Friday, January 16, 2015

Building a bridge on top of a bridge

by Bart Treece

Traffic has returned to the State Route 508 South Fork Newaukum River Bridge near Onalaska in Lewis County. For the safety of the public, WSDOT crews closed the bridge Sunday, Jan. 11. Since then, WSDOT maintenance crews were busy building a temporary “Bailey” bridge over the existing structure.





The bridge was weight-restricted in 2012 because heavy loads put additional stress on aging steel truss members.



Bailey bridges were first used by Allied forces during World War II to move heavy equipment, like Sherman tanks, over rivers and ravines. Instead of troops in green fatigues, WSDOT maintenance outfitted in safety orange vests and yellow hard hats worked like a small army to assemble pieces of the bridge. Each part moved into place by hand and was fastened together. Once assembled, the crews slid the Bailey bridge into place using a series of rollers.



The SR 508 Newaukum River Bridge is essentially two separate spans. Part of the bridge is steel, which as you can tell by the rusted I-beam in this photo, is deteriorating.



The other part is supported by timber, which is still in decent shape and safe to use. We only had enough bridge deck to span the steel portion of the existing structure, and it would take an additional three months to acquire more pieces. The solution was to span the Bailey over the steel sections and reinforce the timber piers. To do this, we used hydraulic jacks to lift the bridge half an inch to slide in new pieces of steel. This also allows for legal loads to again use this route.



Crews built ramps to the Bailey on Tuesday, Jan. 20. Before the temporary bridge was opened to travel on Wednesday, Jan. 21, barrier and striping work was completed.



All of this makes the most of the available resources, and will allow traffic to move safely across the bridge until the new structure is completed in 2018.