The Wisconsin Department of Natural Resources (WDNR) retained Ayres to develop conceptual planning alternatives and then final designs for the new Eagle Tower at Peninsula State Park. The tower is a prime attraction at the Door County park, which attracts an estimated 1 million visitors annually.
The Wisconsin Section of the American Society of Civil Engineers awarded the project the 2022 Engineering Achievement Award for projects with a construction cost between $2 million and $10 million.
Ayres worked collaboratively with WDNR staff, local stakeholders, and the U.S. Forest Products Laboratory to develop design options for a new tower on the footprint of the previous Eagle Tower, which was closed in 2016 after structural damage was found.
Our team developed a series of options ranging from helical ramps to elevator systems to a combination ramp/staircase solution. Challenges included a lack of electrical service within 1.5 miles, shallow bedrock, the desire for lofty views of Green Bay and Door County, and accessibility requirements under the Americans with Disabilities Act. Those requirements have stood in the way of replacing similar towers around the nation as they have deteriorated.
After using an unmanned aerial system (drone) to document the view from 35, 45, 55, and 65 feet above the tower site, the team determined a tower height of 55 feet would afford visitors the types of views they got from the former tower, which stood 75 feet high. The 55-foot height also allowed an impressive but practical ramp to be designed to get disabled visitors to the top, saving a considerable dollar amount compared with an elevator system. The tower can be navigated by the winding, 850-foot-long ramp or by the 95 stairs at the core of the tower. The ramp was designed to not only minimize impacts to the forest, but also to make the tower a destination and a learning opportunity in and of itself as visitors rise through the forest canopy toward the observation tower.
Once the ramp concept was approved, Ayres provided final designs, including working drawings and specifications. Special attention was paid to user comfort by minimizing movement of the tower through cross bracing and appropriately sized glue-laminated (glulam) timbers. Tower supports were pinned into the bedrock and positioned to avoid impacts to a pavilion that has long stood near the tower site. The ramp and tower were designed to not only handle large crowds, but also emergency and maintenance vehicles.
Site design efforts improved pedestrian movements, parking, and links to adjacent trails. Plan options and final plan graphics were produced using 3D modeling software. Our team also assisted with the bidding phase and provided construction observation. The $3.7 million wooden tower and ramp were completed in the spring of 2021.