In EC2 clause 7.3.4(3), cover c is defined as the cover to longitudinal reinforcement. Say for a beam with cnom of 40mm and outer links of 16mm, the cover to longitudinal reinforcement will be 56mm. However, from clause 8.2.2 of PD 6687-2:2008, it states that the cover c should be taken as cnom. My understanding for cnom is that it is the nominal cover to the outermost bar, which is the outer link if it is present.
Since crack width depends very much on the concrete cover, why does PD 6687-2 propose a different definition for the cover? Should the calculation for crack width include outer link diameter? OASYS Adsec seems to include link diameter in its calculation.