A bridge of strength

The three-year, $120 million Chattanooga waterfront redevelopment project was an ambitious one [Figure 5]. The plan called for a joining together of the Hunter Museum of Art, the Tennessee Aquarium and a new spacious riverside park, creating a desirable and functional recreational area. Although the Hunter Museum is only three blocks from the Aquarium, steep steps and narrow streets had made the area inaccessible to many and daunting to most.

What was needed was clearly an elegant pedestrian bridge to link the different areas. The result was Holmberg Pedestrian Bridge, a 200-foot-long glass structure that incorporates the themes of both art and the waterside location, all 50 feet above traffic.

"We were challenged to create a bridge that complemented the existing Walnut Street Bridge-a historic steel truss walkway that led pedestrians to the river-but also one that was a sculpture on its own," said Ray Boaz, partner in the Chattanooga firm Derthick Henley & Wilkerson Architects. "Therefore, we needed to make the bridge as thin and open as possible to maximize views and that's where glass came into play." According to Boaz, the material was eagerly accepted by the client, the City of Chattanooga. The added challenge -a glass bridge-was a first for the firm and the city.

Yorkdale Mall, Toronto, Canada The structural interlayer promotes good edge stability, enabling the laminated glass to bear heavier loads. Architect: MMC International Architects Ltd., Toronto Photo credit: Chris Brown, MMC International Architects

In order to determine the proper structural tolerances, the design team worked closely with interlayer specialists to effectively provide the proper support without over-designing the project. The final product supports more than 300 people and features two distinct finishes that allow pedestrians to chose their path-either a translucent one that obscures the traffic below or a transparent path that provides an experience of walking on air. The walking surface has been treated with a textured traction layer to assure that it is skid-proof and safe.

"It was a lot easier than I thought it would be," said Boaz, who used a new strength calculator (below) to determine the maximum glass stress under load, laminate deflection, effective laminate thickness and time and temperature behavior for the bridge.

Boaz advises other architects to work closely with both their structural engineer and interlayer manufacturers. "Once you understand the tolerances and characteristics, working with the glass isn't a whole lot different than working with any other material. Jump into it-it has a lot of exciting possibilities," he said.

Holmberg Pedestrian Bridge, Chattanooga, Tennessee The use of laminated glass with advanced polymer interlayers allowed strength and transparency in this key waterfront redevelopment project. Architect: Derthick Henley & Wilkerson Architects, Chattanooga Photo Joe Hailey, Ross Glass

Clearly, laminated glass has come a long way since that French chemist knocked over a bottle and saw the cohesive benefits of the substance that would become known as the interlayer-first PVB, and now advanced polymer interlayers that extend and enhance performance. Laminated glass can now be stronger, thinner, and more transparent than, scientists could have imagined only a few decades ago. As more design professionals investigate the uses of laminated glass with advanced polymer interlayers or structural interlayers, innovation and new applications are certain to follow.

Glass Laminating Solutions Operating worldwide, DuPont Glass Laminating Solutions, E.I. du Pont de Nemours and Company provides improved personal safety, property protection, public security, energy efficiency and sustainable development through the use of laminated safety glass. From storm protection to life-saving accident and injury prevention, science-based products and services from DuPont Glass Laminating Solutions are helping people everywhere enjoy safer, healthier, more comfortable lives, while conserving energy and enjoying the view. DuPont was a founding company involved in the development of the laminated safety glass industry and remains a leading innovator in this field, offering the world's broadest range of traditional and specialty-performance interlayer technologies.