# 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 f ≤ 50 MPa _{ck} | (3.19) |

λ = 0,8 - (f - 50)/400 for 50 < _{ck}f ≤ 90 MPa _{ck} | (3.20) |

and | |

η = 1,0 for f ≤ 50 MPa _{ck} | (3.21) |

η = 1,0 - (f - 50)/200 for 50 < _{ck}f ≤ 90 MPa _{ck} | (3.22) |

Note: If the width of the compression zone decreases in the direction of the extreme compression fibre, the value η f should be reduced by 10%. _{cd} |

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
`f`_{ck}- is the characteristic compressive strength of concrete, see Table 3.1
`f`_{cd}- is the design compressive strength of concrete, see § 3.1.6 (1)P.

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