Interstate 5 Skagit River Bridge Replacement

The Interstate 5 Skagit River Bridge in Washington State required emergency replacement after a truss span collapsed when struck by an over-height vehicle. The replacement structure was designed and constructed on an accelerated schedule to restore traffic on this critical interstate corridor north of Seattle.

To meet strict weight limitations and allow rapid installation of long-span girders, the design-build team selected prestressed concrete girders produced with structural lightweight concrete made using Stalite Lightweight Aggregate. The lightweight concrete reduced the overall weight of the girders while maintaining the high compressive strength required for long-span bridge construction.

The replacement span utilized prestressed concrete girders with compressive strengths approaching 9 ksi while maintaining a fresh density of approximately 123 pcf. The reduced unit weight allowed the girders to meet transportation and lifting requirements while improving structural efficiency.

Using Stalite Lightweight Aggregate enabled the design team to achieve the required strength while limiting dead load, allowing the permanent replacement span to be constructed quickly and safely while meeting strict structural and transportation constraints.