On Tuesday, April 18, there were, by one estimate, about 40 cars parked in a four-story parking garage in the financial district of Manhattan. When the structure was built in 1925, it may have been one of the first purpose-built multi-story parking garages in the world, as the value of a parking place in the middle of the Roaring Twenties was probably higher near Wall Street than anywhere else and would have paid back the owners in a short amount of time. Over the years, city inspectors cited the garage for various violations, including spalling concrete and other signs of structural deterioration. None of these was apparently serious enough to cause the city to condemn the building or close it until repairs were completed.
Around 4 PM last Tuesday, the building suddenly collapsed. One report says the roof level caved in and set off a chain reaction that caused the entire structure to pancake. Seven employees were injured and the building's longtime manager, Willis Moore, was killed.
A week earlier, the city had held a news conference about its use of a new robot called the Digidog in both crime-fighting and other emergency situations. One of the fire department's Digidogs, a four-legged device painted with Dalmatian black spots on white, was sent into the collapsed building to search for survivors, and video-equipped drones probed the wreckage as well. In the event, all the survivors were rescued, some from precarious perches amid the rubble, and no firefighters were injured in trying to save them. This was the first time that the firemen's Digidog was used in a building collapse, but it won't be the last.
Buildings have been falling down ever since there were buildings. Before the modern era, the only way to learn engineering was by experience. Trial and error is a hard teacher, especially when the errors are several stories high and collapse while people are using them. But the knowledge of just what was needed to keep a wall or a tower from caving in was jealously guarded by those who needed to know, and led eventually to such amazing creations as the medieval cathedrals of Europe.
Once the properties of materials became quantifiably known and their application through mathematical principles to structural engineering became routine in architecture, it was now possible to prove mathematically that a certain structure wouldn't fall down. But that depended on the exact following of engineering plans, which were carried out by contractors and construction workers, and sometimes they made mistakes, as the engineers did too from time to time.
We won't know exactly what went wrong with the parking garage in Manhattan until forensic engineers comb through the wreckage and try to piece together the sequence of events. The fact that the building was cited for dozens of code violations, including some that involved cracks, exposed steel beams, and other signs of structural deterioration, suggests that a deteriorated member—either poured concrete or steel or a combination—finally gave way under loads that it was probably not designed to have. Photos of what may have been the roof level after the collapse show cars densely lined up on it, and cars in 2023 weigh three to four thousand pounds, a lot more than the 2200 pounds of a Ford Model A, typical of what was parked there in 1925.
The hope expressed in the early days of modern engineering was that, now that we have put the enterprise on a sound scientific footing, there is no excuse for anything to fail ever again. In reality, failure is just as much a part of engineering as success. The game is to control failure so that it either doesn't happen during the lifetime of the engineered artifact, or if it does, the failure's consequences are minor enough to effect repairs without serious harm to anyone or anything.
With buildings, failures can range from minor issues such as window blinds that don't work, all the way up to the whole structure collapsing. Obviously, more energy should be expended on preventing major structural failures, and in a regulation-intensive environment like Manhattan, few major signs of structural problems can escape notice. But what to do about them once they're noticed is another question. To condemn a building based on structural problems is a major step, and unless there is solid evidence that is rarely available, even New York City regulators hesitate to go that far.
While drones and robotic dogs are all very well, they are only useful once the tragedy has happened. Technology is now being developed at my own school (Texas State University) and around the country to make buildings more self-diagnosing: concrete that can tell you how healthy it is and whether it's developing internal flaws that would otherwise require impossibly costly means such as X-rays to determine. The hope here is that long before a building gets to the point where it might fall down, the internal diagnostic tools will alert inspectors to exactly what is wrong and how dangerous it is. At that point, the decision to repair, evacuate, or condemn can be made not on guesswork, but on quantifiable data that is presently not available.
Unfortunately, these types of innovations can practically be applied only to new construction. Nearly everything that is built already can't benefit from them, and it is in the nature of buildings to be used until something better replaces them, or until they fall down. So we will have to wait for decades until we have a built infrastructure that tells us enough about itself to allow us to make a good judgment as to whether collapse is imminent, or whether repairs can be put off for another day.
Until that happy time, we will still be hearing about building collapses from time to time. Drones and robotic dogs may become as routine as fire ladders, but in the long run, let's hope we can avert every building collapse before it happens.
Sources: I referred to articles carried by CBS News at https://www.cbsnews.com/newyork/news/lower-manhattan-parking-garage-collapse/, https://www.cbsnews.com/newyork/news/mayor-adams-robotic-dog-drone-used-to-assess-lower-manhattan-parking-garage-collapse/, and https://www.cbsnews.com/newyork/news/nypd-eric-adams-robot-dogs/, as well as the Wikipedia article "2023 New York City parking garage collapse."
No comments:
Post a Comment