NEW SPAN RECORD FOR PRECAST GIRDERS Douglas Sarkkinen, PE, SE, Otak, Inc. Vancouver, WA
The recently completed Chandler Road Bridge over the Chehalis River in Lewis County, WA solves a critical problem for the owner, that is, replacing a bridge that was destroyed in a flood with a new structure that is robust in terms of impact resistance, durable, economical and can clear span the river so debris will not hang up on center piers during future floods. The solution? Precast concrete. A bridge utilizing the new 95 inch deep post-tensioned WSDOT precast girders that is 240 feet long, setting the record for a single span precast girder bridge in the State of Washington.
The existing three-span cast-in-place Chandler Road Bridge, destroyed in the December 2006 Chehalis River flood, was located at a bend in the river and had the foundations undermined and the entire superstructure was swept downstream. The replacement design had several challenges: not only raising the structure to maintain clearances and requiring a clear span, but a robust structure that could withstand lateral impact from large trees or rootwads that float down the river during a flood. This paper discusses the design of the replacement structure starting from bridge selection to final design, including challenges involved with calculating the expected deflections and creep. Additionally, the paper covers the bidding and construction phase, including issues during the shop drawing review with the girders and post-tensioning, and the unique method of erection devised by the contractor. Incidental issues with concrete strengths at the closure pours had to be dealt with during critical portions of the project. Lastly, a brief discussion of the long term deflection monitoring is included.
This paper gives an inside view of the challenges and issues associated with the project, yet also demonstrates how precast concrete has been taken to the “next” level by use of the large girders and post-tensioning splice methods.