General Contractor Hamilton Construction Co.

Structural Engineering David Evans and Associates Inc.

The $56.5-million I- 84 Sandy River and Jordan Road bridges project is located along one of the Northwest’s busiest interstate freight routes. Two 840-ftbridges were replaced with longerspan steel- tub girder structures on the preexisting alignment. Through construction, there was a temporary detour bridge for I- 84 traffic.

Environmental concerns required rigid debris containment structures under the original bridges and construction of access trestles to keep equipment out of the river. Modeling programs revealed that a traditional work bridge approach would hang up debris during high water events and cause flooding risk. The team decided on a modified gantry crane solution that launched the 165-ft steel girders from the shore, shav- tening almost five years off the project schedule. As part of this solution, Hamilton Construction removed the work bridge it had already built in the 6-week in-water season and purchased and modified a pair of 250,000-lb lift capacity gantry cranes each weighing 100 tons. These gantry cranes spanned the 90-ft-long superstructure and ran along a track that allowed for placement of the steel tub girders from the top down. The gantry system’s support structure cut the need for piles in the river to 12 from 100. The wider spans between the piles reduced the chance for debris and water to back up.

Steel beam sections, sized for delivery through narrow city streets and bolted together by the crews, were launched by the cranes moving along tracks located on the detour bridge.