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/697527
State Route 162 is a two-lane highway that services several rural towns in western Washington. This short section of highway, only 17.5 miles in length, contains 10 separate water crossings. One of these crossings is over the Puyallup River near the town of Orting. A uniquely designed concrete truss bridge had been in service over the river for some 81 years. This historical, existing bridge had reached its functional limitation, which required that a replacement structure be built: the State Route 162/6 Puyallup River Bridge. The New Bridge A new roadway alignment was designed t o al lo w t he re pl ac em e nt b ri d ge to be constructed adjacent to the existing bridge. This made it possible to maintain traffic during construction. The new alignment required a 3300- ft radius horizontal curve throughout most of the length of the bridge. The replacement bridge contains two spans of prestressed, lightweight concrete girders with a 7.5-in.-thick, cast-in-place, reinforced normal-weight concrete bridge deck supporting concrete traffic barriers at each side. The two spans are 110 and 160 ft for an overall length of 270 ft. A nonsymmetrical span arrangement was chosen to allow the center pier to be constructed out of the river, on the bank, while maintaining an opening large enough to meet the hydraulic requirements of the river. The 40-ft curb-to-curb width allows for two, 11-ft-wide lanes and two 9-ft-wide shoulders. Girder Selection The initial girder choice was to utilize the Washington State Department of Transportation (WSDOT) WF74G girder type, which is a 74-in.-deep girder with a 49-in.-wide top flange. The WSDOT bridge and structures office was looking for a suitable structure to evaluate the use of prestressed, lightweight concrete girders and selected this bridge due to its limited size and medium- length spans. The use of prestressed, lightweight concrete girders had been contemplated in the past, but concerns about girder properties—specifically the modulus of elasticity, creep, and shrinkage values—deterred WSDOT from using them. Advantages Weight reductions as a result of using lightweight concrete for the production of girders generally helps reduce substructure sizes. For instance, the depth to which shafts require embedment is controlled by either vertical or lateral loads. The vertical loads are reduced in two ways. The most obvious way is from the reduced girder weights. However, reduced girder weights can also reduce the size of pier crossbeams, which further reduces the dead load. These combined reductions lead to a smaller mass in the superstructure, which can reduce the seismic lateral loads to the foundations. These smaller foundation elements lead to cost savings in construction of the bridge. Reduced girder weight for a given span length also has the advantage of requiring smaller crane and hauling profile STATE ROUTE 162/6 PUYALLUP RIVER BRIDGE / PIERCE COUNTY, WASHINGTON BRIDGE DESIGN ENGINEER: Washington State Department of Transportation, Tumwater, Wash. PRIME CONTRACTOR: Selby Bridge Company Inc., Vancouver, Wash. PRECASTER: Concrete Technology Corporation, Tacoma, Wash.—a PCI-certified producer LIGHTWEIGHT AGGREGATE SUPPLIER: Carolina Stalite Company, Salisbury, N.C. State Route 162/6 existing historical concrete pony truss bridge that was replaced. Photo: Washington State Department of Transportation. Prestressed lightweight concrete girders were used for the new bridge. Photo: Washington State Department of Transportation. S R 1 6 2 / 6 i i h i i l b i d by David Chapman, Concrete Technology Corporation, and Eric Schultz and Bijan Khaleghi, Washington State Department of Transportation State Route 162/6 Puyallup River Bridge Successful bridge replacement in Washington State using prestressed, lightweight concrete girder superstructure 18 | ASPIRE Summer 2016 P R O J E C T