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The modern curtain wall has
evolved from static wrapper to active building system.
By Sara Hart
Project manager
Simone Giostra oversaw the development and installation of the
glass, steel, and aluminum curtain wall. (The side and rear facades
are clad in Rheinzink—a zinc, copper, titanium alloy with
highly uniform properties important in facades.) From the beginning,
the challenges were daunting for construction of the entire building.
There was virtually no staging area for equipment and materials.
Deliveries had to be small and precisely timed. With little room
to stage the erection of the facade, Barney Skanska, the concrete
subcontractor, used special forms built on-site. Above the 14th
floor, the contractor switched to a jump-form system from Doka,
an international formwork company. The system is a self-supporting
concrete formwork, anchored to the lower portion of the same concrete
wall under construction. It can be erected without any additional
scaffold or support from the ground.
The south-facing
entrance facade is a complex assemblage of materials—high-strength
concrete, architectural concrete, aluminum and glass fenestration,
and steel cross bracing. The architectural concrete (8,000 psi)
was to be visible through the curtain wall, so the interface between
panel and concrete was critical.
The fabrication
and installation of the south facade was plagued by what can only
be described as a clash of building cultures. The facade’s
glazed panel system was fabricated by an Austrian company called
GIG Fassadenbau GmbH, but the structure on which the curtain wall
was to hang was built to American standards. “In Europe,
the tolerances are much tighter than in the U.S.,” Giostra
explains. “Whereas the panels were designed with a tolerance
of 3¼16 of an inch, the concrete structure allowed for
as much as 1-inch variance.” Furthermore, the design called
for the architectural concrete to be visible through the curtain
wall, precluding any workable but visually unacceptable solutions.
Because of the discrepancy, the brackets connecting the curtain-wall
panels to the concrete superstructure required a survey of the
entire south elevation and fabrication of new steel brackets,
which could absorb much wider concrete deviations.
It has been
described as a puzzle by the engineers, the contractors, and the
construction manager. It might be more like building a ship in
a bottle, fashioned with European precision and American perseverance.
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