Door County’s Eagle Tower is Back and Better than Ever
Written By: Dan Sydow, PE, Ayres
Door County, Wisconsin, is known for having unique and stunning landscapes. Eagle Tower, situated on Eagle Bluff in Peninsula State Park, was a location that thousands of tourists flocked to each year to get an eagle’s view of these landscapes. Standing above the trees at a height of 76 feet allowed visitors to truly get a bird’s-eye view of the peninsula. Unfortunately, Mother Nature took a toll on the structure, and after serving the public for over 80 years, the ailing tower became structurally insufficient and closed in 2015. It was then dismantled in 2016.
The love for Eagle Tower can be felt in the commitment undertaken to bring it back to life.
Ayres was first hired early in 2017 to aid in the design process and to help determine what was possible. Extensive research revealed that nothing currently in existence was a good fit. The Americans with Disabilities Act (ADA) required that minimum accessibility standards must be followed on all new publicly built structures. With the new standards in mind, Ayres worked collaboratively with Wisconsin Department of Natural Resources 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.
The new tower had to be built under a tight budget, which meant no costly elevators. But it still had to comply with the ADA, so a completely new design was needed, and it had to make minimal impact on the natural forested surroundings. In short, this was a nearly impossible feat, which explains why many similar structures across the country have been coming down and are not being replaced.
By using an unmanned aerial system (drone) to document the view from 35, 45, 55, and 65 feet above the tower site, the team was able to determine 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 practical ramp to be designed, allowing people of all abilities the chance to get to the top and see these views for the first time. Previously, with only one way up the 100-plus stair climb, only the fittest of individuals could make it up to enjoy the view. Today, people of all abilities can now make their way up via a specially designed 850-foot, fully accessible ramp through the surrounding tree canopy. For those craving a challenge, the tower still offers a 95-stair climb.
Guiding the planning for the new Eagle Tower was stakeholders’ commitment to nature-based design. The team didn’t want to build something out of steel or concrete that didn’t fit the natural environment of that area, which meant exploring alternatives that were not only from sustainable resources, like timber, but also would be appropriately treated to last for the long haul. The Ayres structural engineering team worked in consultation with the world-renowned federal Forest Products Laboratory, a part of the U.S. Forest Service, to select materials for the new tower. The design team met with the timber experts from the Madison-based research facility to discuss desirable types of materials to use and how to incorporate the latest research results into best practices to ensure the tower not only matched the natural environment but also performed well long into the future.
The primary construction materials selected were deck boards of solid sawed cedar; glulam beams and columns fabricated from Southern Pine and an adhesive rated for outdoor exposure; steel plate connectors fastened with various bolts, nails, and screws to connect the glulam beams and columns; steel tie rods (large X-shaped rods on the sides of each tower used to resist wind loads); and reinforced concrete foundations that are anchored to shallow bedrock with rock anchors.
The ramp was specially designed to minimize forest and weather impacts, 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. The Eagle Tower project not only allows a wider range of visitors the opportunity to see the majestic views, it also improved pedestrian movements, parking, and links to adjacent trails at the site.
Eagle Tower III is currently the only known wooden structure of this type that is fully ADA accessible in the Midwest. It is hoped that it will not be the only one for long, and that the technology used on this structure could be replicated to rebuild other similar aging towers around the country.
The Eagle Tower project was completed in the spring of 2021. It is estimated that over 1 million people visit the site annually.
About the Guest Blogger
Dan Sydow, PE, is manager of structural engineering in Ayres’ Eau Claire office. Dan leads the group in the pursuit of successful projects, performing project management and engineering for highway and pedestrian bridges, buildings, dams, retaining walls, tunnels, existing structure assessments and renovations, and structural repairs. Dan was the project manager for the Eagle Tower project.
Ayres, a longtime member of ACEC, is a team of 350+ innovative problem-solvers nationwide, standing with integrity behind thousands of projects that strengthen communities and our country’s infrastructure, economy, and environment. Ayres is based in Eau Claire; it has four additional offices in Wisconsin, as well as offices in California, Colorado, Florida, Minnesota, and Wyoming.