BA 56/96
THE ASSESSMENT OF STEEL HIGHWAY BRIDGES

Solution:
'c' is the distance between the centre-line of the force 2Pt to the centre-line of the bolt/rivet (line 1-1).
Also note the diagram showing dimensions 'a' and 'b' is not to scale with the other diagrams; dimension 'b' is the distance between lines 1-1 and 2-2.