When anyone thinks of landmarks in New York City, people can typically call to mind three major ones: the Statue of Liberty, the Empire State Building, and the World Trade Center. As all Americans are aware, the Twin Towers fell on September 11, 2001 due to a series of highly coordinated terrorist attacks by the Islamic terrorist group Al-Qaeda.
In this article, we break down the architecture behind the Twin Towers.
Architect and Budget
Japanese-American architect Minoru Yamasaki designed the World Trade Center and it held the title of tallest building in the world from 1972–1974. Over half a million people were accommodated by the Twin Towers on a typical weekday.
In 1962, over 40 architects were considered to design the World Trade Center, but Yamasaki and Associate Architects along with Emery Roth & Sons, were hand selected for this job. The budget was around $280 million. In today’s currency (2020), that is the equivalent of $2,400,556,024! The building’s function was to promote international trade. In an interview, Yamasaki explained, “The facility was envisioned as a physical expression of world peace and as a place for communication, information, proximity, and face-to-face convenience for a variety of business and financial stakeholders.”
"And a building must be like a human being. It must have a wholeness about it, something that is very important." - Minoru Yamasaki
Building Site
The original 17-acre site in Lower Manhattan was occupied with small retail tenants and narrow streets. Yamasaki saw this as a great opportunity to completely demolish all existing site buildings. He hoped this would “create an oasis of public space in an otherwise congested area” all while adding more subway routes beneath it. The building’s goal was 12 million square feet, and was to include an open plaza, to alleviate tension between such tall structures. Over 100 schemes and iterations were developed and proposed for this building’s superblock.
The biggest site challenge though was dewatering the site - as it easily can fill with water from the Hudson River. Slurry Walls were used along with reinforced concrete walls to prevent leakage and potential collapse.
Organization of the Towers
The Towers shared a simple plan: a 208-foot by 208-foot square, surrounded an 87-foot by 135-foot core that was composed of 47 steel columns. The core contained all of the building services—including elevators, stairs, bathrooms, and mechanical operations. A unique feature of the building circulation was the use of sky lobbies. Dividing the structure into thirds, these interchange floors were accessed by large express elevators, and provided the opportunity for occupants to switch to smaller local elevators that serviced a particular section of floors. This element allowed for the stacking of elevators, thereby decreasing the number of required elevator shafts. The floors, 4 inch thick concrete on a steel deck and supported by a 6-foot-8-inch grid of prefabricated trusses, carried the load between the core and the exterior walls, freeing the office space of interior columns.
On the exterior walls of the towers utilized vierendeel trusses. Each façade contained 59 17-inch columns on a 40-inch grid. As a result, there was only an allotted 22-inch wide window. Narrow windows was a stylistic and personal preference prevalent in Yamasaki’s work, as he feared heights.
The exterior columns were extruded 12 inches beyond the glazing, shading much of the windows, and reducing energy consumption. Towards the base of the buildings, each group of three columns merged into one, creating wider glazing for the lobby. Yamasaki originally planned to use steel as the facade material. But to save costs, a cheaper new silver aluminum alloy was developed specifically for the WTC.
On April 4, 1973, the WTC opened. It’s total price tag was $900 million dollars. That is the equivalent to $5,252,047,297.30 in today's currency.
Initial Reactions
It was heavily criticized for altering the already-beautiful skyline. However, it gradually became more appreciated. It freed up much needed public space - given the density of Manhattan. Yamasaki explained that it is the responsibility of the architect to make the most of the urban condition by considering the human scale. Yamasaki died of cancer in 1986.
September 11, 2001
On September 11, 2001, at 8:45 a.m. on a clear Tuesday morning, an American Airlines plane, crashed into the north tower of the World Trade Center in New York City. The impact left a gaping, burning hole near the 80th floor of the 110-story skyscraper. Then, 18 minutes after the first plane hit, a second plane —United Airlines Flight 175— turned sharply toward the World Trade Center and sliced into the south tower near the 60th floor.
In less than 15 minutes, after the terrorists struck the pentagon at 9:45am, the south tower collapsed after 56 minutes after being hit by Flight 175. The structural steel of the skyscraper was built to withstand winds in excess of 100 miles per hour. It also met the standards to house and contain a large conventional fire. However, it could not withstand the tremendous heat generated by the burning jet fuel. Only a few columns failed because of the explosion, but as they collapsed, the undamaged columns were left trying to hold up the building on their own. Also. the steel columns in the World Trade Center towers lost strength rapidly when the fire reached 400 degrees Fahrenheit.
At 10:30, the north building of the twin towers collapsed. Devastatingly, 2,977 people lost their lives and over 25,000 were injured.
On December 18th, 2001, Congress named September 11th a “Patriot Day” to commemorate the anniversary of the 9/11 attacks. Today, Michael Arad’s “Reflecting Absence” sits on ground zero, in the Towers’ absence, memorializing the victims of 9/11. It consists of two reflecting pools with waterfalls rushing down where the twin towers once stood.
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