Main Street Bridge (Hillsboro, Oregon)

The Hillsboro Main Street Bridge is a concrete tied arch bridge located in Hillsboro, Oregon. The bridge carries light rail traffic on the MAX Blue Line over Main Street and 18th Street. Completed in 1997, the 425-foot-long (130 m) bridge was built with a 78-foot-tall (24 m) arch in the center. It is located between the 12th Avenue Station and the Fair Complex Station.

Main Street Bridge
Coordinates45.521416°N 122.963618°W / 45.521416; -122.963618[1]
CarriesMAX Blue Line
CrossesMain Street & 18th Avenue
LocaleHillsboro, Oregon, United States
Maintained byTriMet
Characteristics
Designconcrete arch/tied-arch
Total length425 feet (130 m)
Width34 feet (10.3 m)
Height75 feet (arch)
History
Opened1997

Design
Cables connecting the arch to the rail bed

The bridge is a post-tension box girder structure with the center pier as an arch support straddling the road.[2] Used in lieu of a center support, the arch is 110 feet (34 m) wide[2] and 75 feet (23 m) tall.[3] Six cables measuring four inches (102 mm) in diameter run from the arch to the main structure of the bridge at the center.[3] The two ends of the reinforced concrete arch are connected to each other underground using a post-tension tie beam, making the structure a tied arch.[2]

History

After more than a decade of studies and designing, construction on the Westside MAX light rail line began in 1993.[4] In 1997, construction on the Main Street Bridge began. The bridge was designed by BRW to cross what is planned to be five lanes of traffic on Main Street.[3] The city of Hillsboro required the bridge to be able to cross over the planned widening of the roadway without using a center support column, so as to prevent the kind of accidents that had plagued a previous crossing at the same location,[3][4] a wooden trestle bridge of the Oregon Electric Railway, built in 1917 with a vehicle clearance height of just 10 feet, 6 inches.[5] After abandonment of freight service on the line in the mid-1970s, the city required the successor railroad, the Burlington Northern Railroad, to remove the old crossing, in 1977.[5][6] In September 1997, the construction of the current bridge structure was completed.[7] The "golden spike" of the Westside light rail line was driven with the final pieces of track of the project installed on this bridge in October 1997.[8] Passenger service on the $964 million project began on September 12, 1998.[8]

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References
  1. "Main Street Bridge". Geographic Names Information System. United States Geological Survey. 2010-03-11. Retrieved 2010-03-22.
  2. Cortright, Robert. 2003. Bridging the World. Wilsonville, Or: Bridge Ink.
  3. Arch support for Tri-Met extension; engineers in Hillsboro, Oregon, constructed a 75-foot-high (23 m) concrete arch over a roadway without using a center support, so that the arch can support bridge cables for the light rail overpass; Transit Update. Railway Age, November 1997 No. 11, Vol. 198; Pg. 27; ISSN 0033-8826
  4. Westside light rail the MAX Blue Line extension. TriMet. Retrieved on October 8, 2007.
  5. Boatwright, JoAnn (September 15, 1998). "Bridge new ‘gateway to city’". The Hillsboro Argus, p. 8A.
  6. "East Main Overpass". The Hillsboro Argus. October 19, 1976. p. 18.
  7. Oliver, Gordon and Don Hamilton (August 29, 1997). "MAX moves west: New rail stations will go on-line". The Oregonian, p. A1.
  8. Oliver, Gordon and Don Hamilton (September 9, 1998). "Go west, young MAX". The Oregonian.
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