Pair that focuses on bridge design requirements (5)
I believe the answer is:
specs
'pair that focuses' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'on bridge design requirements' is the wordplay.
'on' means one lot of letters go next to another.
'bridge design' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'requirements' becomes 'spec' (I've seen this before).
's' after 'spec' is 'SPECS'.
Can you help me to learn more?
(Other definitions for specs that I've seen before include "you can see right through them" , "Glasses (sl.)" , "Glasses (abbrev.)" , "Glasses (colloq.)" , "shades?" .)