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Rectangular stress distribution for the design of concrete cross-sections: the factors λ, η

Eurocode 2 part 1-1: Design of concrete structures  3.1.7 (3)

For the design of concrete cross-sections, a rectangular stress-strain distribution may be assumed as in Figure 3.5:

λ = 0,8          for fck ≤ 50 MPa (3.19)
λ = 0,8 - (fck - 50)/400   for 50 < fck ≤ 90 MPa (3.20)
and
η = 1,0          for fck ≤ 50 MPa (3.21)
η = 1,0 - (fck - 50)/200   for 50 < fck ≤ 90 MPa (3.22)
Note: If the width of the compression zone decreases in the direction of the extreme compression fibre, the value η fcd should be reduced by 10%.

where:

x
is the neutral axis depth
λ
is the factor defining the effective height of the compression zone and the factor
η
is the factor defining the effective strength
fck
is the characteristic compressive strength of concrete, see Table 3.1
fcd
is the design compressive strength of concrete, see § 3.1.6 (1)P.

This application calculates the factors λ, η from your inputs.

Input
Output
fck
MPa Table 3.1
λ
η