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Tensile fabric structure transforms Denver Union Station

December 1st, 2014 / By: / Case Studies, Feature

Shade, weather and beauty solutions for the commuters of Denver’s urban core.

Denver, Colorado’s Union Station is an integral part of the Mile-High City’s vibrant urban core. The centralized transportation platform opened for business in 1881 and has become a hub for the city’s travelers and commuters. It currently facilitates travel via Amtrak train and three urban light rail trains, as well as citywide bus service. In 2009, the city began a $500 million renovation on the facility, including roofing of the massive train hall and several transit waiting stations.

Engineers and designers on the renovation team turned to industrial fabrics to create roofing solutions for the facility’s train hall and Amtrak and light rail waiting stations. Tensile and fabric structure designer, manufacturer and installer Structurflex, Kansas City, Mo., was asked to join the project team to design and deliver a vast membrane roof for the train hall structure and canopies for waiting and drop-off areas within the station.

The Structurflex team joined architects from SOM, engineers, steel fabricators, contractors and steel erectors to create eight unique tensile fabric structures for commuter rail, Amtrak, light rail and bus terminal applications spread over 1.35 million square feet of mixed-use development and civic space.

Fabric follows function

Project leaders decided on Sheerfill II for the train hall roof, and Sheerfill V for the light rail waiting canopies. Both Sheerfill products are polytetrafluoroethylene (PTFE) coated fiberglass fabrics produced by Saint Gobain of Paris, France. A single layer ETFE system was used for the Amtrak station canopies. PTFE has many industrial uses, including electrical insulation, computer components, and machinery lubrication. Its versatility, hydrophobic qualities, and safety rating make it useful as an industrial roofing fabric, as well. Perhaps most notably, Minneapolis, Minnesota’s former Hubert H. Humphrey Metrodome used more than 20-acres of the material for its double-sided fabric roof. Denver International Airport’s main terminal roof is also covered with PTFE.

The station’s massive train hall canopy, the centerpiece of the renovation, stands 182 feet wide, 522 feet long, weighs 720 tons and spans 93,678 square feet of space, rising an impressive 66 feet above the train platform. It covers the length of more than one-and-a-half football fields over a tubular steel structure of 11 3-D trusses. Its looks are impressive, but the canopy was designed to withstand Denver’s brutal winters. The roof can carry a snow load of 30 pounds per square foot, and can withstand wind speeds of up to 90 miles per hour.

Installing a tensile fabric structure of this proportion was no easy task. “PTFE coated fiberglass always requires added considerations throughout the project starting with cutting and marking through to installation,” says Bart Dreiling, president of Structurflex American Operations. “In this case, the membrane was panelized onto the structural steel frame. Structurflex’s adjustable extrusion system was used for the PTFE fiberglass throughout most of the project. Monitoring of prestress in the PTFE fiberglass membrane was required by the structural steel engineer of record throughout the course of the installation. A fixed clamping system with rubber ‘bumper’ was used for ETFE clamping at the Amtrak canopies.”

Dreiling says the decision to use PTFE-coated fiberglass fabric was an easy one that was made in the early stages of project planning. “It was agreed upon by the design team, as well as Structurflex, that PTFE fiberglass was the ideal material for the project,” he says. “It offers superior fire resistance, excellent long term structural performance and UV stability.” Dreiling also notes that Structurflex has extensive experience working with PTFE-coated fiberglass fabric and has found it to be the most reliable and well-produced product on the market. It was a natural choice for the iconic Denver Union Station project.

Station installation

Installation of the membranes on each of the structures was handled by Structurflex’s experienced crew. “Our crew consists of tradesmen with experiences ranging from steel erection, carpentry, glazing installation, rope access climbing and general construction,” Dreiling says. “All members of the Structurflex installation team for the project had ample experience installing PTFE fiberglass, PVC-PES and ETFE coming into the project. With the project consisting primarily of PTFE fiberglass, approximately 65,000 square feet, and 15,000 square feet of single layer ETFE, it was important to employ the right crew for the project.”

Even the most experienced of crews will always face unique project-specific challenges.
“Access in some areas was challenging,” Dreiling says, “requiring our installers to walk the steel in many cases. Man lifts were used where equipment access wasn’t restricted.”

The project team faced a large amount of design development and coordination, unique engineering, intricate detailing coordination, fabrication schedules and installation coordination while other traders were simultaneously working in the same space. Constant communication and coordination with all team members was required throughout the project.

Engineers and installers also had to respect special restrictions put in place by the city. Denver has sightline restrictions designed to prevent new construction from blocking mountain views. The installation team used a “kickstand” to support the two seed trusses while putting the roof in place. Forty workers took four months to install the framing, and another six months to complete the canopy installation. A large oval open space was designed into the center of the roof to provide ventilation and open views from the platform.

To keep things running smoothly, Structurflex was ubiquitously present at meetings, conference calls and web conferences for the project. The team also maintained direct lines of communication with the engineer, architect, general contractor, steel fabricator and steel erector.

The Union Station Transit Center opened in May, revitalized as one of downtown’s most thriving attractions. The former abandoned rail yard is now a bustling transit hub, along with new businesses, buildings and transportation options that the area had been lacking for years, all under one roof.

Jake Kulju, a frequent contributor to Fabric Architecture, is a freelance writer from Minneapolis, Minn.

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