As we collectively mourn so many beautiful buildings we had lost in New York, hardly any other causes as much emotion as the Twin Towers. They perished tragically in the attacks of Sept 11, collapsing after being pierced by airplanes that turned into horrific fireballs as they hit the buildings. Twin Towers came to represent a complex mixture of pain, loss, disbelief, grief, as well as defiance, and national pride. They were chosen by terrorists because of their symbolic value to the nation, and, fallen, they acquired an even deeper meaning.

But even before the tragedy, when they just appeared on the skyline, they caused much emotion and controversy. To some, the Towers represented corporate greed, having replaced a small-shop district called Radio Row along with an ethnic Little Syria neighborhood. They were disliked by many and criticized for their “mindless Modernism.” They were viciously attacked by fellow architects. A common theme was the lack of “strength”;  Philip Johnson stated: “Just where you want strength, it isn’t there.” The New York Times architecture critic Ada Louise Huxtable wrote of the Towers, “Here we have the world’s daintiest architecture for the world’s biggest buildings.” ‘Dainty’ wouldn’t be the only epithet describing the towers. They were called ‘frilly’, ‘precious’, ‘prissy’, ‘saccharine’, ‘lacy’ and ‘epicene’. Their architect, Minoru Yamasaki, was dismissed by Gordon Bunshaft of SOM as “nothing but a decorator.”  

Philosophically, Yamasaki was more interested in designing the public space at the base of the towers rather than their tops. For him, it was more important how buildings met ground than the way they met the sky: “I had long felt that it doesn’t really matter in Manhattan how high you go up; what really matters to people using buildings is their scale at or near the ground.” He wanted to create a human-oriented public space similar to the Rockefeller Center, projecting the mood of peace and tranquility and bringing a human scale to the mammoth project. The Port Authority had hired Yamasaki for his human-oriented approach and engineering acumen. Ironically, the plaza that Yamasaki envisioned never happened due to financial restraints. Instead of an intended feel of serenity, surprise, and delight, the plaza ended up bare and minimalistic. 

Another irony is that Yamasaki, chosen out of over 40 architects to design the tallest buildings in the world, was yet to create a structure higher than 20 stories. To manage a project of that importance and magnitude, Yamasaki Associates worked with the established and experienced Emery Roth & Sons firm, dominating their New York office until the project’s completion.

The Twin Tower idea emerged out of many possible ways to satisfy the Port Authority’s requirement to distribute the ten million square feet of commercial space. Yamasaki experimented with 100 different plans and chose the twin towers concept. 

The Twin Towers, the tallest in the world, were technological marvels with several important skyscraper design innovations.

The first one was pioneering the idea of load-bearing walls in skyscraper design. At the time of construction, skyscrapers were built around grid-style steel skeletons with the support structure spread throughout the entire building. The outer curtain walls weren’t supporting a building and acted merely as skin. Yamasaki and his team figured out how to design a skyscraper with load-bearing walls by using “pinstripes” of precast concrete and steel. These narrow beams closely spaced around the perimeter carried the weight on the structure, allowing for partition-free interiors. This technique, which became the trademark of the World Trade Center towers, had two major advantages. First of all, it gave the building remarkable stability. Secondly, there was no need to place support columns throughout each floor, allowing for open uninterrupted interior space. Anecdotally, Yamasaki, who had a fear of heights, felt that the tubes placed close to each other created small windows making the building feel more secure. 

The second notable innovation had to do with forces of nature: the skyscrapers had to be able to resist high winds. Skyscrapers need to have the right combination of stability to withstand the wind and flexibility to absorb its force by moving with it. Structural models were put in wind tunnels to see how much wind they could take without collapsing. At the same time, test subjects, put into movable rooms hooked up to heavy hydraulics, were studied to determine how much sway is comfortable for humans. In the end, the towers could sway about 3 feet in either direction, and the WTC team came up with technology to minimize the sway sensation.

A considerable limitation in skyscraper construction was the absence of efficient skyscraper elevators design. The WTC crew solved it by treating the tower as three buildings stacked on top of one another, each with its own “sky lobby.” That way, instead of traveling from the bottom floor to the destination, an express elevator went from the main lobby to a sky lobby. From there, the local elevator would deliver you to your floor. Most super skyscrapers built after the WTC used the same basic system.

The World Trade Center was built entirely on a landfill. As a result, the site’s foundations had to extend down to bedrock, about 70 feet below street level. The problem was that the WTC site was located very close to the Hudson River. In order to prevent the foundation from flooding during construction, the giant bathtubs made of cement were used to keep Hudson out of the construction site. It was called the “slurry trench method,” which was previously employed mainly in subway construction. 

Not too many buildings get tested on their strength. It’s ironic that the Twin Towers, criticized for the lack of the ‘masculine’ presence and visual weakness, received the ultimate test of strength. Nobody at the time provided engineering solutions for buildings to sustain direct collision with airplanes. Nevertheless, the Twin Towers’ structural stability allowed them to stay long enough before collapsing, letting most people exit the buildings. 

During their lifetime, the Towers grew on the general public, and the city grew to love them. Their innovations are still used in skyscraper design. Their tragic demise informed future skyscraper designers of the potential design flows. Gone from the New York skyline, they became the most missed buildings in New York.

• The North Tower height – 1,368 feet.
• The South Tower height  – 1,362 feet.
• Each of the Twin Towers had 110 floors.
• Each tower’s footprint and floors were approximately an acre in size.
• There were 43,600 windows in the Twin Towers, equating to more than 600,000 square feet of glass. It took 20 days to wash them all.
• There were 198 elevators in the Twin Towers and 15 miles of elevator shafts.
• The first plane crashed into the North Tower at 8:46 am between floors 93 and 99
• The second crashed into the South Tower at 9:03 am, 17 minutes later, between floors 77 and 85
• Both 110-story towers collapsed within an hour and forty-two minutes
• South Tower collapsed at 9:59, 56 minutes after the impact 
• North Tower collapsed at 10:28, 1 hour and 42 minutes after the impact