As part of the community and economic revitalization effort around Chicago’s Old Post Office, Canal Street Plaza’s reconstruction required an innovative construction approach thanks to its structure-on-structure design.

Crews also navigated a complex work area. At track level are Amtrak commuter lines. Above is a viaduct structure—owned and maintained by the Chicago Dept. of Transportation—that is attached to the privately owned 100-year-old post office. Cutting through that building and bearing on the viaduct structure is also an Illinois Dept. of Transportation expressway.

Since the new superstructure is tied into the existing steel structure, the contractor carefully planned steel fabrication, including detailed surveys, field measurement verifications and 3D modeling to locate and integrate utilities.

Limited as-built documents existed for the structure. As demolition progressed, crews uncovered varying connection types, deterioration and unknown conditions. The team developed several design options that could be applied based on actual conditions, using new data to make modifications as work progressed. The project team often redesigned the superstructure on the fly, but crews successfully made all tie-ins with the original structure without service interruptions or schedule delays.

Documenting work, from the initial surveys and 3D scans to drone footage resulted in a revitalized superstructure.