The condition that the yield stresses in reinforcement steel will be attained can be satisfied by imposing upper limit of concrete section compression zone Xu.
Calculation rules for Xu are provided in article NEN 6720 8.1.3. These calculations rules have limited employment:
- Member is under pure bending
- Section is rectangular
- No reinforcement in compression zone
Check for limit value of compression zone for members under compression and for deep beams - not needed.
Limitation of compression zone can be also represented by limiting maximum permissible area of tension reinforcement.
Based on article EN 1992-1-1 and NEN-EN 1992-1-1 5.5 limit compression zone height can be calculated from formulas (5.10a) and (5.10b) by setting parameter of redistribution δ = 1.0. And with this limit height corresponding maximum area of reinforcement can be estimated (C.R. Braam, P. Lagendijk: Constructieleer Gewapend Beton, Cement & Beton Centrum, p.56, 2008)