Crack width verification and minimum reinforcement according to EC 2: Current model with specifications in Germany and Austria vs proposal for revision

Limiting crack widths to an acceptable level and determining the required minimum reinforcement are important tasks in the design of reinforced and prestressed concrete structures. Experience with different types of structures, ranging from watertight concrete structures to prestressed concrete bridges, shows that the concept currently applied in Germany and Austria is very effective and that significant changes are not necessary. The current draft for the revision of the EC2 (prEC2), however, presents a new concept for crack width verification and minimum reinforcement. In contrast to the concept currently used in Germany and Austria, this new concept is based more on the analysis and good reproduction of observations made in laboratory experiments and takes less account of the mechanical relationships of reinforced or prestressed concrete after cracking. For this purpose, numerous empirical factors are introduced which not only complicate the understanding but also the application in practice. However, an improvement in the accuracy of the crack width prediction is not achieved and the minimum reinforcement is significantly underestimated, especially for prestressed cross sections and thick members. In this article, the new concept set out in prEC2 is explained in detail. Its main weaknesses and contradictions are discussed by a comparison with the concept currently applied in Germany and Austria as well as detailed analysis of 2D FEM simulations with discrete cracks and adequate regard of the bond stress-slip relationship at the reinforcement-concrete interface. This should provide the basis for a factual discussion before the introduction of prEC2 into practice.