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Bearing stress under a column base

Permissible bearing stress on the footing concrete under a column, with the area enhancement. Reference: IS 456:2000 Cl. 34.4.

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# Data
P_u := 2200 kN
a := 450 mm
b := 450 mm
f_ck := 25 MPa
A_2 := a*b = mm^2
A_1 := (a + 2*900 mm)*(b + 2*900 mm) = mm^2
# A_1 is the largest area of the supporting surface that is similar to A_2 (1:2 spread through the footing depth).

# Bearing
f_br := 0.45*f_ck*min(sqrt(A_1/A_2), 2) =
sigma := P_u/A_2 = MPa
sigma <= f_br =

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