Mindestbewehrung zur Begrenzung der Rissbreite unter Berücksichtigung des tatsächlichen Bauteilverhaltens - Teil 1: Verformungsbasiertes Bemessungsmodell und Anwendung für Bodenplatten

Minimum reinforcement for crack width control considering the real member behaviour

It is standard practice to determine the minimum reinforcement for crack width control on base of centric restraint due to concrete hardening. Although this concept gives straightforward results, it can only be seen as a pragmatic solution which is generally not on the safe side. In detail, this simplification neglects the deformation compatibility and considers therefore not the real member behaviour. As a result of this, structural damage - especially in form of leakage in watertight constructions - often occurs.
A detailed presentation of the weakness of this empirically modified cracking force approach can be found in [1]. However, the mechanically consistent determination of the minimum reinforcement for crack width control can be achieved by considering the deformation compatibility of the restrained member, see [2].
This contribution presents the general application of the deformation-based design concept and its particular application in case of "ground slabs". A second part [3] presents the particular application in case of "walls on foundations" as well as a direct comparison with results from a cracking force-based minimum reinforcement design according to current design standards.
Altogether, the introduced approach reduces the empiricism of minimum reinforcement design significantly. The main reason is the verification of deformation compatibility along the member length. In contrast, however, the cracking force-based minimum reinforcement design according to EC2 [4] solely verifies the equilibrium in a cross section.