New 7 World Trade Center Uses Type 316 Stainless Steel
By Catherine Houska, TMR Stainless (Consultants to IMOA)
The original 7 World Trade Center building consisted of an office tower, electrical transformer vaults and access ramps to the World Trade Center’s service levels. Like the twin towers across the street , this 47-story building completely collapsed as a result of the events of September 2001. Immediate reconstruction was required, primarily due to the need to rebuild Manhattan’s power grid.
As the first building constructed on the site, it will be highly visible. The architects, Skidmore, Owings & Merrill (SOM), were challenged by the owner, Silverstein Properties, to improve upon the original building’s function and appearance.
The building is currently under construction. The first 26 meters (85 feet) of the office tower will contain the Con Edison electrical transformer vaults, which require a significant amount of ventilation. Offices will occupy the higher floors of the building. Because it will function as both an industrial facility and an office building, there were unique design challenges.
The stainless steel and glass exterior surfaces were designed in collaboration with artist James Carpenter. Molybdenum-containing Type 316 stainless steel was selected, because the building will be exposed to both coastal and deicing salt and moderate levels of urban pollution. The owner desired a building that would remain attractive over time and provide a long service life. Molybdenum alloying additions increase a stainless steel’s resistance to corrosion and staining by salt and pollution.
SOM’s rendering of the new
7 World Trade Center.
SOM and James Carpenter used the different purposes of the upper and lower building to create a study in reflected color, light, and depth, which will add a sculptural element to the building. The exterior of the office tower on the upper floors will be comprised of floor-to-ceiling clear glass with concave, Type 316 spandrel panels between the floors. The spandrel panels will be embossed with a light pattern that simulates abrasive blasting and then corrugated. The horizontal corrugation pattern will enhance light reflection. Below each panel there will be a horizontal sill made of blue, electrochemically colored, Type 316. The blue color will reflect onto the concave spandrel panels giving them bright, bands of reflected color. The owner plans to wash the stainless steel panels when the windows are washed to prevent dirt and salt accumulation.
A rendering of the spandrel and blue-colored Type 316 panels that will be used between each floor in the office tower.
Placement of the blue panels was determined by varying the panel angle
relative to the spandrel to obtain optimal reflection onto the spandrel
panels.
The exterior walls surrounding the transformer vaults have to accommodate high airflow requirements. Welded Type 316 mesh was selected. Woven mesh was not considered, because there are tiny crevices at each point where wires cross and Type 316 can be susceptible to crevice corrosion when exposed to salt.
The exterior walls surrounding the transformer vaults have to accommodate high airflow requirements. Welded Type 316 mesh was selected. Woven mesh was not considered, because there are tiny crevices at each point where wires cross and Type 316 can be susceptible to crevice corrosion when exposed to salt.
Welded mesh had previously been used only in industrial locations, so SOM and Johnson Screens created a more aesthetically pleasing product. By using custom triangular wire profiles, by changing wire orientation and finish, and by varying wire density, a surface with varying reflectivity was used to create depth, surface variation, and visual interest. The two layers of Type 316 stainless steel wires are separated by a 165 mm (6.5 inch) cavity. The inner layer is lit at night with blue and white LED sources. The color is programmed to shift in color tone from day to night and the surrounding surface pulses and moves subtly through the night because of the wire profiles and their orientation. The welded mesh will also be cleaned on a regular basis.
Day (left) and evening (right) views of
the welded mesh encircling the bottom
26 meters (85 feet) of the tower.
Light and color variation was obtained
by varying the wire shapes and their
orientation within the welded mesh.
