If it is common property then it is Strata reasponsibility to maintain which would be the best soloution in this case
BUT
If the stairs were installed by current resident then they are reasponsibile.
If they were installed by a previous owner and no bylaw registered the reasponsibility falls back on the strata once ownership changes.
If a motion was passed authorizeing the origional stairs to be installed by the owner at their cost but no bylaw registered then I would suspect that that the Strata would have to accept reasponsibility.