Also known as the Roberto Clemente (Sixth Street), the Andy Warhol (Seventh Street), and the Rachel Carson (Ninth Street) Bridges, the Three Sisters reflect historic bridge design and construction feats, and make up the only trio of identical, side-by-side bridges in the world and are the first self-anchored suspension bridges constructed in the United States. Michael Baker was selected for preliminary engineering, final design and construction-phase services for the rehabilitation of each of the 90-year old historic bridges – owned and maintained by Allegheny County.
The bridges require rehabilitation because of accelerating age-related deterioration. The project work draws on our expertise in all areas of bridge design, construction, and preservation and includes the following: bridge inspections; structural analysis and rehabilitation design; utility coordination; maintenance and protection of traffic; roadway and lighting design; paint evaluation; field surveys and public involvement.
As part of the structural analysis, our team developed a series of three-dimensional, finite-element models for the Andy Warhol Bridge using MIDAS, an engineering software specifically developed for bridge modeling and analysis. The models were used to establish the existing forces on the bridge, determine the new dead loads based on the proposed rehabilitation, calculate the modern-design live loads and evaluate proposed construction sequencing.
Currently, the first of the three bridges, the Andy Warhol Bridge, is fully open to vehicular and pedestrian traffic. Construction work involved the following: replacement of the bridge deck and joints; total repainting of the superstructure; steel repairs; replacement of the main span tie-down assemblies; replacement of the existing lighting with historic replica light poles; substructure repairs; scour protection; replacement of utility conduits and bracing; and replacement of downspouts and scuppers.
Rehabilitation of the Rachel Carson Bridge began in the summer of 2018, construction is scheduled to begin in the spring of 2019 and be completed by the summer of 2020. The Roberto Clemente Bridge rehabilitation will start in the summer of 2020 and end by the fall of 2021.
“We look forward to continuing our bridge rehabilitation work with our partners at Allegheny County, utilizing our experience and commitment to excellence in bridge design, to significantly extend the life of these iconic structures.”
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