Wind forces. Most skyscrapers have an impermeable envelope. This building project is unusual because both the arcade at grade level and the copper-clad roof are open to wind forces on the interior walls, says Nicholas Isyumov, research director at the University of Western Ontario's Boundary Layer Wind Tunnel Laboratory, in London, Ontario.
Round dormers that let air in and out through copper grilles are located at the top and the bottom of the 150-ft-high roof space, creating a four-story-high plenum. Bottom dormers at the 50th floor level have an air intake through cooling towers located at the 708-ft to 731-ft levels. The air is exhausted through the dormers at the top of the roof. All of the dormers are in a vertical position to reduce the chance of water intake. Mechanical-electrical design is by Cosentini Associates, New York City.
The actual wind loads on the building will be higher than they are on some nearby skyscrapers because it is "away from the built-up parches of Manhattan. It does not have the sheltering effect of surrounding buildings and the biggest, strongest winds in Manhattan tend to come from the west," says Isyumov. To the west of the project, most of the surrounding buildings are five-story walk-up tenements.
The roof structure, used as a penthouse for the mechanical equipment, is made of prefabricated copper panels. HRH suggested that the roof be panelizes so it could be installed like a curtain wall and scaffolding would not be needed for its erection. As results, the roof was built from the interior "with as few pieces as possible," says SOM's Rowe. The 2 x 26-ft-long copper sheets were lifted by crane and derrick, adds Peter M. Chorman, SOM's assistant project manager for the roof and arcade. They were stored on the 47th floor and on the two floors inside the roof. Subcontractor Werner Dahnz, Toronto, designed and fabricated the copper roof panels. They are made of girts with ribs "similar to curtain wall mullions that span between the girts, " says Rowe. The girts are being bolted in the field to sloping columns. The copper roof panels had to be equipped with doors to provide access to the lighting equipment that will be used to illuminate the roof.
Rowe adds that SOM typically specifies that a portion of a window wall be tested for wind loads air infiltration. Here, in addition to a section of a wall, a section of the roof with dormers also was built and tested. "The first time it failed miserably. The copper loosened up in the first test," explains Rowe. The problem was corrected by increasing the bolt size and reducing the bolt spacing from 18 to about 12 in. on center. The copper panels, with copper stiffeners on 8-in. centers, are held between aluminum glazing stops that are bolted to aluminum mullions. A gasket separates the two dissimilar metals. At the top of the copper-clad roof is a pyramid space frame clad with translucent glass.
The grade-level plaza, located between the residential and commercial towers, is reached directly from the arcade. Its construction was a priority because its open area was needed for the storage of construction materials on the tight midtown site. The plaza also is being used as a staging area for the fabrication of reinforced concrete sections for the residential tower and the townhouses. But before the structure supporting the plaza's landscaping, fountain and vehicular drive could be built, the project's six theaters had to be constructed.
The roof of the theaters is at the bottom of the tree wells, says Michael Sardina, principal designer for the landscape architect, The SWA Group, Boston. Loading is the 10-ft-wide vehicular drive that is adjacent to the commercial tower.
To support the plaza weight and get the necessary clear spans for the theaters, four 7 ½ -ft-deep girders frame parts of the underground structure. Two of the deep girders are 80ft long and two are 60ft long. The heaviest of them weigh 784 Ib. per ft.
The plaza will have trees, shrubs and "a substantial amount of seating," says Sardina. Two 30-ft-high pavilions one on either side of the plaza, will provide entrances to the underground theaters as well as retail space on the plaza. To attract pedestrians and keep the public spaces active at night, the commercial tower will be washed with lights. The rooftop pyramid, lit from within, will become a beacon on the city's skyline.
14. Answer the questions to part V:
1. What envelope do most skyscrapers have?
2. Why is this project unusual?
3. What is creating a four-story plenum?
4. Where is the air intake at the 50th floor?
5. How is the air exhausted?
6. Why are all the dormers in a vertical position?
7. Why are the actual wind loads on the building higher than on nearby skyscrapers?
8. Where do the biggest winds in Manhattan tend to come from?
9. Is the roof structure used as a penthouse for residents?
10. Why wasn’t scaffolding used for the roof construction?
11. What mechanisms were used to lift copper sheets?
12. Who designed and fabricated the copper roof panels?
13. How is the access to the lighting equipment provided?
14. What was tested for wind loads and air filtration?
15. How are the copper panels held?
16. What is reached directly from the arcade?
17. What was another function of the plaza?
18. What was necessary to construct before the fountain and vehicular drive?
19. Where is the roof of the theatres?
20. What frame parts of the underground structure?
21. What will the plaza have?
22. What do the 30-ft-high pavilions provide?
23. Why will the commercial tower be washed with lights?
24. What will the roof-top pyramid become?