58 in. tall prestressed girders precast with 49-in.-wide top flanges maximize span length, minimize the number of girders and allow clearance above the river for a 100-year flood.
As part of the Lincoln County Bridge Replacement Program, Oldcastle Precast of Spokane, Wash., fabricated 136.8-ft.-long prestressed concrete super girders for the new Miles Creston Bridge in Lincoln County, Wash.
The term “super girder” resulted from the efficient shape of this new bridge girder family, which utilizes high strength concrete and .6-in.-diameter prestress strand to maximize span length and minimize the number of girders.
The Lincoln County Public Works Department worked with consultant Nicholls/Kovich Engineers of Spokane, Wash., on the project. Nicholls/Kovich specified WSDOT WF 58 optimized super girders for the replacement of the existing Miles Creston Road Bridge Over Hawk Creek, due to its substandard load capacity, thus requiring a high-priority replacement bridge.
General contractor Wesslen Construction, Spokane, Wash., the low bidder on the project, awarded Oldcastle Precast-Spokane the contract to manufacture and haul the wide-flange super girders for the new Miles Creston Bridge.
At 125,438-lb. each, Oldcastle Precast manufactured five, wide flange super-girder bridge beams, measuring 58 in. tall by 136.8 ft. long. The girders were used to build the bridge superstructure, with a conventional cast-in-place concrete deck.
The girders’ 49-in.-wide top flange and 38-in.-wide bottom bulb give much more lateral stability during transport than the shapes they replaced, and a much larger prestress force increases spans to minimize the quantity of girders required. In this case, spanning 136.8 ft. with only a 58-in. depth of girder provides an aesthetically pleasing profile as well as providing adequate clearance above the river for a 100-year flood.
Each super girder is custom manufactured in Spokane and transported on trucks specially designed to hold the weight. Due to their size, the girders must be transported to the construction site on steerable rear supports. Once the girders arrive on site, crews used two cranes to set them on top of the new bridge abutments.
“Using long-span precast, prestressed concrete girders can eliminate the need for falsework, reduce on-site construction activities and schedules, reduce environmental impacts at water crossings, and minimize hazards, delays and inconvenience to the traveling public,” said Oldcastle Precast Sales Manager Chuck Prussack.
Precast, prestressed concrete girders have proven economical and durable across the U.S. for more than 65 years. As one of the leaders in the use of the new optimized girder shapes, the Northwest has been using the super-girder shape at a 100-in. depth on spans more than 200-ft. for many projects, with many more structures in this span range being designed.
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