How do you protect a scientific instrument of amazing complexity and precision when it is located on a remote Arizona mountaintop? That was the challenge facing a consortium of universities and scientific organizations as they launched a project to build the most powerful ground-based telescope in the world on Mount Graham, near Safford, AZ.
Their solution is an advanced-standing seam-steel roofing panel strong enough to sustain high winds and ultraviolet radiation, yet light enough to be transportable to the remote site. The design and installation of this roofing system demonstrates the critical advantages of steel roofing in challenging situations where strength, light weight and durability are key requirements.
Project Overview
The Large Binocular Telescope (LBT), one of the largest and most scientifically advanced telescopes ever created, is being constructed on a remote mountaintop near Safford, AZ, as part of the Mount Graham International Observatory. With a construction budget of approximately $80 million, the LBT project is the result of the combined efforts of respected and accomplished astronomers, physicists, opticians, mathematicians, software developers, and mechanical and electrical engineers.
When it is completed, the LBT will utilize two 28-ft. (8.4 m) mirrors that will enable astronomers to look farther into the universe than ever before — possibly exceeding the performance of even satellite-mounted telescopes such as the Hubbell Space Telescope. The building that encloses these instruments would pose significant design and construction challenges in any location, requiring a rotating enclosure with a complex system of movable shutters that open skyward. In the case of the LBT, however, these demands were further complicated by the remote southern Arizona location, found to be ideal for many space observation instruments that require the area’s 10,500-ft. (3,200 m) elevation and pollution-free atmosphere.
To meet the design challenges posed by this unique project, the designers, M3 Engineers of Tucson, AZ, specified a steel structure for the LBT enclosure, which was erected by Schuff Steel of Phoenix. The factory-insulated metal roofing was manufactured by MBCI, a subsidiary of NCI Building Systems Inc., Houston, TX, and installed by EMCO, the Engineered Metals Company, headquartered in Sacramento, CA.
“Steel roofing was the natural selection for this project, based on its light weight and high strength-to-weight ratio,” said Michael Werner of the American Iron and Steel Institute. “The Ultra-Dek roofing panels offered unique characteristics that accommodate large spans between trusses, as well as resistance to extremely high wind pressures and snow loads at this remote location.”
Roofing Design
Requirements
Rising 167 ft. (50.9 m) above the ground, the basic design of the LBT building is a rotating box, that surrounds the telescope itself. Resting on a circular pier, the rotating building rides on a 75-ft. (23 m) diameter circular rail anchored above ground on a reinforced concrete wall.
Each opening of the binocular telescope has a 34.1-ft. (10.4 m) wide opening for viewing. These two openings are covered by sliding shutters which move apart laterally to open the slits. Additional openings on the back and sides enable natural wind ventilation to flush the building. When the wind is strong, a windscreen can be raised to protect the telescope from buffeting.
This unique design posed a number of design and construction challenges for the building’s roofing system. Among the requirements the roofing system had to address were the following:
• Design flexibility and high strength-to-weight ratio to allow the long open spans required by the truss design.
• Unfailing protection of the sophisticated telescope from the elements, including potential wind speeds of up to 120 mph (193 kph).
• Efficient operation and service in a remote location, with minimal future maintenance requirements.
• Ability to accommodate a supplemental aluminum tape foil coating to improve light reflection on the finished roofing surface.
• Minimal degradation of the pristine mountaintop environment.
• Cost and budgetary restraints that mandate building efficiency.
Solutions and
Advantages
The unique demands of the LBT enclosure building were met with a standing seam steel roofing system, manufactured by MBCI and installed by EMCO. The UltraDek roofing system is manufactured from .0299-in. (.075 cm) steel, which is fabricated into 12-in. (30.5 cm) wide trapezoidal shaped panels and finished with a Galvalume finish for maximum resistance to the elements. The narrow panels were specifically selected to meet the load bearing and structural spanning requirements of the LBT enclosure, and installed on a very low-slope (1/2:12) configuration.
Standing seam metal roofing also offered additional advantages, including the following features:
• Superior resistance to wind uplift.
• Exceptional strength and design flexibility to accommodate the movable shutter door design.
• Light weight and relative ease of transportation to the remote location.
• Minimal on-site waste, resulting in lower transportation and disposal costs.
• Long life with minimal maintenance, requiring fewer trips to the remote site for routine maintenance or repairs.
• An ideal substrate for applying the supplemental aluminum tape foil coating.
• Manufactured from recycled, environmentally friendly material that can be recycled again if desired in the future.
Conclusions
The combined challenges of a highly complex structure and extremely remote site made standing seam metal roofing an ideal selection for the Mount Graham LBT enclosure.
In addition, the remote location and extreme climate conditions further highlight the advantages of standing seam steel roofing, offering weather resistance and flexible, low-slope design options.
For more information, call 888/544-6447, or visit www.steel.org.
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