We also get involved in refurbishment of staircases and fire escapes when the cost of replacement for a new one is prohibitive.
This shows the staircase  before, during and after lifting back in position (using our portable gantry). 
We replaced the outer stringers (200 x 10 flat bar). Drilled the 12mm holes for the treads, cleaned down the treads, treated them with rust neutraliser and bolted them back together on site, To complete we painted them with zinc phosphorus primer, lifted them back into position and finished with a back top coat.