Seattle — Multidisciplinary engineering and consulting firm Arup served as technical advisor for a 400-foot-tall, free-standing flagpole owned by ACUITY Insurance Company in Sheboygan, Wis. The pole, which is currently the largest in the United States, was dedicated in June amid comments from Wisconsin Governor Scott Walker, and appearances by skydivers and military dignitaries. Twenty-five ACUITY employees, who are military veterans, carried the 350-pound, 60-foot by 120-foot American flag that was lifted onto the pole during the ceremony.
“ACUITY erected its first flagpole after 9/11 as a tribute to our nation’s soldiers, and from there its meaning, intent and symbolism have grown to mean many different things to many different people. During this latest installation we knew this was much bigger than a construction project and we were committed to doing it right in order to provide our community with a beacon of hope and patriotism well into the future,” said Sheri Murphy, ACUITY’s vice president, services & administration and flagpole project lead. “It brought a great sense of comfort and confidence to our team knowing we had Arup’s experience and expertise guiding all aspects of the project on our behalf. They helped us stay focused and the end result is exactly what we were striving for. It was wonderful to have them by our side.”
ACUITY appointed Arup to review and oversee all technical aspects of the flagpole’s design and fabrication, which included wind engineering; supplemental damping design; cold weather engineering; metal fatigue analysis; geotechnical, electrical, and mechanical engineering; moveable structures; corrosion protection; lighting; and security camera review. Key engineered components of the flagpole include a rotating truck slew bearing assembly at its top, and three pendulum-type tuned mass dampers within the pole to suppress the first three modes of cross-wind oscillations.
“It’s easy to underestimate the engineering challenges,” said structural engineer Hans-Erik Blomgren, who served as Arup’s lead designer. “There’s some really specialty engineering involved. In particular, the need to withstand oscillating in the wind, subzero temperatures, and ice that the flagpole will frequently be exposed to during its 50-year lifespan required careful consideration.”
ACUITY enlisted Arup as technical advisor for the project upon hearing about its engineering design for the 394-foot-tall Spire of Dublin. Arup relied upon engineering experts from throughout the firm to scrutinize the design to ensure the flagpole can be sustained for a 50-year design life.
“Current design standards and codes of practice do not adequately cover projects of this nature,” said Cormac Deavy, Arup’s principal in charge for both the ACUITY and Spire of Dublin projects. “These projects require fundamental research into the physics of the problem and rely upon ‘first principles’ engineering and a fundamental understanding of the loads, materials, and structural response to create elegant, efficient designs.”
A site-specific wind and climate report determined that the flagpole should be designed for a low service temperature of minus 41 degrees Celsius. Dampers will suppress vibrations and help to reduce fatigue on the flagpole.
In addition to the Spire of Dublin, Arup has also completed similar projects, such as the United States Air Force Memorial and the flagpole at King Abdulla Square in Jeddah, Saudi Arabia, which currently stands as the world’s largest flagpole.
Key collaborators on this project included contractor Mortenson; US Flag & Flagpole Supply; structural engineers APE Inc., and tuned mass damper supplier Flow Engineering.
View a time-lapse video of construction at http://acuity.phanfare.com/flag/6522234#imageID=215175191.