What could have caused a 12-storey building to collapse in Miami all of a sudden?

12-storey building to collapse in Miami all of a sudden.

There are a number of possible causes. I tend to lean toward erosion of part of the foundation from underground water. It is well known that the water table in FL is close to the surface. It would be very useful to study the geotechnical reports and boring logs of the construction of the new building at 8701 Collins Ave as compared to the design of the subject structure. In addition, it is very interesting to note that there are no other large structures in the area of North Beach Oceanside Park to the south on both sides of Florida State A1A down to North Beach. It’s too early to tell. I saw the pictures.

Picture source: BBC news report.

Collapses like this normally do not occur due to structural failures. The same columns and beams are still standing in the adjoining part of the building. If it was a structural deficiency the collapse would have occurred earlier when the building was fully loaded. The fact that it stood all these years makes any structural deficiency unlikely. The detailed structural design drawings and the analysis and design records (if still available with the architect and structural engineer) will no doubt be studied and experts will decide if there was a design problem. I doubt if they will point to structural design deficiencies as a cause.

This extremely unusual collapse without warning appears likely to be from a combination of factors. It doesn’t seem that a sinkhole gradually developed over years could be responsible, since there would have been severe settlement cracks and sagging structure.

It’s telling that the building stood over an underground garage. Engineers had recently inspected and found serious damages, although no emergency alarm was raised.

Possibly, the quality of concrete was poor or inconsistent during construction, and/or curing intervals were rushed between successive floors, producing critical fracturing and fragmentation throughout the main supports, and that would have been subject to a final-straw trigger, whether by further decay or even by time alone (weight is a constant acceleration force).

Also, I think investigators and regulators are going to have to look at how the building’s total structure and mass were changed over the 40 years since it was built.

That real estate was prime in 1981, but not nearly as much as it is today. That could mean the original total mass may have been lesser and/or the original load capacity might have been more robust than when it fell, due to lighter weight materials as built, and possibly more solid load-bearing walls, as compared to (hypothetical) more recent major remodel work done in the residential units, including added tons of granite countertops, tiling, and structural changes to load-bearing walls and beams.

Normally, if done properly those changes wouldn’t create a collapse risk, but when coupled with a compromised foundation, that could explain a sudden catastrophic failure without typical indicators.

Did the sinking cause this? We don’t know at this point. My guess is that there was some questionable construction combined with an unforeseen stress on the building. That’s the usual culprit.

Settling is avoided by using piers that are deep enough to reach soil that can’t compact. Usually bedrock.

The depth of the piers varies depending on local conditions, but in Florida they have to be pretty deep.[3] The state sits on a bunch of squishy rock filled with water and some large buildings have gone over 170′ down to get past it. It’s terrible for highrise buildings. It’s also very expensive. It’s possible that they managed to get away with building substandard piers.

The other part, which we can’t possibly know yet is in the construction of the building itself. A failure like this is the result of too much concrete and not enough steel. Specifically, the building used rebar reinforced concrete supports to hold the whole thing up. Those failed catastrophically.

On page 36 of the ’79 plans they show a lot of rebar that I don’t see in the collapse pictures on the left side of the point of separation. #4 (1/2″) rebar hooks at 10″, every floor . I built buildings like this, overseeing the re-bar.

It appears nothing but un-reinforced concrete floor was holding this section up. It may be that one floor fell leading to a cascade. There is no rebar hanging out of the wall like the other section. It would be hanging every floor. The plans show it, the picture does not. The roof deck level had rebar, you can see where it pulled out from the elevator and stair towers.

This can indeed potentially damage the foundation. FIU professor: Collapsed Surfside building showed signs of subsidence in ‘90s

There is a Florida International University professor who conducted studies of the area for decades and claims that the place where the building stands has been sinking a few millimeters every year since the 1990’s. The building originally stands on wetlands or sandy ground so it makes sense that it would be sinking over time. Add in the fact that the barrier island where Surfside is located along with Miami Beach and Bal Harbour has been having issues with periodic seawater flooding, you can see another problem, which is saltwater intrusion. The people who are saying sinkholes as answer to this question don’t know Florida very well; sinkholes are more of a Central Florida thing. I’ve never heard of a sinkhole incident in South Florida.

Another possible explanation could be the fact that the building is located in a coastal region, Miami. The salt in Miami's coastal air could have potentially facilitated the erosion of steel, which in turn led to a structural failure.

Here’s one in the front of this picture. it’s only the level of one floor. These tall buildings need large, multi story support columns that are strongly tied into the rest of the structure to prevent this sort of collapse. What you’re not seeing in this picture is a lot of structural steel in any form. It’s mostly concrete. What’s here is probably acceptable under the local building codes.

You can see from the section that survived that the way the whole thing was built using concrete with some reinforcement. That’s not a design that can survive a lot of movement. (As a Californian, that’s something we have to build for. We have earthquakes. You are never going to see a collapse like this in my state.)

In conclusion, I think that there are probably a few factors at work here:

1. A design and local building codes that permit the building of structures that don’t account for stresses caused by movement.
2. Piers that didn’t reach bedrock and therefore allowed for uneven settling.
3. Possible substandard building through graft that skimped on important structural elements that provided a safety margin in case of building movement.

[1] Collapsed Miami condo had been sinking into Earth as early as the 1990s, researchers say

Only a detailed inquiry by experts, who will review the structural designs, and also inspect the site after the rubble is cleared can establish the most probable cause.

Two possibilities strike me.

One is that a sink hole developed under the building.

The earth simply sinks. No engineer can design a building to stand if that happens.

It is just an act of God. That is all I can say.

If it is not a sinkhole, the probable cause is that the foundations have been sinking slowly, millimeter by millimeter, over a long period of time and today’s sinking was the straw that broke the camel’s back. Any building, however strongly built, is only as strong as the foundations. The foundations are in turn supported by Mother Earth. If Mother Earth fails then nothing can save the building.

All this is just a guess. Mine can be treated as an “educated guess” since I am a retired structural engineer.

But sitting on the other side of the globe with no access to any technical information, this is all that I can offer.

Building collapses are common in India particularly in the city of Mumbai during the rainy season where many buildings are almost a hundred years old and they were built using concrete and steel of less strength than available today. But I am surprised that it has happened in the USA.

I pray for those trapped under the debris and hope all of them will be rescued and that the fatalities will be minimal.

Picture Source BBC