The quantification of the necessary reinforcement for crack width control in highly restrained RC slabs still remains a subject of discussion in both scientific and practitioner communities, particularly when the simultaneous effects of applied loads and restrained shrinkage deformations are considered. Indeed, different authors/designers follow distinct approaches to deal with the problem. This is however a very important matter, because in slabs, the quantity of reinforcement is frequently determined by Service Limit States (SLS) of cracking. Therefore, the use of different design criteria for SLS can bring different performance levels, and also different global costs (e.g. reinforcement can be overdesigned, or under designed and then repairs may be in order). In such context, this paper presents and analyses the results of a design challenge launched by the research teams at UMinho and UPorto to a set of design offices. The design challenge consists in the sizing of the necessary reinforcement to satisfy adequate cracking performance in a highly restrained slab. All information about geometry, materials, loads and boundary conditions are provided in the design challenge sheet provided to participants. A total of 7 teams have provided answers to this design challenge. Results are treated anonymously in regard to participating teams. A discussion is held with basis on common and differentiating points, and finally an analysis of the authors using non-linear finite element analysis is made, targeting to better assist interpretation of the expectable behaviour of reinforcement solutionsPortuguese Foundation for Science and Technology (FCT) to the Research Projects PTDC/ECM/099250/2008, EXPL/ECM-EST/1323/2013 and PTDC/ECM-EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Units ISISE (POCI-01-0145-FEDER-007633) and CONSTRUCT (POCI-01-0145-FEDER-007457) is gratefully acknowledged. A word of acknowledgment is also given to the participants in the design challenge, with fundamental importance for the discussion held herein. The authors would also like to acknowledge the benefits of cross-linking research through the network of COST Actio
