Precise. Nodes for the diagrid (left) and megacolumn-superdiagonal connection had extremely tight tolerances. |
(Photos courtesy of Cives Steel Co.)
The Hearst Building leaves no room for error and has "no forgiveness," says Ted Totten, president of Cives Steel Co.s Northern Division. The fabricator, based in Gouverneur, N.Y., furnished and erected the jobs 12,000 tons of structural steel, under a $38-million contract.
Design architect, Foster & Partners, London, wanted the modern tower to appear to float over the six-story, 1928 landmarkto separate the old and new. This forced the general contractor to "approach the project as two separate entities," says Scott Borland, one of three project managers for Turner Construction Co. The New York City builder holds a $252-million guaranteed-maximum-price contract for the core and shell of the 856,000-sq-ft development.
Even with the demands, at 95% completion of the core and shell, the job is on time and under budget, says Borland. And there are no claims, he adds.
Hearst has gone to extremes to consolidate 2,000 employees from 10 locations, and provide a "nurturing, secure" and sustainably correct environment. The owner expects the office building to be the first in New York City to earn a gold rating from the U.S. Green Building Councils LEED program for sustainability. And after the terrorist attacks on the World Trade Center, Hearst beefed up the structure. This included filling "box" megacolumns and superdiagonals with concrete and encasing the steel core in concrete. The curtain wall system also is built to perform better under certain blast conditions.
Work consisted of first gutting the six-story landmarkHearsts headquarters since 1928and then adapting it to function as a hollowed-out lobby-atrium. Concurrently, construction proceeded on the new tower, 160 x 120-ft in plan, that rises from within the 200-ft-square base.
The tower boldly expresses its perimeter structurea diagonal grid pattern of steel, clad in stainless steel. The tower corners "slice" in and out, creating a stack of eight-story, open-mouth "bird beaks." The main entrance, on the east side, leads into a lobby that will contain an $8-million water feature. Sources say the water feature costs more than the plumbing to cool and dehumidify the entire building.
Slicing through the tall water feature are escalators to a third-floor atrium, an open space with ceilings as high as 80 ft that will contain, among other things, Hearsts indoor "piazza." The volume of the lobby-atrium is 1.7 million cu ft.
A clerestory wraps the base of the tower, from floor seven to 10, just above the atrium skylight. The core is offset to the west wall, which abuts a high-rise.
|Rare. Diagrids, free of vertical elements, are efficient but tough to build. (Graphic courtesy of WSP Cantor Seinuk)|
The typical office floor, and the "diagrid," begin at the tenth level. The diagrid is a triangulated system of horizontal rows of steel A-frames. It has no vertical members. A rarity, the diagrid interconnects all four faces of the tower, creating a highly efficient tube structure, says Ahmad Rahimian, president of the projects local structural engineer, WSP Cantor Seinuk.
The intersections, every four stories, of the 57-ft-long legs of the "A"s with horizontal beams form nodes, set on a 40-ft module, that redirect member forces. Architecturally, nodes could not be larger than the cross dimension of the diagrid elements. Gusset plates, though more economical, would have violated the architecture, says the engineer. The architect of record is Adamson Associates, Toronto.
At the "jaw" of each beak, diagrid nodes, typically planar, are three dimensional. To develop the more-complex jaw node, the engineer rejected high-tech methods and built a balsa wood model.
The 10,000-ton diagrid, made of wide flange rolled sections, weighs 20% less than a conventional moment frame, says Rahimian. But its inherent stiffness makes it tougher to build, he adds.
The diagrid transfers loads at the tenth floor into 12, expressed perimeter megacolumns, unbraced for 85 ft. Megacolumns continue to foundations. Eight, 90-ft-long superdiagonals slope in from third-floor megacolumn nodes to column lines at the tenth floor. Superdiagonals carry load and also stabilize the core wall.
A horizontal truss system in the third floor braces the landmark facade, provides diaphragm action for megacolumns and superdiagonals and accommodates the lobby-atrium opening. Tubular steel framing at the seventh floor supports skylight panels and provides lateral bracing for the landmark facade.
On the mechanical side, the building is designed to use 25% less energy than a building that meets minimum requirements of prevailing codes, for a projected savings of 2 million kW hours of electricity per year. Hearst claims the building will reduce stormwater runoff by 30%, through roof rainwater harvesting. The water will be used for landscaping and in cooling tower water makeup. Total water conservation is projected at 1.7 million gallons annually.
The water feature will help cool and dehumidify lobby-atrium air in the summer and humidify the space in winter. "We took an aesthetic feature, and at little cost, integrated it into the mechanical system to maintain comfort and reduce operating costs," says Gary Pomerantz, a senior vice president of the consulting engineer, Flack + Kurtz, New York City.
The lobby-atrium uses radiant heating and cooling, with polyethylene tubing in the topping slab. Office space exhaust air is used to condition the lobby-atrium, which will reclaim energy and minimizes use of outside air.
There was concern about the facade, currently exposed on the interior, and freeze-thaw cycles. To prevent this, the engineer designed a wall-heating system.
For sustainable construction, the team has diverted, to date, 2,419 tons or 84% of waste from landfills, says Hearst. Ventilation systems are protected from...ts an expanded home for the Hearst Corp. media family, not the Hearst family itself. But the Manhattan job may as well be called Hearst Castle East. The builders of the 46-story office buildinga restoration, an adaptive reuse and a modern steel tower rolled into oneare as obsessed with quality and detail as was William Randolph Hearst, when he built his extravagant California estate in the early 1900s.