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Technical Resources One North Wacker Drive: Anatomy of a Glass Building New structure breaks ground in the use of glass By Jenni Rothrock An eclectic mix of architecture occupies the "loop area" of Chicago's downtown business district, mingling the art deco and French Renaissance style of the Civic Opera House (1929) with the classic spires of Saint Patrick's Church (1852) and towering facades of postmodern skyscrapers. Each building is a testament to the time period in which it was built, and the new One North Wacker Drive building is no different. The area's first multi-tenant office building to be built in the 21st century, the structure features cutting edge glass and glazing systems reflecting today's technological progress. Standing 54 stories tall, the building is divided into four zones, varying in size. Its most unique feature is the ground floor lobby, which is constructed using an innovative net wall glazing system designed by Advanced Structures, Inc. (ASI) of Tenafly, NJ. Developed in Germany and first used in Munich's Kempinski Hotel, the system is composed of 3/4-inch pretensioned cast stainless steel cables that hold 5 by 5 foot glass panels made of Schott Corp.'s water white, non-reflective glass coated with Amiran, a special non-reflective coating. The panels are attached to the cable system using stainless steel glazing buttons. There are no mullions to speak of. Seven bays, 30 feet wide and 40 feet high, each constructed using the net wall glazing system, make up the south walls of the lobby. The east and west lobby entrance facades are also constructed with the net wall system, with each wall measuring 45 feet wide and 40 feet tall. The result is a completely transparent lobby, which, as architect Steve Nilles, Lohan Associates, Chicago, explains was an essential part of the building's design. Originally, the John Buck Co., one of Chicago's leading developers and orchestrator of the project, suggested the building's base be clad with stone. Nilles points out that because it's undesirable, architecturally, to apply a stone base to a modern curtainwall tower, the challenge was to create a lobby that conveyed the presence and quality of stone, without actually using it as a base. Because of the net wall's transparency, the passerby is drawn to the lobby's interior core wall, which is clad in blue Orissa granite imported from India and Italian Carrara marble. "It is truly transparent so that on the pedestrian level you can see through it and actually become part of the lobby from the exterior," explains Nilles. "The non-reflective coating of the glass adds to the system's transparency, which further breaks down the barrier between interior and exterior, making the interior's stone cladding really part of the building's base," he continues. Innovative plaza elements designed by landscape architect Peter Walker, border the building entrances, complementing the stone cladding and completing the effect. One North Wacker Drive is the first building in the United States to use the net wall system, a fact that was not without its challenges. Bob Trainor, president of Trainor Glass Co., Allsip, IL., the glazing contractor for the project, points out that selling the net wall concept was a challenge in and of itself. "It took over a year from the time we started promoting the net wall system to the time we got the job," he explains. "The concept of the net wall system is just so new to the United States," he emphasizes. Particularly challenging to the building designers was the system's allowable movement. Net wall designer Franz Safford, a principal of ASI, explains, "Traditional walls have a deflection value equaling the span of the wall divided by 175. The cable net wall is a high deflecting structure with a maximum deflection value equaling the span of the wall divided by 50." The challenge, as Safford explains, was to integrate fixed door assemblies into the high deflecting system. Each component of the system is tested and designed to accommodate the deflection, including the glazing, glazing buttons, glass, and cables. The door assemblies, however, required some creative engineering. As a solution, the lobby entrances are set in a pin-connected structural steel portal attached to the net wall. A tapered, stainless steel clad frame then surrounds the lobby's structural glass revolving and balanced doors, providing an air and water seal between the fixed door assemblies, which remain stationary. Nilles points out that cooperation between the architect, structural engineer, net wall designer, and glazing contractor is essential in making a system of this caliber work. Crane Revolving Doors, which provided the structural glass revolving doors, and Ellison, which provided the structural glass balanced doors, were also involved in the design process. "Because of the pretensioning of the system's cables, a good deal of design has to take place early on to accommodate the tensioning loads of the cable system into the superstructure of the building," Nilles explains. The Tower The remaining 52 stories of the building are clad with a unitized, structural silicone glazed, pressure-equalized aluminum and glass curtainwall. As Nilles explains, the developer wanted the building to be very modern in its appearance, reflecting the state-of-the-art technology of its tenants. To create this look, the building's insulating vision glass units use Viracon's blue/gray low-E coating VE1-52 on the #2 surface. Panels using a spandrel glass in a custom blue/gray color with a ceramic coating complement the units. In contrast, recess bays are clad with metallic three-coat finished aluminum panels. To complete the effect, the two-floor supergrid on the building's north and south elevations, as well as the structure's round column enclosures, are clad with Avesta Sheffield's high clad linen patterned stainless steel, which Nilles explains, "imparts a very soft, radiant glow." "These profiled and curved patterned stainless steel panels combined with Viracon's blue/gray glass provide a dynamic mix of color and diffuse reflections, resulting in a very modern skin," points out Nilles, adding that the shading coefficient and R-value of the Viracon units allow for an energy efficient building envelope. A modern appearance was not the only characteristic required by the John Buck Co., however. The developer also wanted the tower to be able to accommodate tenants with a variety of office space requirements. As a result, the tower itself is a "stepped" structure, with three different floor sizes of 38,000 square feet, 33,000 square feet, and 29,000 square feet. Nilles explains that the idea was to split the building into zones to accommodate tenants with varying needs. Beauty in Design While the building's exterior reflects the fast-paced, technologically advanced state of today's business world, the interior offers occupants a haven from its rapid pace with a beautiful, soothing design. Glass plays an important part in creating this atmosphere, points out Nilles. To complement the light-filled, nature-inspired look of the lobby and landscaped plaza, he used a luminous "floating" glass ceiling in its elevator vestibule. A suspended aluminum plate grid with a point-supported open joint glazing system creates the illusion of a floating ceiling. Panels within the aluminum grid actually "open up," as Trainor describes, allowing access to lighting fixtures requiring maintenance or cleaning. Made of S.A. Bendheim's patterned glass laminated to a water white tempered top lite with a translucent interlayer, the ceiling complements the white Carrara marble of the lobby. The result-a calming, cool atmosphere offering tenants a reprieve from the harried outside world. Perhaps one of the most intriguing aspects of the building's interior is its elevator cabs, which are made entirely of curved, laminated point-supported water white, low-iron glass provided by Goldray. The glass is composed of multiple layers, each featuring a different fritted pattern, with the #4 surface coated with a metallic accent, color flood coat. Each of the cabs is of a different color, explains Nilles. Furthering the unique effect are halogen light sources in the ceiling of each elevator that shine through the luminous glass ceilings. "The cabs are a little out of the ordinary," Nilles admits. However, "the different patterns of the multiple layers of glass, combined with the halogen light sources, create an interesting depth and shadow for each elevator," he points out. The innovative use of glass can be found throughout the building, even down to the restroom design. Rather than using traditional stone lavatory counters, Nilles opted to use an all-glass design featuring free-floating, curved and profiled tempered glass. Provided by Goldray, the glass features a transparent patterned ceramic frit on its underside surface, and stainless steel bowls are inset into each 9 foot long counter. To create the illusion of a floating countertop, the glass is supported by stainless steel brackets, and does not actually touch any of the wall surfaces. The newest entrant in Chicago's downtown business district, One North Wacker Drive is the 21st century's first addition to the loop area's architectural timeline. Expected to be complete in June of 2001, the structure truly serves as a historical marker for its time period, representing the future of glass and glazing in the 21st century. Source: Appeared in Glass Guide for Architects, Glass Magazine June 2000. |
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