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Social responsibility of engineers

In a city of skyscrapers of nearly every shape and size, the Citigroup Center on Lexington Avenue is one of New York’s most unique. Resting on four stilts perfectly centered on each side. The original structure responsible for these striking features also contained a grave oversight that nearly resulted in structural catastrophe.

In the early 1960s, Citicorp’s headquarters became too small for the company’s ongoing growth and expansion. So it spent about $40 million to acquire all of the St. Peter’s Lutheran Church was selling, but the new building could not have any structure across the church.This meant that the entire building would need to hover above the church, nine stories above street level, presumably by placing it on piers. More importantly, preserving the church meant that none of the supports could be located at the corners of the lot, resulting in a design that moved the columns to the middle of each profile. Upon its completion in 1977, the Citigroup Center became the seventh tallest building in the world.

Most of the credit for the project is generally given to its structural engineer, William Le Messurier. Working on an enormous scale with an unprecedented massing configuration, the task of inventing a structural system to support this unusual design fell squarely on his shoulders. Le Messurier devised a V-shaped system of braces that spanned the building in eight-story units, resulting in five sets of inverted chevron-like supports. In textbook diagrammatic form, these braces redirect the downward forces of the building toward its center where the load-bearing piers transfer them to the ground, all the while providing resistance to the horizontal forces generated by the wind.

Shortly after construction was finished, Diane Hartley, an undergraduate architecture student at Princeton, attempted to mathematically replicate the performance figures of the building. When she calculated the force of wind applied directly to the side of the tower, the structure had no problem offsetting it. However, she went a critical step further, calculating the effect of quartering winds—that is, winds that strike the building from two sides simultaneously—and found that above a certain windspeed, the joints of the building would buckle and catastrophic failure was imminent. She phoned Le Messurier’s office to find out where the figures had gone off. Fortunately, Le Messurier decided to look into the student’s questions.

The survey found that a late-stage cost-cutting measure that substituted fully welded joints in the spliced diagonal braces for bolted joints resulted in insufficient strength to withstand the quartering winds, and given the wrong combination of forces, the building could eventually collapse. In other words, Hartley’s figures were correct

Le Messurier quickly handed the figures to several meteorological experts to determine how frequently the wind speeds necessary for structural failure occurred in New York. The answer was sickening: every fifty-four years, they said, unless a storm cut off power to the tuned mass damper, which would reduce the frequency of potentially catastrophic storms to a mere sixteen years.

On hearing the news, LeMessurier thought about staying silent and committing suicide, but LeMessurier chose the third option, saving the building. "I had information that no one else in the world had," LeMessurier recalls. "I have the power in my hands to achieve extraordinary events that only I can initiate."

Le Messurier hurriedly contacted the executives at Citigroup to let them know that their brand new, $175 million icon could easily become the greatest disaster in New York's history. Together, they hatched a plan to superimpose fully welded steel plates over the weak joints on the braces, and began fortifying the building around the clock while keeping a watchful eye on the weather forecast.

During the repairs, the weather center received the news everyone had feared -- a major storm: Hurricane Ella, bearing down on New York. It had winds of 125 miles per hour and was a Category 4 hurricane at its peak. "No one dared say, 'We might hit the emergency button,'" LeMessurier recalled. The emergency button means more than 200,000 people may need to evacuate. "No one dares say that. But everyone is bleeding from the bottom of their hearts." Luckily, as it neared New York, it miraculously changed course and headed unexpectedly deep out to sea.

In the end, restoring was completed, and the building became one of the safest skyscrapers in New York City, able to withstand a once-in-700-year storm without the help of dampers.

Diane Hartley certainly deserves much credit for starting the incredible chain of events that may ultimately have saved thousands of lives. But her discovery would have never made a difference if it was not for LeMessurier’s willingness to consider what others questioned. LeMessurier listened to the thoughts of an unknown college engineering student and intellectual curiosity and inquisitive nature prevented him from completely disregarding the student’s inquiry. Instead LeMessurier considered the message from the student.

 LeMessurier’s acts highlight the importance associated with constantly questioning and re-examining past decisions in light of new information or ideas. Design professionals must be open to other ideas, perspectives and criticisms while avoiding a “stubborn attachment to existing beliefs.”

Just as the words of William LeMessurier to his students at Harvard: “You have a social obligation. In return for getting a license and being regarded with respect, you’re supposed to be self-sacrificing and look beyond the interests of yourself and your client to society as a whole. And the most wonderful part of my story is that when I did it, nothing bad happened. ”

（内容来源：

https://www.archdaily.com/564014/ad-classics-citigroup-center-hugh-stubbins-william-le-messurier

https://www.theaiatrust.com/whitepapers/ethics/LeMessurier-Stands-Tall_A-Case-Study-in-Professional-Ethics.pdf）