Remote Arizona mountaintop observatory gets metal roof
One of the long standing questions in astronomy has been whether planets exist around other stars. Thus far, direct observations of planets have been impossible because of the presence of the very bright stellar image blurred by atmospheric "seeing." Since such a Jupiter-like planet would be roughly a billion times fainter than the star, it would be impossible to detect using traditional techniques.
The Large Binocular Telescope (LBT), equipped with adaptive optics (atmospheric blurring compensation) and fully exploiting the superb quality of its mirror surface will permit formation of images of sufficient sharpness (diffraction-limited) that the planet could be detected against only a low surface brightness halo of residual scattered light.
In this manner, a Jupiter-like planet could be detected, if present, around some 50 of the nearest stars.
The LBT is the largest and most scientifically advanced telescope ever created, located near Safford, Ariz., 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 the world's most respected and accomplished astronomers, physicists, opticians, mathematicians, software developers, and mechanical and electrical engineers.
Specifying the use of advanced, standing seam steel roofing panels demonstrates the critical advantages of metal roofing in challenging situations where strength, light weight and durability are key requirements.
What better material to protect a delicate (and expensive) scientific instrument located high on a remote Arizona mountaintop?
When completed, the LBT will utilize two 8.4-meter (28 feet) mirrors that will enable astronomers to look farther into the universe than ever before - 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-foot elevation and pollution-free atmosphere.
A natural choiceTo meet the design challenges posed by this unique project, the designers, M3 Engineers of Tucson, called for 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., of Houston, and installed by EMCO, the Engineered Metals Company, headquartered in Sacramento, Calif.
"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."
W.J. "Doby" Fleeman of EMCO said his company is involved in a lot of unusual projects, from the Arctic Circle to Antarctica, including another recent telescope observatory roof in Hawaii. "We've always dealt with large engineering firms as an offshoot of our manufacturing operations," he said.
Rising 167 feet 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 23-meter diameter circular rail anchored above ground on a reinforced concrete wall. The LBT will have a collecting area larger than any existing or planned single telescope. It will provide unmatched sensitivity for the study of faint objects.
Each aperture of the binocular telescope has a 10.4-meter wide opening for viewing. These two apertures 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.
The logistics of working up on a mountaintop made this challenging, Fleeman said. "It was a two hour ride from the base to the site, where there was very little layout area. We couldn't have a lot of materials stored up there, so we had to schedule deliveries of materials and supplies precisely as they were needed."
The LBT enclosure rises 167 feet above the ground; the site elevation is 10,470 feet above sea level: a formidable work environment. "Let's just say we didn't send our heavy smokers up there," Fleeman laughs. There was no elevator in operation during construction. To get to the top of the roof meant climbing 170 feet of stairs. "It was tough going more than 4-5 flights of stairs before stopping for a breather," according to Fleeman. Combine that with trying to negotiate those stairs with a 10 foot piece of trim that had to be snaked between the stair rails. "Even one of the younger members of the crew couldn't quite make it up the 18 flights of stairs carrying a 50 lb. box of sealant tape, and required a handoff."
"Weather was also a consideration," said field superintendent Mike Lindloff. "Atop the mountain, it could change in the blink of an eye. One minute you're working in the clouds and next minute it's a heavy snowfall. And some days it just wasn't possible to get up the mountain at all due to surprise snowfalls. Between periods of active lightning and average winds of 10 mph, it was not unusual to see gusting to 50 mph." Needless to say, the importance of proper tie-off and careful attention to securing of materials was of paramount concern at all times.
Another job consideration: as a major breeding ground for the endangered Red Squirrel, each vehicle on the mountain was required to be specially permitted by the University of Arizona.
All panels had to be cut at base camp to prevent dust, and construction debris had to be hauled down on a daily basis. Transit time from Base Camp (El. 3,000 ft) to jobsite (El. 11,000 ft) was "approximately 60 minutes on a good day." A special trailer with a slip access differential was required to maneuver up the winding road.
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:
- 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.
- Efficient operation and service in a remote location, with minimal future maintenance requirements.
- Ability to accommodate a supplemental aluminum tape foil coating to improve emissivity (light reflection) on the finished roofing surface.
- Minimal degradation of the pristine mountaintop environment.
- Cost and budgetary restraints that mandate building efficiency.
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 Ultra-Dek® roofing system is manufactured from .0299 inch steel, which is fabricated into 12-inch 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. Siding consisted of Metlspan factory insulated wall panels.
Building material specifications, developed by the project engineers at M-3 Engineering and Technology, were geared to address two primary construction imperatives: 1) To provide an enclosure with proven, long-term weatherproofing capabilities in a windy, highly exposed and changeable climatic exposure, and 2) To deliver a well insulated enclosure, key to maintaining the stable, interior temperatures necessary to accurate operations of sophisticated telescopic equipment.
EMCO specializes in the supply and installation of construction products and metal roofing systems for the industrial and commercial markets. It was established in 1979 as a manufacturing division of Soulé Steel Company. The company performs its own research on clips and fasteners to determine holding power in high winds. It works in a variety of materials, including bronze and Rheinzink.
Standing seam metal roofing offered additional advantages, including:
- 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.