146-Ft Long Precast Prestressed Bridge Girders in Washington State

T longest precast prestressed concrete bridge girders (Fig. 1) ever used for a Washington State Department of Transportation highway project are being incorporated into the Coweman River Bridges near Longview, in southwest Washington. Currently being constructed, the four bridges are part of a realignment of Interstate 5 that will shift the highway away from a slide-prone area which has created traffic hazards over the years. In order to bypass the hazardous rock bluffs of the slide area, the new section of highway crosses the Coweman River on parallel bridges in two places. Four bridge spans of 140 to 146 ft (42.7 to 44.5 m) were required to cross the river within the newly allotted section of highway right-of-way. Although prestressed concrete has long been recognized as a preferred construction material in the State of Washington, the bridge designers were concerned about the cost of such unusually long-span girders. Therefore, the designers prepared detailed cost estimates for precast prestressed concrete girders with a field-cast deck versus a cast-in-place concrete box girder structure. After comparing these estimates, superstructures using the Washington State Department of Transportation standard I-girders (Fig. 2) were chosen.