Large framework horse hauled up with effort (6)
I believe the answer is:
gantry
'large framework' is the definition.
'horse hauled up with effort' is the wordplay.
'horse' becomes 'nag' (term for an old horse).
'hauled up' says the letters should be written backwards.
'with' is a charade indicator (letters next to each other).
'effort' becomes 'try' (synonyms).
'nag' backwards is 'gan'.
'gan'+'try'='GANTRY'
(Other definitions for gantry that I've seen before include "Overhead structure supporting equipment" , "Support for, eg, crane" , "Support for a travelling crane" , "Bridge-like framework for moblile crane" , "Support for overhead work" .)