Bar Grating Load Tables:
Terminology & Formulas
Load Table Calculations are based on the following terminology and formulas:
Uniform Load
Concentrated Load
U = Uniform Load - lbs/ft2
C = Concentrated Load - lbs/ft of grating width
D = Deflection - inches
F = Allowable Bending Stress
Light Duty: 18,000 psi
Heavy Duty: 20,000 psi
Aluminum: 12,000 psi
Stainless: 20,000 psi
Light Duty: 18,000 psi
Heavy Duty: 20,000 psi
Aluminum: 12,000 psi
Stainless: 20,000 psi
E = Modulus of Elasticity, lbs. per sq. inch (psi)
Light Duty: 29,000,000 psi
Heavy Duty: 29,000,000 psi
Aluminum: 10,000,000 psi
Stainless: 28,000,000 psi
Light Duty: 29,000,000 psi
Heavy Duty: 29,000,000 psi
Aluminum: 10,000,000 psi
Stainless: 28,000,000 psi
A = center to center distance between bearing bars, inches
K = number of bearing bars per foot of grating width = 12/A
t = Bearing Bar Thickness
d = Bearing Bar Depth
L = Simple Clear Span - feet
S = Section Modulus - in3/ft of grating width
I = Moment of Inertia - in4/bar
M = Bending Moment
a = Partial Load Contact Parallel to Span - inches
b = Partial Load Contact Dimension at 90 degrees to Span - inches; b = a + (2A)
P = Total Wheel or Partial Load Incl. Impact - lbs.
P1 = P per bearing bar; P1 = P x (A/b)
Light Duty, Aluminum & Stainless Steel Load Calculation:
Uniform
Concentrated
Determine S:
S = Ktd2/6
S = Ktd2/6
Determine M:
M = FS/12
M = FS/12
Determine U or C:
U = 8M/L2
C = 4M/L
Determine l:
l = Ktd3/12
l = Ktd3/12
Check D*:
D = 5UL(Lx12)3
384EI
D = C(Lx12)3
48EI
* To ensure pedestrian comfort, maximum deflection should be limited to 1/4”.
Heavy Duty Load Calculation:
Determine S:
S = Ktd2/6
Determine M:
M = FS/12
Substituting for M,
solve for L:
solve for L:
if a > L
then M = PL2/8ab
if a < L
then M = P(.25L-.125a)/b
Check D*:
D=P1[(2L3)-(a2L)+(a3/4)] / 96EI
* Maximum deflection should be limited to 1/400 span.
