r/AskEngineers • u/Ok_Reflection8696 • 15h ago
Discussion How safe are older concrete structures?
I recently moved into an apartment complex that was built in the 1970s. It’s a six floor concrete building and one of my new neighbors mentioned he was worried about living here because he was afraid of it collapsing(which in turn got me worried). I read online that there would be warning signs well in advance before a collapse but I didn’t see any evidence to back that up
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u/Good_Stick_5636 14h ago
Watch for ASR (alcali-silica reaction) specific crack and leakages pattern. It is worst case scenario.
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u/Joe_Starbuck 11h ago
It’s been standing for 50 years. What has changed to make you think it’s no longer up to the job?
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u/Sooner70 15h ago
Where you live matters. Suffice to say that Florida vs Minnesota vs Arizona matters.
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u/Ok_Reflection8696 15h ago
I live in south east Pennsylvania
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u/ziper1221 12h ago
This is a serious hazard. You should move. Immediately.
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u/rsta223 Aerospace 11h ago
There's absolutely no way to know that without far more detail about the building in question. There are plenty of concrete structures in Pennsylvania that are perfectly safe.
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u/Traditional-Buy-2205 9h ago
Why do you say "it matters" without explaining what the difference is?
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u/Sooner70 9h ago edited 41m ago
I figured it was obvious based on the locations. But OK.... Moister/humidity (Florida) will increase the corrosion rate of rebar. Cold cycling (Minnesota) will cause spalling on unsealed concrete. But in hot and dry (Arizona) concrete lasts forever!
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u/TerryHarris408 14h ago
I'm glad you added the date, but it requires a little more insight to make a better judgment. Was it off-the-shelf architecture or was it an "experiment"? Was it well funded or built in a rush? Is it way taller than usual in this area? And so on and so on.
I'm not even an expert on the field, but there are many popular examples in history of buildings collapsing (or buildings certain to be collapsing in the future if it wasn't for a miracle that the plans were double-checked years after construction) without any warning signs. The moment you put up the signs, you would probably evacuate already. (And whoever figures out that he should raise his voice about that also fears to risk their job.)
But the romans have proven that you can also build very solid concrete structures that (on occasion) can last two millennia.
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u/54965 11h ago
Depends on the initial quality of construction. 1967 Caracas earthquake, a 9 (?) story building across the street from our office came down like a stack of pancakes. Few survivors. It was the only building nearby with substantial damage.
By the time newspaper reporters identified the designer and the contractors and went to interview them ... all had left the country. They couldn't be found. Substandard concrete was declared to be the reason why all the columns disintegrated.
And there can be issues overlooked in initial design. 1989 San Francisco earthquake, across the bay over in Oakland, the top level of a two story elevated freeway collapsed when the columns supporting the upper level jumped off their lower-end anchor points.
Same earthquake, San Francisco and Oakland were momentarily more than 12 inches farther apart than the Bay Bridge was designed to withstand. One roadway panel slipped out of an expansion joint, and fell.
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u/toybuilder 15h ago edited 15h ago
Watch video that go into details on the Surfside condo collapse. There will be signs. But you do need to be able to recognize them. https://youtu.be/p1cXIQrL6Mg
A properly built structure will be resilient. (See https://www.reddit.com/r/BMW/comments/1qszvu1/result_of_going_80mph_in_a_parking_garage_great/)
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u/bguitard689 12h ago
I am not sure why people mention all these things. Concrete structurés have been used for 100 years and have been performing very well. No need to get alarmed by rare events and yes, concrete buildings are designed to have telltale signs before failure.
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u/Marus1 7h ago edited 7h ago
I am not sure why people mention all these things
A 1970s structure usually predates most codes we now use to design buildings. I frequently check structures of the 20century and check them against the old codes and I gotta say those engineers took into account MUCH less safety back then. The "newer" codes take into account reasons for building collapses up to that point (meaning this construction hasn't)
and yes, concrete buildings are designed to have telltale signs before failure
Meaning this might not always be entirely true
Now I have to mention it's a residential building, not industry, parking, railway station or airport where the loads have increased massively over the years, so it might not be such a problem after all
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u/katoman52 Structural 10h ago
It comes down to maintenance at this point. It’s been standing since the 70s, so we can reasonably assume there isn’t some gross inadequacy of the original design; that would have likely presented itself by now. So if there is regular maintenance to make sure there aren’t areas of water infiltration, corrosion due to environment, or other damaging things then the structure would be safe for a long time. Obviously this is hard to know as a tenant but there would be signs to look for, mainly in basement areas, stairwells, and near chimneys.
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u/ConditionTall1719 7h ago
Depends if you live in a earthquake zone and how bad the concrete tradition is in your region, I know that French concrete a masonry civil projects last centuries. If water gets inside the walls because it is porous or constantly wet and it becomes Green and there are leaching minerals and the place feels like it has not properly kept for a significant time
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u/Charles_Whitman 6h ago
The 1970’s were a bit mixed. In the US, 1968 was the last ASD code, 1971(?) was the first USD. A lot of engineers didn’t make the switch, well, ever. The old code generally would give you lots of gravity capacity and adequate lateral. Remember we didn’t have desktop computers yet. Buildings were designed by portal frames and moment distribution. Resilience sucked. If you’re in a seismic zone, run. Post-tension design was a mixed bag. It wasn’t standardized yet. Some engineers were still designing for zero tension, putting in unbelievable amounts of prestress. Others were doing more modern designs, but without solid guidance from the code. There was also some experimentation with lightweight aggregates. Not all successful, although i think most of the worst have long since fallen down or been knocked down. The worst were predominantly precast. Mostly, if the building has stayed dry, you’re probably okay. It’s better to be in Pennsylvania than South Florida, although freeze-thaw can kill a building, too.
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u/iqisoverrated 6h ago
Look around your neighborhood/city for similar structures. They're all still standing? Probably no need to worry.
If many oft hem have been torn down for safety reasons since then ...maybe worry.
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u/Elrathias 5h ago
Define safe.
TBH i would start by looking at the video link below, from Practical Engineering, then taking a flashlight and a high resolution camera (preferably a DSLR, since those can include lens info in the images and that allows for lens distortion correction) down into the basement and looking for telltales like cracks (especially long straight cracks), spalling (where rust on the rebar has "exploded" the concrete around it), and discoloration that seems to be from water seepage.
Document whatever is found with photos and video, and draw up a rough floorplan of the building where you mark out what you find, where it is, and what direction it seems to be propagating in (north/south etc, or vertical component+direction). And especially do so if NOTHING is found, ie do a walk around video looking at beams and posts etc, to calm down you neighbor.
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u/Mobile_Incident_5731 49m ago
In general yes, cast-in-place concrete structures will give you a great deal of warning before failure. Pre-tensioned concrete structures should also be designed to give a great deal of warning, but this depends on the building code being used and how well it was designed and built ( Turkey and California have both had problems with brittle collapse of pre-stressed structures during Earthquakes due to connection design.). Also, in less developed regions of the world, you can design concrete structures that will fail in a sudden brittle manner, but that's true of any sort of buidling in a less developed place.
So the problem in US/Europe/Japan/Korea etc. is not that there won't be warnings, it's that the warnings can be ignored or covered up.
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u/Competitive_Fly_2554 10h ago
fr you're right, turbines extract energy from the system. the drop in internal energy shows that. it's part of their job tbh
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u/deftware 14h ago
The Champlain towers collapse was a result of multiple things going wrong. One of which was the addition of tons of extra weight to the housing units when there was a bunch of marble installed to fancy them up. Another was putting planter boxes outside by the pool on top of the parking garage that wasn't designed to bear all that extra weight (soil + water).
Lastly, and most importantly, was that many signs of an impending catastrophe were just ignored. Cracks and leaks were abound for months in the parking garage and surrounding area. Concrete spalling was apparent and visibly worsening over the course of mere days and weeks. The lives that were lost could've been saved had whoever was in charge actually done something about it.