Answer the questions to part IV:
1. Who is the project engineer for the commercial tower?
2. Does all of the core bracing continue to the top of the building?
3. What was needed to transfer the wind loads around the corners of the building?
4. What columns were used between the 11-ft-wide bays?
5. What welding was used for the horizontal stubs?
6. What company fabricated the structural steel?
7. What needed field welding?
8. What is the steel framing compared to?
9. What load do the 18 floors of the framing carry?
10. How high is the curved masonry?
11. How does the floor area vary?
Read part V and answer the questions after it. Make sure you can explain the following terms and word combinations from part V.
Impermeable envelope Wind forces Research director Wind tunnel Boundary layer Round dormers Roof space A four-store-high plenum Air intake Exhausted air Water intake Wind loads Built-up patches Sheltering effect Penthouse Panelized roof Curtain wall Scaffolding Crane Derrick Assistant project manager Subcontractor
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Mullions To span between the girts To specify Loosened up copper The bolt spacing Copper stiffeners Gasket Translucent glass Tight midtown site Staging area Plaza’s landscaping Vehicular drive Tree wells Principal designer Landscape architect To frame parts of the structure Substantial amount of seating Pavilion(s) Retail space To wash with lights Lit from within
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Part
V. 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 a
re
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 locate d 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.