The Twisp River Bridge is one of the first applications of the use of the WSDOT "super girders" that were developed in the late 1990's. Constructed with spliced post-tensioned I-girders, this bridge provides a clear span across the Twisp River in the north-central region of Washington State.
The 95" deep x 196' long girders, assembled from three pieces of 44.63', 101.39', and 44.63', were supported on temporary shoring over the river while closure pours were cast in the joints between each piece. The cast-in-place deck was then constructed and the girders were post-tensioned.
Spliced construction was chosen for the girders because the remote site location precluded transporting single-piece girders of that length and weight (235,000 lbs).
Long Span - Long span design presents minimal interference with river flows and fish habitat.
Spliced Construction - Spliced construction allowed a long span bridge to be constructed in a remote location.
This article provides details of the design and construction of the Twisp River Bridge, a 60m (197 ft) long single-span bridge in the North Cascade Mountains in Washington State.