Workers casting the superstructure’s shear walls. After it is mixed, concrete must be placed within ninety minutes or it cannot be used.

The concrete was delivered in a continuous loop: load, discharge, return to the plant, reload, and go back to the site. “Most times we’d start at five or six in the morning, but sometimes it was as early as two, and there were nights where there were issues on the site, equipment problems, things like that. Once you start one of those pours you have to go until you’re done, so you’d either start real early or work real late, whatever was required.… We did pours anywhere from 200 yards to 800 to 1,000 yards. Ten yards to a truck, eighty loads a day. Not eighty different trucks. We run twenty-five to thirty trucks and rotate them back and forth all day,” Jackson said. Once on the site, Eastern could place concrete only after the steel and formwork in a given area had been inspected and certified. After the concrete was discharged, an army of workers poured it into forms or pulled it across the floor’s steel decking.

GLASS

Developing and installing the glass curtain wall presented a complex geometric puzzle. Every one of the 13,000 panels was numbered and tagged according to where it was to be placed, a system that also corresponded to the production, fabrication, and scheduling of the entire curtain wall. But before any of that could happen, Benson Industries, which engineered, fabricated, and installed the glass panels for One World Trade Center and Four World Trade Center, had to spend two years working out the logistics of crating, moving, and lifting the window units.

One’s façade is composed of 13,000 glass panels that are framed in aluminum and steel. Each unit is over thirteen feet (4 m) tall and weighs about 2,000 pounds (907.2 kg); some weigh as much as 6,000 pounds (2,721.6 kg). Only a handful of the panels were broken during installation because the glass is so strong that only a very specific kind of blow will fracture it.

The glass itself was manufactured by Viracon, an architectural glass supplier in Minnesota, and then shipped to Benson in Portland, Oregon, where the individual units were assembled. The panels were crated—four curtain wall units per each of 3,200 crates—a load size dictated by their size and weight and also by restrictions on what can be brought on a flatbed truck into New York City. Once crated, they were moved by rail across the country to New Jersey, trucked to the site, loaded one crate at a time into a hoist elevator, and moved into position for installation. A typical floor had 160 units, which were installed by Local 580, the ornamental ironworkers union. “You’re dealing with a 2,000-pound panel, so you’re not just sending one guy over to take it out by hand. You’re going to send five guys over there to lay the panel down onto a wheeled car, which then you wheel into position to be able to be picked by our floor crane to hoist it into the designated position,” Ryan Kernan, Benson’s Project Manager, said. They also had to consider the number of trades working on a given floor and the unpredictability of the weather.

Manufactured using a recipe that was specified by the architects and glass designers, the high-performance glass adheres to tight standards, ensuring that the panels match. Visual mock-ups of the units were made to be sure that “everybody’s happy with the way the glass looks and performs,” according to Kernan. “It’s minutia and micro and macro every day,” Robyn Ryan, Benson’s Project Coordinator, said. “If something is off by a quarter of an inch, or one of the bolts doesn’t have the finish specified in the approved drawings, we have to get that changed.”

More demands were made by the tower’s sloped walls. A tower crane was required to lift some of the initial curtain wall corner units, which had been assembled into large frames, to accommodate the intricate joinery of the converging stainless steel panels and the trapezoidal glass units adjacent to them. At higher levels, a floor crane with a boom arm was used to install the units at exactly the right angle. Ensuring the window units were plumb required expert surveying, assisted by computers, GPS, and satellites to configure the mean plumb of the building, which fluctuates according to the weather, the rate of thermal expansion, and other factors that come into play when erecting a supertall.

Steven Plate has served as the Port Authority’s deputy chief of capital planning and director of World Trade Center construction since 2006. He is responsible for the site’s operations, construction, financing, and environmental standards, including management of a $15–20 billion five-year capital program. A civil engineer, Plate has worked for the Port Authority since 1985. Before he was tapped to direct construction at the Trade Center, he managed the project as deputy director, starting in 2004. Earlier, he oversaw the construction and delivery of the Port Authority’s $2-billion AirTrain JFK, the elevated railway that has revolutionized commuting for millions of New Yorkers. His unstinting efforts have earned him numerous accolades, including being named an Honorary Fellow of the United Kingdom’s Institution of Civil Engineers and an Engineering News-Record 2011 Newsmaker. A native of the Bronx, Steve settled in Glen Ridge, New Jersey, with his family, where he served as mayor from 1999 to 2003.

Daniel R. Tishman is vice chairman at AECOM Technology Corporation and chairman and chief executive of Tishman Construction Corporation, one of the country’s largest construction companies. Founded in 1898 by Julius Tishman, the family firm built its reputation on innovative, cost-effective construction methods and has enlarged its scope to include solutions that are environmentally responsible. His father, John L. Tishman, pioneered the nascent field of construction management in the 1960s, serving as a conduit between owners and general contractors on a series of complex landmark projects that include the original World Trade Center, Madison Square Garden, John Hancock Center in Chicago, and Disney World’s Epcot Center.

In addition to constructing most of the World Trade Center, Dan Tishman co-chaired the 9/11 Memorial Museum Building Committee and serves on the board of the National September 11 Memorial & Museum. An ardent environmentalist and a major force in sustainable building, Tishman is the chair of the Natural Resources Defense Council. He also works with the Trust for Public Land to protect land, particularly in Maine and Colorado. In 2006, he was appointed by Mayor Michael Bloomberg to New York City’s Sustainability Advisory Board, which provided expertise and input for the creation of PlaNYC 2030, the blueprint for greening the metropolis. His firm managed the construction of 4 Times Square, the first green skyscraper in New York City; Seven World Trade Center, the first office tower in New York City to be certified under the Leadership in Energy and Environmental Design (LEED) rating system; and the Bank of America Tower at One Bryant Park, the first skyscraper in the world to be certified LEED Platinum.