SOLUTION

A precision survey and other field measurements were performed prior to each repair project to determine the position of the bridge trunnions, racks, pinions, and pinion shafts. A mechanical review was carried out to evaluate various options to address the machinery misalignments and to improve the functionality of both rack and pinion systems on the west leaf. The team provided drawings and specifications for both projects.

Seeking a temporary repair during the first project, CDOT elected to remove and refurbish the existing rack segments and reinstall them using the existing alignment with new special pinions. Following approximately five years of normal operation, wear of the new south pinion teeth began to cause operational issues. After conducting new field measurements and a precision survey, the project team recommended options to further improve the mesh of the north and south rack and pinion systems. For the second project, the final design required both existing pinions to be modified to restore the original gear tooth profile. All rack segments were removed and repositioned to restore an optimal radial alignment. A new system of structural rack side plates was installed to facilitate the realignment work. Other structural and mechanical engineering design and component installation challenges were overcome, and the bridge was successfully returned to service.