I grew up partly in an 18 story reinforced concrete building built in the 1920s. The apartment I lived in was recently sold for several million dollars.
Once, when there was a leak and the plaster came off, the underlying concrete was exposed and it scraped away like very weak sandstone.
How strong is the building and when will it collapse? Does anyone know? Is anyone testing?
I think the answer to both of those questions is "no". Everyone seems to assume they will stand forever. They won't.
None of the owners want to know that their investments are worthless. So nothing will be checked unless its required by law.
Also, buildings don't fall all of sudden. You would get a lot of cracks and problems before your building collapses
In first-world countries/states with earthquakes, the answer to this is often yes and yes.
A good article from 2000 in Christchurch discusses the issues: https://www.canterbury.ac.nz/media/documents/event/Hopkins-L...
The article is relevant because Christchurch had a major earthquake in 2011. I know of quite a few older buildings that were retrofitted that did not even need to be demolished (most buildings are designed to just survive a major earthquake, but often they need to be demolished due to damage, similar to writing off cars after accidents).
Christchurch did have regulatory failures because many older buildings were known to be unsafe (e.g. only meeting 10% of current code/regulations), but owners could defer fixing them up to code almost indefinitely. But that regulatory failure is being addressed in other parts of the country e.g. Wellington.
The South Island of New Zealand is overdue for a magnitude 8.2 Earthquake which will devastate many towns on the West Coast, and will affect the whole country indirectly. https://www.stuff.co.nz/the-press/news/90364889/magnitude82-...
You can sometimes see where concrete of a building has been tested for example a circular hole about 10cm across is left where a sample was taken.
If interested, next time you meet a civil engineer or someone working in the relevant department that deals with the building codes will often know relevant details about your location.
In a few minutes searching I didn't find any reference to required testing of old buildings for structural or materials integrity.
That makes no sense. If I am buying property, it is in my best interest to make sure it isn't going to fall apart. Especially since if something happened due to my negligence, I would be responsible.
If you have no idea of whether or not the building is being inspected, why would you make the assumption it's not?
They certainly do in earthquakes. Even in areas that nominally don’t have earthquakes, some parts of the building code will surely be about ability to withstand a rare earthquake.
And ‘trust but verify’ is important - there are a lot of assumptions people make about what is actually checked or verified that are, well, just wrong. About a lot of things. And if you can’t find anyone saying it is happening, it very well might not be.
To the prior poster - call the NYC building department. Here is a link to their FAQ/index page and it should be straightforward to find from there. They are the ones responsible for making sure buildings don’t randomly collapse in NYC.
https://www1.nyc.gov/site/buildings/business/inspections.pag...
UK also has a history of major failured in construction practices and inspection, where chunks of a new apartment block suddenly collapse like in Ronan Point, or a recently renovated tower block goes up in flames and half of residents die despite them warning about issues for years.
I wish living in first world country guaranteed sensible things are happening, but it doesn't
https://www.theguardian.com/environment/damian-carrington-bl... https://en.wikipedia.org/wiki/Ronan_Point https://en.wikipedia.org/wiki/Grenfell_Tower_fire
One exception is the mandatory retrofit programs implemented by some cities like San Francisco and Los Angeles.
False.
Large structural failures can be catastrophic and unexpected.
Buildings can and do collapse quite suddenly. The examples here are not necessarily caused by reinforced concrete failures (though several cases make use of reinforced concrete --- generally other failures lead to the collapse). But the final failure of a system under load and near its structural limits can be quite sudden.
Taiwan bridge: https://youtube.com/watch?v=OSCPUGHUyIs https://youtube.com/watch?v=WqHXMswLwPM
Minnesota I35W bridge collapse: https://youtube.com/watch?v=CMdv2wRaqo4
Jerusalem dance floor: https://youtube.com/watch?v=5UOb7RBWlak
Morandi bridge, Italy: https://youtube.com/watch?v=V479srTBlAk
Hard Rock Hotel New Orleans (under construction): https://youtube.com/watch?v=WC8k5unvyfU
Sampoong Department Store, Korea (visualisation): https://youtube.com/watch?v=aQXTSR9koCg
The Kansas City Hyatt Regency skywalk collapse (1981) would be another instance. I don't believe there's video of the failure itself, though Grady from Practical Engineering has a great explainer of what went wrong: https://youtube.com/watch?v=VnvGwFegbC8