“The challenge is bringing the other stakeholders and showing them how to do high-rise construction – they’re not high-rise constructors,” Johnson says. “Logistics is a huge challenge down here.”

Building Information Modeling is being used throughout design and construction. One foresight of the Silverstein team was to set up a design room on the 10th floor of 7 World Trade Center in 2006, where up to 120 people worked together in an open-office environment, representing all the different designers, and, eventually, the construction managers as well.

Tower 3 started foundation work in June, and will begin superstructure in the beginning of 2010; steel is scheduled to top out in the winter of 2013, followed by the curtain wall and a Spring 2015 opening. Johnson expects well over 1,000 people on the construction site at its peak. Like the other projects, the equipment is heavy — two steel cranes already on site, and a climber or tower crane coming on for the concrete. Even though the tower is in the early stages, Johnson sees a difference this year.

“Last year and the year before, [the mood] wasn’t as good,” he says. “The trades are hungry. They want to get out there and work.”

Tower 4

Scott Thompson, Silverstein’s project executive on the tower, came on in February 2008, when procurement was just beginning.

“It was a good time to start,” he says. “I had great enthusiasm to get this thing built and show our resolve. Then we had some mishaps, some slowdowns, some arbitration issues.”

The Maki-designed 64-story Tower 4 at 150 Greenwich is scheduled for completion in the fall of 2013, the first tower up. Again, the emphasis is on mixed use: in addition to the 2.3 million sq ft of office space — two-thirds of which will be occupied by PANYNJ, the rest leased out by Silverstein — the tower will house retail on the first five floors, two of them below grade. Unlike its neighbors, the floor plate of the tower will be in the shape of a parallelogram on floors 7 through 46, and a trapezoid on floors 48 to 63. The core itself will reflect the shape as well: on the west side, facing the memorial, it will run 45 ft wide, and 35 ft on the east side. LEED Gold certification is the aim for Tower 4 as well.

Some of the challenges on Tower 4 are the same as the other projects: the extra reinforced concrete, 26,000 tons of steel — some pieces are 65 ft long and weigh 110 tons — the extent of engineering the core and structural steel, going 85 ft below ground, and working on a cramped site, having to share egresses for deliveries while passing them all through security. Thompson’s team, however, took on some additional work, and not just the base building mechanical systems.

“The whole 16-acre site, four to five massive projects at once—the logistics in its own right is mind boggling,” he says. “Then you get to the nitty gritty of Tower 4 itself. You have all the infrastructure within the building, and we took an extra task on, to coordinate not just our work but the additional stakeholders — the retail, the Hub, and the [Vehicular Security Center] — we took on the task of coordinating all their work. Installing inserts, sleeves — a lot of this concrete is 12,000 psi, some walls are 3-ft thick — we’re not boring later to get a pipe through, so we’re getting the sleeves in now.

“ Everyone wants the ultimate goal and different ways to do it,” he says. “We’re here to bring everyone in the fold, to make sure it happens in the correct way.”

After an initial setback during the foundation stage on Tower 4 , the building reached grade in the beginning of last year and started steel and concrete core work, going to 80 ft by August. In November, the team plans to complete one floor a week from the eighth floor up.

“We knew we were going to build this thing eventually,” Thompson says.

The Memorial

Architect Michael Arad and landscape architect Peter Walker, following a worldwide competition that yielded 5,200 entries, designed “Reflecting Absence,” the World Trade Center memorial.

Instead of a new above-ground structure, the design converts the two footprints of the original Twin Towers into cascading waterfalls leading 30 ft down below ground to illuminated pools. On its perimeters, the waterfalls will have inscriptions of the 2,979 killed in the Sept. 11 attacks in New York, Washington D.C., and Pennsylvania and the 1993 World Trade Center attacks. The waterfalls will be surrounded by hundreds of oak trees on a street-level plaza 1.5 acres wide, meant to shield the space, together with the sound of falling water, from the commercial bustle of the rest of the city.

In conjunction with the memorial, a Davis Brody Bond-designed Memorial Pavilion will sit below ground, with a collection of artifacts from salvaged buildings and personal mementos, and a private room reserved for families of the victims. At bedrock level, the museum will have an exposed section of the 70-ft slurry wall that held the Hudson River, as well as remaining sections of the original foundations. In the center will be a mausoleum with unidentified remains from the attacks. Funding for the $350 million Memorial, unlike the rest of the site, will come in part from 33,800 private donations to the non-profit foundation in charge of its construction and operations.

Key Players

Memorial and Museum Developer: The National September 11 Memorial & Museum Foundation Tower 1 Developer: Port Authority of New York and New Jersey

Developer, Towers, 3 and 4: World Trade Center Properties, a division of Silverstein Properties, Inc., New York Memorial Architect: Michael Arad, New York

Tower 1 Architect: David Childs, Skidmore, Owings & Merrill, New York

Tower 3 Architect: Rogers Stirk Harbour + Partners, London

Tower 4 Architect: Maki & Associates, Tokyo

Architect of Record, Towers 2,3,4: Adamson Associates, Ontario

Geotechnical and Foundation Engineering Services: Mueser Rutledge Consulting Engineers, New York, N.Y.

Structural Engineer on Tower 1 and 3: WSP Cantor Seinuk, New York

Structural Engineer, Tower 4: Leslie E. Robertson Associates, New York

MEP, Towers 1-4: Jaros, Baum & Bolles, New York

Building Envelope Consultant, Towers 1-4: Israel Berger & Associates, LLC, New York

Construction management, Towers 1, 3, 4: Tishman Construction, New York

Steel, Tower 4: DCM Erectors, New York

Concrete, Tower 4: Roger & Sons Concrete, Lagrangeville, New York

Started in late 2008, construction on the Memorial takes precedence as far as scheduling, in order to open in time for the 10-year anniversary of the Sept. 11 attacks next fall. The pools themselves are complex, and heavy-duty. The Memorial will eventually use a total of 8,150 tons of steel — more than the Eiffel Tower, according to PANYNJ — and close to 50,000 cu yds of concrete. Each wall of the pool then requires individual installation of several layers: a waterproofing membrane, a vapor barrier, insulation, followed by the black jet mist granite tiles, of which there are 1,900, installed one at a time by several men. For the water to flow 24/7, 365 days a week, the piping and filter work, going on concurrently, is also substantial as each waterfall will run 40,000 gallons a minute. Underneath all of it, work continues on the Pavilion, which descends 65 feet below ground.

At peak times, the site has 500 workers. The fact that the Memorial is landlocked by all the other projects going up complicates construction – and site access – as does the PATH station underneath the south pool, which, itself, is still under construction while the trains continue to run.

“We’re an island here in the middle,” says Tom O’Connor, the project manager on the memorial project. “Just getting trucks in here is a challenge — security constraints, background checks, the design coordination. We’re literally working right next to each other. The Pavilion is over the station, so I have to build a building over someone else’s steel.”

Then, complicating matters even further, there’s the 12,500-ton chiller plant inside the Pavilion — which has to be connected not only to the museum (“our tropical area,” O’Connor says as we descend the stairs and get hit with a blast of hot, humid air), but also to the Tower 1 retail spaces, the PATH station, Gehry’s Performing Arts Center and the No. 1 train station.

The work is far from hurried, however. During a visit to the site in late June, mock-ups of several different inscription fonts still sit by one of the pools, the team is taking the time to get it right. The mood on the site among the personnel, while more reserved than what one typically finds on a Manhattan project, is friendly and energetic. Most workers smile, and as O’Connor veers among the machinery, foremen stop to shake his hand, ask quick questions, and, eyeing the media presence, share innocent-sounding gossip.

“I’ve always enjoyed construction,” O’Connor says. “The bad part is the politicking.”