Load Class?
The calculator outputs the class automatically: Class A (2.0 kPa, light pedestrian), B (5.0 kPa, normal industrial), C (7.5 kPa, forklift aisle), D (10 kPa, heavy vehicle) and E (>10 kPa, special loads).