Rich,
Will the heating pipes work as a 'ground'? Sure, probably,
but you might think about it for just a while. Since the
heating system runs to all parts of the building, that means
'part' of your antenna system is running to all parts of the
building too (all those electronic devices susceptible to RF
interference, you know? Unhappy neighbors?). Any chance of
having access to the roof? That would open up quite a number
of possibly 'better' options.
And just because it's not a bad idea, have you, or can you
find an amateur group in Ankara? I'm sure they could offer a
lot of helpful advice, not just about antennas!
'Doc