Alaska Railroad Corporation - Planning, Design Construction of the Tanana River Bridge

摘要

Long term plans for rail expansion, partnered with needs for year round access to military training grounds in the interior of Alaska, resulted in the longest bridge in our country's largest state. Planning activities for this 3,300 ft. bi-modal structure over the Tanana River included an alignment study with federal review of environmental impacts, partnering with the military for funding assistance and establishing a contracting approach utilizing the CM/GC process. The superstructure design effort was challenged to solve the requirement for shared use of the bridge by highway or rail vehicles. The presence of large woody debris up to 90 ft long with a 9 ft root ball caused high design loads and deep scour on the substructure. Lower level flood events combined with ice jams provided yet another design load case that was outside those typically experienced. The scour design activities went as far as analyzing a scaled model of the foundation piers and woody debris in a hydrosystems lab with river soils replaced by walnut shells. Bridge construction planning & scheduling was governed by severe cold weather in the winter and ice breakup followed by high river levels in the spring & summer. The decision by the owner to accept the use of structural steel fabricated in China allowed the project to proceed within the budget allocated. The final product was found to be of high quality.