THE CONCRETE BRIDGE MAGAZINE

SPRING 2017

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/806277

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CONCRETE BRIDGE TECHNOLOGY Salt Creek Half-Viaduct Bridges Rehabilitation Using Full-Depth Precast Concrete Deck Panels by Dr. Keith Kaufman, Knife River Corporation Heavy haul trucks that travel between Portland, Ore., and Weed, Calif., have few route options. Trucks can stay on Interstate 5 (I-5) and deal with multiple passes between Eugene, Ore., and Medford, Ore., before climbing the Siskiyou Summit that is south of Ashland, Ore., and continuing on to Weed. Another popular freight route uses Oregon Route 58, which heads east out of Eugene and over the Cascade mountains to Highway 97 near Chemult, Ore. That route then follows a relatively flatter grade to Weed by avoiding the Siskiyou Summit. Oregon Route 58 is a two-lane highway that leaves the Willamette Valley at an elevation of 500 ft and climbs the Cascade Mountains, reaching a peak elevation of 5100 ft at Willamette Pass. An integral part of this route is the Salt Creek Tunnel, which lies west of the summit at an elevation of 3850 ft. Four half-viaduct bridges are located outside the tunnel: one to the west and three to the east. At each of these locations, the westbound lanes are on grade while the eastbound lanes are supported across multiple grade openings using reinforced concrete deck-girder bridges or half viaducts. The geometry of the tunnel grade was modified by lowering the roadway to improve vertical clearance. Other improvements include applying shotcrete to the walls, and upgrading utilities. The four viaducts also required reconstruction to alleviate years of deterioration and improve the safety of the system. The Oregon Department of Transportation (ODOT) completed a redesign in2012. Design Due to historical requirements, the new bridges had to simulate the T-beam construction of the existing bridges. Therefore, the engineer of record (EOR) detailed a spread 42-in.-deep precast, prestressed concrete box-beam system carrying a 10-in.-thick cast-in-place (CIP) composite concrete deck that would receive a 4-in.-thick asphalt overlay. The thick deck and overlay help resist potential debris slides and avalanche impact. Furthermore, the EOR limited the live load deflection at the longitudinal joint between the eastbound viaduct and the westbound grade so that the asphalt overlay could be continuous over the eastbound and westbound lanes. The individual span lengths are 50 ft on all viaducts with two to five spans in each bridge. The four bridges include longitudinal grades of 4% to 5%. Three of the bridges are on a horizontal curve with a constant cross slope. The EOR’s design included a precast concrete-friendly design for the box beams. All pile caps were parallel, being normal to the chord of the arc. Therefore, all precast concrete box beams were the same casting length. A chamfer or fillet detail was included at the ends to incorporate the proper offset to the curve. The fourth bridge is on a tangent. However, it included a reverse superelevation. ODOT specified its three-tube curb mount rail. The exterior of the curb included a formliner for aesthetics. These details are visible from the Salt Creek Trail below the roadway. Value Engineering and Special Considerations The construction site and schedule were very restricted. The weather limited construction to the late spring, summer, and early fall, depending on snow. Oregon Route 58 was closed during weekday nights to allow for construction. Daily closures were limited to 15 minutes to allow alternating single-lane traffic movements. After the bid, the contractor contacted the manufacturer of the precast concrete box beams, Knife River, and asked whether a full-depth precast concrete deck panel could replace the CIP deck. A post-tensioning supplier, DSI, was contacted and details were provided for a system used in Utah that was pretensioned transversely and posttensioned longitudinally. This system was submitted and approved. For the three bridges on a horizontal curve, pieshaped deck panels were detailed. The panel width was set to match the railpost spacing of 9 ft so that all panels were the same in each bridge.

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