Durbar load formula: Calculating ultimate load

DURBAR is a non-slip raised pattern floor plate of integral manufacture (the pattern is rolled in not welded). The “tear drop” studs are distributed to give maximum slip resistance in a variety of applications whilst ensuring a free draining surface.

The nominal gauge of DURBAR is the thickness of the plain plate exclusive of pattern.

Weight per Unit Area

Thickness on plain













Capacity Tables

It is usual to consider floor plates as supported on all four edges although stiffeners or joint covers may only support two edges. If the plates are securely bolted or welded to the supporting system, they may be considered as encastré. This increases the load carrying capacity slightly but reduces the deflection considerably.

The thickness given is exclusive of any raised pattern i.e. on plain.

The breadth is the smaller dimension and the length the greater, irrespective of the position of the main support members.

The maximum uniformly distributed load on the plate (w) is given by Pounder’s formula and the maximum skin stress is limited to the design strength py

For calculating the maximum deflection (dmax) at serviceability, the uniformly distributed imposed load (wimp) on the plate is derived as follows.

w = gdead wdead + gimp wimp

wimp = (w – gdead wdead)/ gimp

For plates simply supported on all four edges

This formula assumes that there is no resistance to uplift at plate corners.

w = a1 py t2 / k B2 [ 1 + a2(1-k) + a3(1-k)2]

dmax = a4 k wimp B4 [1+a5(1-k) + a6(1-k)2] / E t3

Where resistance to uplift at corners is provided, the above formula will be conservative. Higher values may be obtained by assuming encastré status as outlined below.

For plates encastré on all four edges

The plate must be secured to prevent uplift, which would otherwise occur at the plate corners.

w = a7 py t2 / k B2 [ 1 + a8(1-k) + a9(1-k)2]

dmax = a10 k wimp B4 [1+a11(1-k) + a12(1-k)2] / E t3


L = length of plate (mm) (L > B)

B = breadth of plate (mm)

t = thickness of the plate on plain (mm)

k = L4/(L4+ B4)

py = design strength of plate ( 275 N/mm2 or 355 N/mm2)

E = Young’s modulus (205 x 103 N/mm2)

1/m = Poisson’s ratio (m = 3.0)

gdead = load factor for dead load (1.4)

gimp = load factor for imposed load (1.6)

dmax = maximum deflection (mm) at serviceability due to imposed loads only

w = uniformly distributed load on plate (ultimate) (N/mm2)

wdead = uniformly distributed self weight of plate (N/mm2)

wimp = uniformly distributed imposed load on plate (N/mm2)

a1 to a12 are constants as below

a1 = 4/3
a2 = 14/75
a3 = 20/57
a4 = (5m2 -5)/32m2
a5 = 37/175
a6 = 79/201
a7 = 2
a8 = 11/35
a9 = 79/141
a10 = (m2 -1)/32m2
a11 = 47/210
a12 = 200/517


Information courtesy of Tata Steel.

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