Landmark Pedestrian Bridge

by Marcy Marro | March 2, 2020 12:00 am

Luke A. Volkmar, AIA, CDT, LEED AP BD +C, architect at Neighboring Concepts, says the bridge marks the transition of suburban to urban context. “The client requested an iconic architectural design that signified the entrance into the City of Charlotte, as a passenger travels the light rail train into Uptown Charlotte,” he says. “The transparency of the bridge and towers allowed the design to use material and light to mark a gateway into the city while also making the structure open and welcoming, ensuring passengers feel safe throughout their transit experience. Lastly, the client required minimal maintenance for the structure, given its challenging site location and operation schedule of the various railroad and train agencies the bridge is spanning.”

To meet the project requirements of openness and weather protection, while providing the flexibility and strength required for the methods of installation in the field, the architects chose a metal façade system. The North Carolina Building Code required the bridge’s perimeter walls to be at least 50% open, since a fire sprinkler system was not available due to the challenging project site. Volkmar says this requirement was in direct conflict with the city’s requirement of weather protection, ensuring transit patrons would have a safe, weather-protected path of travel. Therefore, the design team created a dual-layer perforated metal wall assembly to meet the requirements.

“The dual layer assembly provides the exterior wall openness that was required by building code, while providing protection from the weather,” Volkmar explains. “The outer layer of smaller, but more frequent openings serves as the initial protection from the elements. A 2-inch center drainage plane separates the two layers, while a secondary layer of larger, but less frequent openings serves as the second layer of protection. The dual layers serving this functional purpose were then taken advantage of to design the signage element on the bridge.”

For the project, McNICHOLS Co.,[1] Tampa, Fla., supplied 5,000 square feet of two types of aluminum perforated metal panels, which were combined in a dual-layer assembly. The upper outer layer, which provides increased weather protection while meeting openness requirements for the structure, was created with McNICHOLS 68% open, 0.063-gauge perforated metal panels with 1/4-inch by 1 1/2-inch rectangular slots. The inner layer is McNICHOLS Airline Panel, a 58% open, 0.125-gauge perforated metal panel that serves as a drainage plane as well as fall protection, as it’s exposed directly to pedestrian traffic over the rail line. All of the panels were finished with a two-coat PVDF, Kynar 500 finish. Additionally, East Coast Metal Systems Inc.,[2] Triadelphia, W.Va., supplied Larsen aluminum composite panels[3] by Alucoil North America[4], Manning, S.C., for the bridge coping, soffit and stair tower elements.

Volkmar says that building a bridge spanning an active freight and light rail transit line required special considerations and detailing methods. The entire bridge was fabricated adjacent to the rail lines, and set in place with a single pick of a crane. Messer Construction Co.[5], Cincinnati, was provided three-hour windows at separate intervals for all work taking place within the railroad right of ways, including setting and placing the bridge, façade and roofing scope. Materials were prefabricated off-site, with larger assemblies of prefabricated elements assembled adjacent to the right of way for ease of installation during the windows.

“The greatest feat was the mobilization and setting of the bridge truss,” Volkmar says, “which required an 800-ton crane to pick and set the bridge in a single movement during a three-hour window.”

Volkmar adds the project was required to meet Buy America requirements, meaning all materials had to be fabricated and assembled in the United States. “Working with a domestic manufacturer was critical in meeting this requirement,” he says, “and helped facilitate additional coordination during shop drawing detailing to ensure the installed product would meet the installation and final design goals necessary.”

Source URL: https://www.metalarchitecture.com/articles/landmark-pedestrian-bridge/

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