The building team for the eight-acre urban park of the $700-million National September 11 Memorial & Museum—the emotional focal point of the $19-billion World Trade Center redevelopment in Lower Manhattan—is obsessed with something as mundane as surfaces: ground, water, stone and metal.
But the team has a huge burden on its shoulders, one that goes deep down. In the hubbub of activity at the 16-acre WTC site, crews have to deliver 80% of the structured park—a giant green roof topping the site's five-level basement— in pristine condition for the looming Sept. 11 ceremonies marking the 10th anniversary of 9/11.
The memorial team is giving extra-special care to the heart and soul of the project: the 2,983 names of the 9/11 victims etched into the surface of bronze-covered parapets bordering each of the memorial's pools. The pools—each of which is 31,264 sq ft and contains 485,919 gallons of water—are set into the footprints of the original 110-story Twin Towers, destroyed by the terrorists.
While each pool has a pumping system powerful enough to recycle 52,000 gallons of water per minute, it is the surface of the nearly 1,600 lineal ft of parapets that had to be robust enough to withstand rain, scorching heat, snow and ice as well as the wear and tear of three million annual visitors. For the comfort of the millions of hands that will touch the etchings, the parapets have a heating and cooling system.
"The [National September 11 Memorial & Museum non-profit foundation] was very concerned about making the experience as pleasurable as possible for visitors," many of whom will want to touch the engraved names, says Robert Downward, an associate with the project's local MEP engineer, Jaros Baum & Bolles.
JBB and Service Metal Fabricating, the parapet's Rockaway, N.J.-based supplier, knew of no prototype for a project like this, so they started from scratch to build a back-mounted tubing system that would work within the parapets and the nameplate system. The fabricator built a prototype of the panel, tested it under sunlight and then analyzed the results using computational fluid dynamics modeling.
"We calibrated the model so that it produced results in line with real field conditions," Downward says.
The result is a network of tubes that feed water behind the bronze plates. The tubes, nearly camouflaged, are underneath the plates and parallel to the rows of names.
"The spacing between the tubes was critical to maintaining comfortable temperatures at the panel surface," Downward says.
Each parapet section was shipped to the site with the tubes attached. Then, using a series of manifolds, workers connected the tube sections to the piping. The piping is connected to below-grade equipment that supplies the heated or chilled water.
With all 152 parapet sections installed, crews should be finishing up backlighting by Aug. 20, says Kevin P. Murphy, project executive for construction manager Lend Lease, formerly known as Bovis Lend Lease.
The memorial, at the site's plaza level, is a green roof that covers the 185,000-sq-ft subterranean museum as well as the PATH commuter rail line from New Jersey. More than 400 swamp white-oak trees—each nearly one ton—surround the pools. The memorial's designers are local architect Michael Arad and landscape architect Peter Walker, Berkeley, Calif. (ENR 1/12/04 p. 7).
When completed, the memorial and museum will contain 8,151 tons of steel and about 49,900 cu yd of concrete, according to the WTC landowner, the Port Authority of New York & New Jersey.
About a year ago, New York City Mayor Michael Bloomberg, the chairman of the foundation's board of directors, decided to open the "Reflecting Absence" memorial plaza to commemorate the 10th anniversary of the 9/11 attacks. That decision jolted the memorial team into overdrive. Some 525 workers from about 50 firms have been putting in 12-hour days, seven days a week, since last August to finish 80% of the park, says Salvatore Adinolfi, executive vice president of design and construction for the foundation, which is charged with developing the project. Completion is set for September 2012, after work on the other WTC projects is further along.
