Raised section of uncovered rigid beam (6)
I believe the answer is:
girder
'beam' is the definition.
(I know that girder is a type of beam)
'raised section of uncovered rigid' is the wordplay.
'raised' shows that the letters should be reversed in order (going up in a down clue).
'section of' says the answer is hidden in the clue.
'redrig' is hidden within 'uncovered rigid'.
'redrig' written backwards gives 'GIRDER'.
(Other definitions for girder that I've seen before include "Steel beam" , "Metal beam used in construction" , "Structural metal beam" , "Structural member" , "Load-bearing beam" .)