When I look up Steamrail Victoria I get a rail preservation group.
Do you think these are the people who own the area you are interested in?
If it is then I would contact them and explain your photographic interest in the place, instead of talking to security who most likely have no say in the matter anyway.
If the building where owned by some property developer then I imagine they would have no interest in letting you in, but a preservation group could likely see it differently and might let you in escorted by a member of their group.
Here is contact info if I'm on the right track http://www.steamrail.com.au/contactus.php
Our local in Adelaide is the SteamRanger Heritage Railway.
I turned up early one morning to their rail yard where I knew they would be steaming up for a public steam run that day, and though it was a non public access area I asked the first person I came across who I should talk to to ask permission to take pictures and it was no problem at all from there.
Showing interest and asking nicely is enough usually with these sorts of groups.