(CS1.1) Structural Considerations when Replacing Antiquated Building Materials: Restoring Michigan Central Station's Skyline

The Michigan Central Station is an iconic landmark in the heart of Detroit’s Corktown neighborhood and was once a bustling center of commerce, transportation, and community. The 640,000-square-foot Beaux Arts train station and 18-story office tower were designed by the two architecture firms Warren & Wetmore and Reed & Stem in 1911. At the time, it was the tallest train station in the world. It served as the main passenger depot for the city and continued to function as a passenger rail station until 1988, when it was abandoned and left vacant for three decades. When Ford purchased the site in 2018, they brought together a team of historic building specialists who have been working the past 6 years on restoring the landmark.

The 18-story office tower stands 230 feet tall and is comprised mostly of brick exterior cladding with cast iron window spandrels, but the topmost floors are detailed with ornate terra cotta elements, including perimeter Juliet balconies and a 10’-0 long projecting cornice. For each of these elements, Silman was charged with investigating and understanding how these ornate and heavy cladding elements were supported and in what condition the supporting structure was. Original documentation was studied to develop an initial, localized exploratory review of the rooftop cornice and 12th office floor Juliet balconies. The results of this first site work program yielded interesting results, which informed how the rest of the assessment and repair strategies were to be completed.

The results of the localized probes found that the full removal of the topside cornice slab and 10th floor decorative banding and balconies would be needed to assess and repair the hundreds of miscellaneous pieces of steel that secured the terra cotta elements. Silman spent countless hours developing “live” construction documents for the tagging, assessment, and recommendation for the necessary steel elements, including major steel spandrels, shelf angles, cantilevered angles, J-bolts, etc. These documents were updated daily and handed to the contractor within 24 hours so that repairs can begin that same week, allowing the contractor to work their way around the perimeter of the building.

As for the cladding material elements themselves, many areas, particularly the Juliet balconies, showed that the terra cotta elements and their anchorage were not salvageable. Replacing in kind with terra cotta was not viable from a constructability or cost perspective. After many workshops with the client, the team decided most of the terra cotta would be replaced with GFRP (glass fiber reinforced polymer). While significantly lighter than its predecessor, GFRP would have specific challenges that the design team needed to resolve to ensure the marriage of historic elements and the contemporary materials would be seamless.