Anchorages and couplers for prestressing tendons: the value of X % and the distance a
Eurocode 2 part 2: Design of concrete bridge structures 8.10.4 (105)
The placing of couplers on more than X % of the tendons at one cross-section should be avoided (unless specific conditions are satisfied).
Where a proportion of tendons are joined with couplers at a particular cross section, remaining tendons may not be joined with couplers within distance a of the that cross section.
The recommended value for X is 50 %. The recommended value for the maximum percentage of tendons to be coupled at a section is 67 %. The recommended value for the distance a is given in Table 8.101N.