usatoday24
The situation was more or less like that. For two decades, hundreds of thousands of people entered and went through the doors of one of the larger skyscrapers in New York City. These people, many of them workers, went up and down in the elevator of others totally to the critical failure that the building had, terrifying in an architectural key, and that No one took into account. Rarely in the history of urbanism of the great cities occurred A similar situation.
The story dates back to the early twentieth centurywhen the Lutheran Church of San Pedro was in a field of 53 streetbetween Lexington Avenue and the third avenue, in Midtown Manhattan. By 1960, the Church community went through serious economic problems, which led the City Council to sell the land. The negotiations were not easy and lasted years. Mainly, because the Church demanded the creation of a new separate building from the block of floors in which it could continue with its activities.
In the end Green light was given to the project. The promoter accepted the conditions, and Citi Bank commissioned Hugh Stubbins & Associates the design of the skyscraper. The engineering will be in charge of William Lemessurier. The final project consisted of a skyscraper, a church, a public space under the level of the street and landscaping.
The most important element was, of course, skyscrapers. The plane marked 46 plants that were going to distinguish from the rest of the city by the polished and anodized aluminum of the facade. In addition, among the panels there were window rows. It did not seem really complicated, at least not like the roof and the base of the building.
The happy roof
Thus, in 1977 the skyscraper ends up lifting. By then it had become bigger, with 59 plants and A total height of 279 meters. An architectural work that dazzled the city’s Skyline, a colossal tower where its inclined top of 45 degrees highlighted.
The top of the roof It resembles an isosceles triangle. The original plan was to build terraces and apartments, but over time the architects decided to install huge solar panels. Lemessurier, a professor and graduate of the Massachusetts Institute, conducted a series of tests to check their efficiency. It turned out that the energy converted by the installation was insufficient. Finally, the idea of a small solar plant was abandoned.
However, nothing like the base on which the building was supported. Some “stunches”, as Lemessurier himself described, among which he seemed to float for then seventh larger skyscraper on the planet. We refer, of course, those four gigantic pillars (34 meters each) that are located in the center of each side (instead of the corners) of the base.
It also had a single column in the center, in this narrower case, which housed the building’s elevator banks and that provided additional force to the racks. With this design it was made room for the church under the corner of the northwest of the building, and gave the giant structure A brutal effectalmost as if he were levitating. In fact, it was exceptionally “light”, of only 25,000 tons (As a reference, Empire State Building was 60,000).
The famous pillars
The base became an icon of architecture, since it caused the space in the corners to be empty. Lemessurier caused the scratch weight to be distributed to the outer skeleton. Specifically, in a grid of Marcos in a triangular way hidden under the facade. Interestingly, this structure was visible from the inside. The elements were not completely welded, but only set with screwed joints.
Apparently, the steel frame designed in this way was destined to support perpendicular winds. According to engineers, Other types of wind should not suppose a threat. In addition, municipal standards did not force other air bursts in design.
The truth is that architecture hid an important mechanism in the upper floors. Citigroup Center had One of the first tuned mass shock absorbers (TDM). It is a 360 -ton concrete sphere embedded in oil. When the vibrations of the soil or the wind moved the building, the mechanism oscillated in the opposite direction to the inclination of the building.
The problems begin
Said balancing was in turn balanced by hydraulic arms that support the sphere. With this solution, the skyscraper was able to “maintain balance.” As Lemessurier explained in his day, this piece was key, since its function was to cut the balancing of the building by half by converting the kinetic energy of friction balancing.
Once finished, the building was praised, but also The first doubts arrived. New York is not a state of great hurricanes, but it occasionally has them, what would happen if, once every 50 years, the winds will blow more than 100 km/h? These winds can blow from different directions.
The Citigroup Center was inaugurated in 1977, and only one year later it became evident that it could have A very serious defect structural.
A year later, Lemessurier receives the call that no architect expects in life. It was Diane Hartleyan engineering student from the prestigious Princeton University who had studied the construction of the skyscraper for his thesis. The first call was to ask several technical questions about the design. Hartley’s professor had expressed his doubts regarding the strength of an inclined skyscraper where the support columns were not in the corners.
Hartley made some calculations of the building’s wind load. He then compared them to Lemessurier’s calculations and discovered that the figures of construction engineers were incorrect. The student asked to be sent the exact load calculations for different types of wind. Only received data related to perpendicular winds and guarantees On the solidity of the structure.
Moreover, Lemessurier told him that the teacher had not even the most remote idea and that everything was in order. The geometry of the building frame worked perfectly with the pillars in such positions, allowing him to resist very strong winds, even from a diagonal angle.
Shortly after, the engineer receives a second touch of attention. Another student, this time from the Architecture Department of the New Jersey Institute in Newark. It was Lee Decarolis, and convinces Lemessurier to make a new calculation.
The man It begins to doubt for the first time of your project. When the new calculation ends, a cold sweat travels its head. Now the maximum load on steel triangles seemed to exceed 40% when winds blow diagonally. If so, the bolts that connect the structures were even more overloaded, together with an increase of up to 160% of the load in all connection joints.
It was known that Lemessurier was interested in the effects of an engineering change that was done during construction and that it had seemed correct at the time: the numerous joints did not soldie (as it was in the original design), and secured with bolts (screws). Normally, this change can be acceptable, but the design of the Citicorp center was sensitive to diagonal winds. Hence the results of their calculations were more than worrying.
Discovering the cake
To get an idea of what the engineer had just discovered, let’s think that the force of the wind on the flat surfaces of a building is huge. The wind that pushes against a high architecture like those of the skyscrapers has a Great influence against its basealthough gravity does much of the work for maintaining the entire building together through compression.
This makes a building safe against the wind, as long as the joints are strong enough to resist any force that is not counteracted by gravity. In the case at hand, Lemessurier feared that the screws were not too strong for the task.
After a few days without leaving home, the engineer contacts lawyers and other specialists to agree on a process with which to rectify his mistake. They confirm that bursts more than 100 kilometers per hour would be enough to break the bolts that support the bases of the building, resulting in a “very serious” structural failure.
Shortly after, the workers begin repair work at night, there is no time to lose before a possible catastrophe of unpredictable consequences. Meanwhile, life was still working “normal” inside the skyscraper. The engineer’s plan: reinforce the 200 joints Solding 5.1 cm thick steel plates to cover the bolts.
In addition, the integrity of the columns and the entire skeleton was constantly verified, they could not afford the lightest failure. The roof concrete ball It was assured Regarding access to energy sources. That said, Manhattan had a plan in case of collapse, one who never made public so that anyone panic.
The truth is that the reinforcement plan ended at the end of 1978, a year after the structural failure was known, but nobody said anything. The case was uncovered in 1995 with An article from the New Yorker Describing what happened almost twenty years ago, bringing to light, now, the historic failure with which the skyscraper rose.
However, neither Lemessurier, nor the architects and engineers of the Citigroup Center, had to face legal consequences for the correction of their mistakes. Apparently, the cost of the modifications made amounted to several million dollars, an amount that was covered by the company’s insurance.
Today and according to the new calculations, every several hundred years there are winds that can seriously damage a building. We will never know what would have happened not to have fixed the citicorp, but we do know the name of the heroine that, perhaps, saved thousands of life: Diane Hartley.
Image | Andrew Moore, Elisa.rolle, Johan Burati, TRXR4KDS, Max Hermus, Love.raavi
In Xataka | 900 years ago, Europe had its own Manhattan: the impressive skyscrapers of more than 100 meters in Bologna
*An earlier version of this article was published in July 2024
GIPHY App Key not set. Please check settings