I-84: Lower Perry Interchange Repair
Owner: Oregon Department of Transportation
Contractor: Oregon State Bridge Construction
Project Location: La Grande, Oregon
Engineering Service: Bridge Engineering
The Lower Perry bridge repair was part of a traffic safety improvement project west of La Grande, OR. Safety improvement of this particular bridge involved correcting of a superelevation in the wrong direction. The contract plans sent out to bid called for reversing the superelevation by removing the deck from the Bulb T girders, jacking the girders to the new grades, re-pouring the beam seats, and re-pouring the deck. This plan proved hard to construct and lacked the proper permits to be successful. McGee Engineering was hired by the contractor to develop an alternate design that could be constructed in the timeframe allowed.
Many design options were considered and in the end we came up with an innovative design that involved rebuilding the existing girders in place to provide the appropriate superelevation. The rebuilding process required removing the deck and girder flanges, extending each of girder webs and pouring a new deck. To achieve the proper superelevation and maintain a consistent deck thickness, the web extensions varied in height for each girder across the span. This required extensive analysis to ensure that the prestressed girders would maintain sufficient strength after reconstruction. By varying the girder depth across the span in this manner, typical AASHTO distribution factors did not apply and McGee Engineering had to justify revised distribution factors through the use of finite element analysis and spring supported deck beam models.
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