Official disclaimer, I am NOT an architect or civil engineer..... but I've worked on tilt up and PIP concrete buildings enough times to remember what I've seen
in the past.
In my experience a concrete ceiling OVER an occupied space (at least in the last dozen years) is "lightweight" concrete using some form of filler, styrocrete or similiar, typically a 2-4 inch thick slab out here on the left coast.
I've never worked on parking structures, just commercial buildings and apartment complexes with large open areas. Stick welding pockets overhead, 30 feet in the air such a joy
Having said that. . DUDE THAT SCARES THE BEJESUS OUT OF ME!!!!!
Most definitely get a real engineer to look at it and run the numbers, think of it as inexpensive insurance, no engineer worth their salt will sign off on something if they aren't completely comfortable because it could come back years later and bite them in the buttocks should it fail "in normal and customary use".
Remember the shopping center balcony failure maybe 15 years ago? The decision was made to go off-prints and make unapproved modifications.... a bunch of people died because someone was cheap or lazy or both.
The only reason that I can think of for someone to use iron (expensive method even years ago) rather than a gluelam on a residential structure is that it was required for load bearing. ......