Deformation of non-fully cracked members which are subjected mainly to flexure, α
Eurocode 2 part 1-1: Design of concrete structures 7.4.3 (3)
The deformation may be estimated as follows:
|α = ζ αII + (1 - ζ) αI||(7.18)|
- is the deformation parameter considered which may be, for example, a strain, a curvature, a rotation, (or a deflection as a simplification, see the calculation of shrinkage curvatures).
- αI, αII
- are the values of the parameter calculated for the uncracked and fully cracked conditions respectively
- is a distribution coefficient (allowing for tensioning stiffening at a section) given by:
ζ = 1 - β (σsr/σs)2 (7.19)
- ζ = 0 for uncreacked sections
- a coefficient taking account of the influence of the duration of the loading or of repeated loading on the average strain
= 1,0 for a single short-term loading
= 0,5 for sustained loads or many cycles of repeated loading
- the stress in the tension reinforcement calculated on the basis of a cracked section
- the stress in the tension reinforcement calculated on the basis of a cracked section under the loading conditions causing first cracking
- σsr/σs may be replaced by Mcr/M for flexure or Ncr/N for pure tension, where Mcr is the cracking moment and Ncr is the cracking force.
This application calculates the deformation α from your inputs.