ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/319569
C O U N T Y m innesota has 14,368 bridges on the local highway system. Approximately 13% are classified as structurally deficient or functionally obsolete with an age of 60 years or older. Over the past decade, Minnesota has been replacing its aging local bridge system at a rate of approximately 215 bridge structures annually. The structure types commonly used for replacement in Minnesota are 25% precast concrete culverts, 33% cast-in-place concrete slab spans, 35% precast, prestressed concrete I-beams, 3% steel beams, 2% timber, and 2% precast concrete arch bridges. Recognizing an opportunity to possibly expand the local bridge inventory with long lasting, economical, and rapidly built bridges, a Minnesota Local Bridge Scanning Tour (LBST) team was formed. The LBST team was initiated in 2006 by the Minnesota Department of Transportation (Mn/ DOT) office of State Aid for Local Transportation and the Minnesota Division Office of the Federal Highway Administration (FHWA). The primary purpose of the LBST team was to visit other states across the nation that owned or contained local bridge types proven to be safe, durable, economical, and that can be rapidly constructed. The team consisted of several local bridge consultants, county engineers, and FHWA and state DOT representatives. Early in the development of this initiative, it was realized that consultation with industry experts would help the team locate specific areas of the nation to assure a successful scanning tour. The team met with the Precast/ Prestressed Concrete Institute, U.S. Forest Service, and conversed with the National Steel Bridge Alliance. After extensive consideration and input from our nation's experts, the team selected the states of New York and Washington to begin the bridge tours. These states were selected primarily due to their extensive use of precast concrete bridge systems, similar weather and environment to Minnesota, and a good representation of urban and rural roadways. The tour of New York in October 2006 emphasized the west region of the state and included Erie, Cattaraugus, Allegany, and Steuben counties. The team became very interested in their adjacent precast, prestressed concrete box beam system for local bridges. In Washington State in 2007, the team's focus area was the east and northwestern regions of the state including Spokane, Adams, Whatcom, and Tacoma counties. The team was impressed with their advanced and predominate use of precast, prestressed concrete technology. Notable local bridge types that stimulated the team's interest were the adjacent precast, prestressed concrete bulb-tee beam bridges, and the precast, prestressed concrete spliced bulb-tee girder bridges. The team also scanned timber and steel bridges during these tours. At the conclusion of the New York and Washington visits, the LBST team decided to pursue and implement the adjacent precast, prestressed concrete box beam system as a new Minnesota local bridge type. In 2008, Blue Earth County, Minn., and the county's local bridge consultant, with support from the FHWA and Mn/DOT, began developing a local bridge project to demonstrate the New York-style adjacent box beam superstructure, metal traffic railing, and steel sheet pile abutments. The bridge superstructure called for adjacent 2-ft 3-in.-deep by 4-ft 0-in.-wide precast, prestressed concrete box beams to achieve a 32-ft 0-in.-wide roadway with a span of approximately 70 ft. The bridge superstructure also incorporated a 6-in.-thick composite cast- in-place concrete slab overlay. To keep up the momentum and the success of the scanning tours, in 2009, several members of the LBST team took a day trip to Monroe County, Wis., where they visited several bridges that used adjacent precast, prestressed concrete box beams with noncomposite, cast-in-place concrete slabs and bituminous overlays, and side-mounted metal traffic railings. Once again, the MINNESOTA Local Bridge scanning tour by Dave Conkel, Minnesota Department of Transportation An adjacent precast, prestressed concrete box beam bridge with top-mounted metal traffic railing located in Erie County, N.Y. The erection of an adjacent precast, prestressed concrete box beam bridge on steel sheet pile abutments. This is a demonstration bridge in Blue Earth County, Minn. ASP10-1704.indb 50 9/17/10 2:06 PM