Three Sisters Bridges

Pittsburgh, Pennsylvania

The Three Sisters Bridges are perhaps the most iconic in Pittsburgh, spanning the Allegheny River and connecting the downtown business district to North Shore. The crossings were built between 1924 and 1928 and required rehabilitation because of accelerating age-related deterioration. Partnering with owner Allegheny County, Michael Baker provided preliminary engineering, final design and construction-phase services.

The Three Sisters Bridges are the only trio of identical, side-by-side bridges in the world, yet they have aged in different ways. The Michael Baker team approached each rehabilitation separately, combining recognition of historical significance with modern engineering practices to complete a structurally superior, sustainable rehabilitation project that was also sensitive to the historic nature of the bridges and eye-catching. The existing hold-down mechanisms were replaced in their entirety using temporary systems to maintain the existing bridge vertical geometry. Structural steel repairs were provided as required to increase member strengths as well as repair damage from corrosion and vessel strikes on the Allegheny River.

The Andy Warhol Bridge rehabilitation (2016-2018) involved the replacement of the concrete bridge deck; full repainting of the superstructure; steel repairs of the fascia beams and sidewalk framing, floor beam connections, stiffening girders and sidewalk brackets, substructure repairs, and installation of scour protection.

Work on the Rachel Carson (Ninth Street) Bridge (2019-2020) included repairs to steel members and replacement of the concrete deck. Service lines for utilities were replaced and the expansion dams and drainage systems were replaced. The updates included new sidewalk framing and sidewalks.

The Roberto Clemente (Sixth Street) Bridge rehabilitation (2022-2023) required the replacement of the existing deteriorated concrete deck, structural steel repairs (including a complete eyebar hanger replacement), replacement of the sidewalk framing and concrete sidewalks, and replacement of the bridge hold-down mechanisms.

Also, the rehabilitated bridges are each painted Aztec Gold and feature more than 600,000 LED lights that can be synchronized for light shows.

With the rehabilitation complete, Pittsburgh locals and visitors can enjoy a convenient, safe and beautiful river crossing for decades to come.