THE CONCRETE BRIDGE MAGAZINE

FALL 2015

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/575053

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PROJECT Interstate 5 Whilamut Crossing Bridges over the Willamette River Design by Eric E. Bonn, OBEC Consulting Engineersity. It can be easy to overlook the 84-ft-long north approach spans in these nearly 2000-ft-long bridges, especially when the main spans are the award-winning arches of the Interstate 5 (I-5) Whilamut Crossing Bridges over the Willamette River in Eugene, Ore. However, these apparently straight-forward, utilitarian structures incorporated several unique engineering aspects. The design and construction of the main spans are detailed in an article in the Summer 2012 issue of ASPIRE. Bridge Type Selection Span 1 of Whilamut Crossing Bridges land on the north bank of the Willamette River within the limits of the city of Eugene's Alton Baker Park. The approach roadway is on earth fill. The span's two arches are founded near the riverbank and have one of the major park trails running under them. Span 1 is the transition between the approach fill and the arch spans. Various alternatives were considered for this transition, including retaining walls and precast concrete box or bulb-tee girders. Typical mechanically stabilized earth (MSE) walls could have eliminated the need for the span 1 structure. However, the mass of the 40-ft plus tall MSE wall that would be required was not in keeping with the light and airy appearance of the arch spans and would visually close in the recreational path corridor. Standard Oregon Department of Transportation (ODOT) precast, prestressed concrete box girders or bulb-tee girders could support the span, but the transition between the precast concrete approach span and cast-in-place concrete main spans was determined to be visually unappealing and not in keeping with the clean, repetitive pattern desired. To best combine span 1 with the rest of the structure, it was designed to mimic the adjacent main spans. In the arch spans, the main elements supporting the deck structure are longitudinal T-beams that are supported by spandrel columns springing from the arch ribs. The 10-in.-thick deck spans about 11.75 ft longitudinally between transverse floor beams that frame into the T-beams. The 6.75-ft-wide deck overhangs are supported directly from the T-beams. The floor beams are 40-ft-long, 10-in.-wide, and 2-ft 9-in.- deep precast, prestressed concrete rectangular sections. The same floor PROFILE INTERSTATE 5 WHILAMUT CROSSING BRIDGES OVER THE WILLAMETTE RIVER/EUGENE, OREGON OREGON DEPARTMENT OF TRANSPORTATION, OWNER BRIDGE DESCRIPTION: Each north approach span consists of two simple span, cast-in-place, post-tensioned T-beams with a span of 82 ft. STRUCTURAL COMPONENTS: Each structures consists of two 7-ft-wide, 5-ft-deep T-beams with precast concrete transverse floor beams spanning between them. BRIDGE DESIGN ENGINEER: OBEC Consulting Engineers, Eugene, Ore. PRIME CONTRACTOR: Hamilton Construction, Springfield, Ore. POST-TENSIONING SUPPLIER: Schwager-Davis Inc. San Jose, Calif. PRECASTER: Knife River Prestress, Harrisburg, Ore.- a PCI-certified producer.

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