On Wednesday night, residents of a 12-story high-rise in Surfside, Fla., went to bed with no reason to believe the building would collapse around them in their sleep. And then it did.
Now, we all have questions: Why do buildings suddenly fall down, and should we be worried?
It’s too soon to say what caused the building in Surfside to collapse. Some reports have said that the building had been slowly sinking into the ground since at least the 1990s, which could have weakened the foundation or led to structural problems, but the exact cause is still undetermined.
But there are several reasons why buildings do collapse, and some telltale signs to look for if you’re worried about the relative safety of your building, said Mehrad Sasani, a professor of civil and environmental engineering at Northeastern University.
Sasani has spent his career studying the mechanics of how and why buildings sometimes collapse. The Boston Globe spoke with him to see if he could provide some insight into why these tragic events can happen, and whether Boston residents should be worried.
What causes buildings to collapse?
I would categorize them to three groups. One is problems with foundation, one is problems with the structure, and one is a series of potential accidental events. Accidental events could include things such as a gas explosion, or it could be a car or a truck hitting the building.
In Surfside, it does not seem to have been an accidental cause because no one reported anything about hearing any explosions, or any car impact, or anything at all. So what is left is either a foundation problem or a structural problem.
There have been some reports about potential foundation problems in the past. So, that is certainly one important potential cause to look into. But one reservation I have is if it was really the foundation that led to collapse, there should have been warnings. There should have been cracks opening in the building.
If the structure was the cause, then there are four things to consider. One is the design process, one is the construction and inspection process, one is the potential deterioration of the structure over the past 40 years, and, finally, the state of the building when it collapsed. So any of those four, or any combination of those, or any combination of those and foundation could lead to collapse.
Can you give an example where a combination of causes led to a building collapsing?
I can give you an example of a building collapse in Singapore in 1986. There were flaws in design, flaws in construction, and overloading. I’ll explain each quickly. The flaw in the design was that the designer had forgotten to include the weight of the building. And nobody caught it.
They found out the construction was poorly done. And finally, you see, the weight of the building is a very significant portion of the load, usually the most significant portion. But because there are lots of other safety factors in design, the building had stood for 15 years. Then, a few months before the collapse, they put apparently a heavy AC system on the roof, which not only was heavy, but also introduced vibration, that, I would say, based on what I’ve seen, is what pushed the building beyond its capacity and led to collapse.
Should residents of high-rise buildings in Boston be worried?
If there is a risk of foundation failure that could lead to collapse, it should provide ample amount of warning — cracks, failures, those kinds of things. If people want to be actively involved, they can be aware of any signs of failure.
Buildings are designed in such a way that if there is a problem, we provide as much time and as many signs of failure, such that people can react, take action, and avoid such catastrophic failure.
What can residents do to stay safe?
If there are any signs, don’t take it lightly. Try to address it.
But if you live or work in a tall building, also keep in mind: Taller buildings, usually, particularly nowadays, are potentially safer, because it’s more important that the design process is done perhaps a little bit more carefully, that the evaluation is done more carefully, construction and inspection is done more carefully, because it’s more investment and larger structures.
So in general, I would not say that this class of building should in any way make people uncomfortable. Again, usually if people pay attention to signs of failure, this does not happen.