2024 MidAtlantic Best Projects
Award of Merit, Renovation/Restoration: Three Sisters Bridge Rehabilitation
Photo courtesy Michael Baker International
Three Sisters Bridge Rehabilitation
Pittsburgh
Award of Merit
Submitted by: Michael Baker International
Owner: Allegheny County Dept. of Public Works
Lead Design Firm: Michael Baker International
General Contractor: Mosites Construction Co.
While essentially identical, Pittsburgh’s most iconic bridges built in the 1920s aged differently. The team approached each rehabilitation separately, combining recognition of historical significance with modern engineering practices.
While all three bridge rehabilitations involved replacing the concrete bridge decks, the Andy Warhol Bridge’s superstructure was repainted. The team repaired steel members on the Rachel Carson Bridge. The Roberto Clemente Bridge rehabilitation involved structural steel repairs.
The existing hold-down mechanisms were replaced in their entirety, using temporary systems to maintain the existing bridges’ vertical geometry.
Due to the bridges’ age, history, and importance to the city, materials not normally used in modern bridge construction were required to complete the rehabilitations, including unique tie-down anchorages combining high-strength, post-tensioning bar and high-early-strength cement grouts.
The $35.7-million project was completed at budget in approximately seven years.
Thousands of rivets were replaced with high-strength bolts with button heads to mimic the look of historic rivets. Bolts were installed with an electric wrench that allowed them to be inserted and tightened from one side, thereby providing uniform torque on the nuts and uniform pretension in the bolts. Fracture-critical tie-downs were replaced with new tie-downs to add redundancy.
