Glass Act: Where Beauty and Engineering Clearly Meet

Seeing through today's spectacular bolted structural glazing systems to the precision engineering inside
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Sponsored by W & W Glass, LLC
Layne Evans

Clear out to Here: Skylights, Roofs and Canopies

Structural glass is ideal in horizontal applications because it can be engineered to accept very high and complex loads and can be very efficient in terms of heat loss and solar gain. The supports for skylights, roofs, and canopies can be positioned either above or below the steel structure. All overhead glazing must be laminated in order to meet building safety codes, and some codes may require nets in certain applications. To prevent ponding, a 3 degree minimum slope is required. But within these minimal constraints, the sheer transparency of bolted glazing is tailor made for skylights and other designs where maximum openness and clarity are at a premium.

In the Yorkdale project in Canada mentioned earlier, the architects wanted a structureless system for a large span skylight addition, but they also needed the overhead glazing to be strong and safe for the public in the shopping mall below in the face of frequent heavy snow and ice loads.

The 60-foot high, 300-foot long barrel-vaulted atrium was added to the center of the original building built in 1964. The skylight incorporates insulated laminated double glazing that is hung from an exterior structure with gussets supporting seismic fittings. Additionally, it is a showcase for other high technology, as discussed earlier, including ionoplast interlayers and argon gas insulation.

The curved skylight created for the Brooklyn Museum of Art consists of an extremely complex geometric, stepped design. The curved skylight angles downward, with intermediate steps interrupting the roof plain. These vertical glass steps are supported from the interior by an integrated system of steel cables and glass trusses.

At Orlando International Airport the skylights and glass roofs were designed to combine two different types of backup structures. Rather than use steel as a backup, the architects chose to lighten the structure as much as possible. This was accomplished by using laminated glass fins in conjunction with cable trusses located at 11' on center and perpendicular to the fins.

The Imperial Bank Tower Segerstrom located in Costa Mesa, CA involved the design of a 130' long and 20' wide barrel-vault atrium. The biggest concern of the structural glass engineers working on the project was that the glass barrel-vault had to be designed to act as a seismic joint between two very different existing buildings. As a result, the steel and cable tension system needed to be able to support the weight of the glass and allow for movement during a seismic event. New fittings were developed to allow for the extreme movements required by the California Building Code. These custom fittings have since been used on canopies, skylights, and vertical façades in seismically-active areas throughout the world.

The structural glass canopy at the Fox Plaza in Los Angeles was specifically designed to catch glass breaking because of nickel sulfide inclusions and falling from the existing tower above. The canopy was tested for structural and seismic performance, and was designed to withstand the impact of falling glass from 150' in the air. This project serves as a clear reminder of the importance of heat soak testing all tempered glass in point supported structural glazing systems.

Worst Case Scenarios

Structural glazing has been successfully tested and approved for resistance to bomb blast loading. Bomb-resistant structural glazing is typically constructed of insulated laminated double-glazed units. When designing bomb-resistant structural glazing systems, it is important to introduce additional controlled flexibility at the fittings. By understanding the severe deflections that will be induced in the glass during a blast event, the design of the support fittings can be enhanced to achieve significantly greater blast resistance, while from the outside, the fitting can look identical to a conventional support system. Blast-resistant glazing with special seismic fittings was used to create the glass façade of the BBC Television Center in London. Unfortunately, the system had a real-life test when the building was bombed in 2001. Ninety percent of the glazing remained undamaged. In contrast, a large glass curtain wall located about 500' away from the BBC building was severely damaged by the blast.

The Future is Clear

The most advanced current bolted structural glazing systems are lighter, more transparent, more energy efficient, stronger, more resistant to extreme stresses from explosions, hurricanes and earthquakes, and able to fit into more imaginative designs than ever before. Structural glass, when made correctly under tightly controlled conditions, is flatter and clearer than ordinary tempered glass, and options are proliferating in coatings, colors, decorative patterns, high performance, energy efficiency, acoustical, low-iron (for enhanced clarity), solar and even self cleaning glazing. Design innovation has also accelerated in fittings and in supporting structures.

But as will be clear by now, the most important component of the system is knowledge. With the benefits of brilliantly designed and executed structural glazing systems come considerable risks if testing, manufacturing, fabrication and installation are not of the highest order. Liability issues can be especially complex when so many professional teams are involved - project architects and engineers, manufacturers, glass engineers, system designers, testing specialists, skilled fabricators and installers, and many others. The use of a single experienced source bringing together as many services as possible, and offering a single long term system warranty, is one way to effectively manage these risks, and to achieve the integrated approach that marks the most successful - and spectacular - projects to date. With the fundamental factors necessary for long-term safety, performance and beauty ensured, the next generation of bolted structural glazing systems should be even more extraordinary, and even closer to that long-held vision of perfect transparency.

W & W Glass, LLC, is the NY metropolitan area's largest architectural glass and metal contractor. The company is also the largest supplier of structural glass systems throughout the United States. The company exclusively supplies the Pilkington Planarâ„¢ structural glass system. www.wwglass.com

 

 

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Originally published in Architectural Record
Originally published in October 2008

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