page_title: Three Sisters (Pittsburgh)
hierarchical_section_title: Three Sisters (Pittsburgh)
caption_attribution_description: English: Jet Lowe, photographer, summer 1999. PA-490-A-16 (CT) SUSPENDER DETAIL, LOOKING NE WITH OTHER TWO SISTERS IN BACKGROUND.
context_page_description: The Three Sisters are three very similar self-anchored suspension bridges spanning the Allegheny River in downtown Pittsburgh, Pennsylvania at 6th, 7th, and 9th streets, generally running north/south. The bridges have been given formal names to honor important Pittsburgh residents:
  Roberto Clemente
  Andy Warhol
  Rachel Carson
  Designed by the Allegheny County Department of Public Works, they were all built in a four-year period, from 1924 to 1928, by the American Bridge Company, replacing earlier bridges of various designs at the same sites. Their construction was mandated by the War Department, citing navigable river clearance concerns. They are constructed of steel, and use steel eyebars in lieu of cables.
  The Three Sisters are historically significant because they are the only trio of nearly identical bridges, as well as the first self-anchored suspension spans, built in the United States. They are among the only surviving examples of large eyebar chain suspension bridges in America, and furthermore, unusual for their self-anchoring designs. The bridges’ design was viewed as a creative response to the political, commercial, and aesthetic concerns of Pittsburgh in the 1920s.
context_section_description: The Three Sisters are three very similar self-anchored suspension bridges spanning the Allegheny River in downtown Pittsburgh, Pennsylvania at 6th, 7th, and 9th streets, generally running north/south.  The bridges have been given formal names to honor important Pittsburgh residents:
  Roberto Clemente (Sixth Street Bridge)
  Andy Warhol (Seventh Street Bridge)
  Rachel Carson (Ninth Street Bridge)
  Designed by the Allegheny County Department of Public Works, they were all built in a four-year period, from  1924 to 1928, by the American Bridge Company, replacing earlier bridges of various designs at the same sites. Their construction was mandated by the War Department, citing navigable river clearance concerns. They are constructed of steel, and use steel eyebars in lieu of cables.
  The Three Sisters are historically significant because they are the only trio of nearly identical bridges, as well as the first self-anchored suspension spans, built in the United States. They are among the only surviving examples of large eyebar chain suspension bridges in America, and furthermore, unusual for their self-anchoring designs. The bridges’ design was viewed as a creative response to the political, commercial, and aesthetic concerns of Pittsburgh in the 1920s.
  The bridges were designed under the auspices of the Allegheny County Department of Public Works, by T. J. Wilkerson, consulting engineer; Vernon R. Covell, chief engineer; A. D. Nutter, design engineer; and Stanley L. Roush, architect.  The American Bridge Company built the superstructure; while the Foundation Company built the substructure.
  All three bridges are owned by Allegheny County.
caption: View of Sixth, Seventh and Ninth Street Bridges from downriver
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