Hanging out

Suspended glass offers aesthetics, advantages
By Terry Peterson
May 1, 2007
COMMERCIAL, RETAIL, FABRICATION : PROJECTS

Floating limitlessly above heads, the glass seems to extend past its steel perimeter. It glows in the light and shields passers-by from nature’s elements. This innovative approach to canopies is quickly catching the attention of architects worldwide.

Glass has become one of the architectural designer’s “go to” tools for accomplishing artistic expression. When a building’s entryway is image-critical, it makes perfect sense to get one of the highest quality material components physically close to the visitor, creating a positive first impression. The desire to create a first-class entrance has led designers to consider suspended glass on canopies used in the commercial construction marketplace.

While enhanced aesthetics is an obvious advantage with suspended glass, the design offers many additional benefits. Recent projects utilizing the suspended glass approach have experienced fantastic advantages—as well as technical challenges—and require the expertise of a knowledgeable team of architects or designers and specialty glazed structure professionals.
Westin Crown Center, Kansas City, Mo.
Advantages of suspended glass
A suspended glass approach in a canopy places the glass below its steel structure, eliminating the need to penetrate the glass when tab attachments are needed. This approach makes the process less expensive and offers easier sealing to prevent leaks. Glass suspended using point fixings has to be designed structurally. It has to be laminated to meet safety codes and heat strengthened to perform in a structural way. To reduce the impact of dirt, sometimes a light dot pattern of ceramic frit is utilized. If more opacity is desired, a colored interlayer—usually milky white—can be used. The resistance of interlayers to the environment has improved greatly and polyvinyl butyral material such as Saflex, manufactured by Solutia Inc. of St. Louis, perform well even when the edges of the glass are fully exposed to the elements. Domestic glass fabricators have shied away from suspended glazing but there are many sources throughout Europe, such as Saint-Gobain of France and BGT Bischoff Glastechnik AG of Germany, who have successfully supplied the material for a number of years.

Glass as a building material can be designed structurally. It is a matter of applying the mechanics of the material made available through testing, and then applying engineering principles to determine the glass layup—glass thicknesses and interlayer—in resolving the loads and span requirements.

Novum Structures, a specialty contractor for high-technology spatial architectural structures and enclosures, has engineered and executed several suspended glass canopy projects.

Novum recently worked with Hellmuth, Obata + Kassabaum Chicago to create a clean, modern, curved entry canopy for SpringHill Suites, Chicago. The teams conquered challenges including sourcing curved structural glass economically and keeping the overall canopy within budget. When tackling the technically challenging canopy, it helped to have a single-source provider to simplify the process.

“We chose Novum because they can provide the glass, the engineering, the metal and the actual installation of [projects] of this nature,” says Nimrod Gutman, an architect/designer at HOK Chicago who worked on the SpringHill Suites project.

More value can be added with this revolutionary design concept when the architect engages the canopy provider at the project’s earliest stages. “In providing a single source from engineering through construction for the glass, supporting steel and drainage system, we not only guarantee the budget at the earliest stages, but work collaboratively with the architect on detailing decisions through CD development to ensure all cost goals are met,” says Ian Collins, president of Novum Structures LLC.

Suspended glass creates another benefit because the glass is used as a “floor” instead of a “roof,” significantly reducing the canopy’s attractiveness to birds as a possible habitat or nesting site. Placing the lightweight steel support on top with no cover virtually eliminates protection for feathered friends from natural elements including rain, sun and wind.

Simplified and higher quality detailing is another positive result for the architect when the glass is moved down under. The Novum Point Supported Glass System grabs the glass at a point, making drainage easier by eliminating bulky aluminum mullions associated with conventional metal-framed skylights. The system allows for free flow of water and reduces maintenance.

“[Novum] was innovative in [its] approach to putting the steel structure together that holds the glass,” says David Murray, of Odell Architects, Charlotte, N.C., who worked with Novum on creating a suspended glass canopy for Greenville Memorial Hospital in Greenville, S.C. After the initial suspended glass canopy was completed, the approach and structure was carried out throughout the entire Greenville Memorial Medical Campus.

Technical challenges
One of the advantages of suspending the glass is to simplify and improve detailing, but from an engineering standpoint, it is technically challenging. The suspended glass must have a structural design, and specially constructed point-supported glass fittings, with adequate bearing surface to keep stresses in the glazing within allowable limits.

“Like the steel that supports it, the glazing becomes a structural element that must be engineered using proprietary Finite Element Analysis computer programs,” says Soeren Stephan, director of engineering at Novum Structures.

In addition, steel tolerances have to be better than the guidelines permitted by the American Institute of Steel Construction, Chicago. This is best accomplished using hidden mechanical connections in the structure while eliminating welding. Similarly, gutter or drainage design is not straightforward and requires a well-calculated plan by an experienced engineer.
Consolidated car rental, Fort Lauderdale-Hollywood International Airport
Architects at Spillis Candela DMJM, Coral Gables, Fla., faced the challenge of creating an entranceway canopy design at the Fort Lauderdale-Hollywood International Airport that would impress travelers at the ground level and also on the second and third levels, where the top of the canopy can be viewed.

“We had some significant nervousness, on the part of the airport, about seeing dirt or leaves through the glass,” says Michael Kerwin, principal and chief designer at Spillis Candela DMJM. “The intention was to provide as smooth and sleek of a surface on the upper level as possible, so that water, leaves, birds or animals would find it relatively hard to stick to that area.” Kerwin says he has not heard of any issues related to any bird nesting problems on the canopy.

The 510-foot-long suspended glass canopy at Fort Lauderdale-Hollywood International Airport is on the busy north side of the building, which experiences the traffic of buses, rental cars and pedestrians. 

The proposed solution originally included metal-framed skylights and welded-up heavy steel. The project designers developed the original design with separate consultation from vendors on the steel and the glass. Novum recognized possible performance issues with the proposed design and pursued a single-source strategy that would more optimally integrate the steel and glass. A much lighter, prefinished space frame structure, Novum KK-System, was selected in combination with suspended point-supported glass, Novum PSG-System. The resulting solution provided enhanced performance, looked better and cost less.

Technical challenges weren’t the only factors considered when Kerwin’s team decided to use suspended glass. More than 1 million travelers pass through the entranceway each year. With such high traffic, Kerwin knew the canopy had to be aesthetically pleasing and make a definite statement.

“We kept getting questioned, ‘Why does it need to be glass?’ ” Kerwin says. “We wanted to prove that there was value in the transparency of the glass canopy and in raising the level of technology at the entranceway. As you approach the building, you don’t create darkness right at the front door. You get light down through [the canopy], adding to the high-technology, progressive appearance of the building.”

 

 

Sources:
Nimrod Gutman
Architect/designer
HOK Chicago
30 W. Monroe St.
Chicago, IL 60603
312/782-1000

Ian Collins
President
Novum Structures LLC
W126 N8585 Westbrook Crossing
Menomonee Falls, WI 53051
262/255-5561

David Murray
Principal
Odell & Associates
800 W. Hill St.
Third Floor
Charlotte, NC 28208
704/414-1000

Soeren Stephan
Director of Engineering
Novum
W126 N8585 Westbrook Crossing
Menomonee Falls, WI 53051
262/255-5561

Michael Kerwin
Principal/chief designer
Spillis Candela DMJM
800 Douglas Entrance
North Tower, 2nd Floor
Coral Gables, FL 33134
305/444-4691

 

The author is vice president of sales for Novum Structures, Menomonee Falls, Wis., 262/255-5561, terry.peterson@novumstructures.com.