When the Mackinac Bridge, the world’s fifth longest suspension structure, needed sprucing up after more than 60 years connecting Michigan’s peninsulas, new and innovative engineering approaches were required to strip its two towers to bare metal for a fresh coat of paint.

An elaborate, first-of-its-kind movable platform system designed by Ruby+Associates Structural Engineers, fabricated by Moran Iron Works and used (and patented) by Seaway Painting, allowed that massive job to be done efficiently, while also earning several structural engineering awards (see list below). This includes the Society of Protective Coatings’ E. Crone Knoy Award for outstanding achievement in industrial or commercial coatings. The award was named for the deceased 1958 mechanical engineering alumnus.

Andrew (Drew) Twarek, a 2005 civil engineering graduate, was the engineering team project manager for Ruby+Associates tasked with using state-of-the-art techniques and creative new products to solve problems that provide long-term service.

“It’s not often that an engineer gets to work on such an iconic structure,” states Twarek about the bridge, with a suspended length that stretches 8,614 feet between anchorages and has a total length of approximately five miles. “Most projects are on firm ground, with straightforward loading. This project was 500 feet in the air above water, so the wind load was significantly higher (considering winds regularly exceeding 100 mph at the top of the towers). The combination of aluminum and steel with the hoists involved added another layer of complication to the design.”

The Ruby team designed two different  hanging platforms to allow for removal and collection of the original lead-based paint, and to repaint the towers. A davit-like “outrigger” system mounted to the top of the tower supported the platforms, which were raised and lowered using traveling hoists and cables to allow painting the upper 320 feet of the towers, high above the bridge deck used by an estimated 11,600 motorists daily.

The tower leg platform was designed to be preassembled and erected into place in two sections. Once assembled, the tower leg platform encircled three sides of the tower leg, with removable planks across the fourth side to allow it to travel past the tower struts. The upper work surface was made of grating to allow sand and paint particles to fall to the bottom platform for vacuum extraction. Steel was used for strength at the floor level, with an aluminum superstructure to reduce weight and allow painting on multiple levels at once.  Canvas walls ensured that debris was contained and both blasting and painting work was able to be performed in high-wind conditions. 

Making the entire process possible, Ruby engineers also provided erection engineering, construction engineering, heavy lift, and fabrication detailing services to complete the project.

Then, the entire system was reused to complete the bridge’s south tower in 2020.

Twarek states about the once-in-a-lifetime project, “It took a lot of innovation to develop the right system. The project wasn’t a ‘cookie cutter’ project, where we are asked to run some numbers and develop fairly simple solutions. We had a general concept, but then had to figure out how to overcome the hurdles and make it work efficiently. We’re very proud of what our team accomplished. When it received statewide and national attention, that was just the icing on the cake!”

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Prize Project

The Mackinac Bridge Paint Platforms project has earned the following awards:

• 2020 Other Structures Outstanding Project Award - National Council of Structural Engineers Association
• 2020 Honorable Conceptor Award - American Council of Engineering Companies/Michigan
• 2020 E. Crone Knoy Award - Society for Protective Coatings - (Seaway Painting)
• 2019 Excellence in Structural Engineering, Best Neighboring State Project Award - Structural Engineers Association of Illinois