Washington State is home to a wide variety of bridge designs that not only connect communities but also showcase the ingenuity of civil and structural engineering. In this post, we’ll explore several bridge examples in Washington, categorized by bridge type, and provide insights into the work of a bridge engineer behind these structures.
Truss Bridges
Truss bridges are among the earliest modern bridge designs, known for their strong triangular frameworks that efficiently distribute loads.
- Example: I-5 Bridge over the Columbia River (Interstate Bridge)
- Location: Vancouver, WA to Portland, OR
- Type: Through Truss
- Year Opened: 1917 (Northbound Span), 1958 (Southbound Span)
Only the northbound span (1917) is a truss bridge; the southbound span (1958) is a concrete segmental box girder. A bridge engineer working on such projects must account for stress distribution and fatigue in the steel components while preserving safety standards and traffic flow.
Arch Bridges
Arch bridges use a curved structure to bear weight, typically constructed from stone, steel, or concrete.
- Example: Montlake Bridge
- Location: Seattle, WA
- Type: Bascule Arch (Movable)
- Year Opened: 1925
Arch bridges require careful planning from bridge engineers to ensure the forces are correctly transferred through the abutments into the ground.
Suspension Bridges
Suspension bridges use cables suspended from tall towers to support the bridge deck, allowing for long spans and flexibility.
- Example: Tacoma Narrows Bridge
- Location: Tacoma, WA
- Type: Suspension
- Year Opened: 1950 (Westbound), 2007 (Eastbound)
The current Tacoma Narrows Bridges replaced the infamous “Galloping Gertie,” which collapsed in 1940 due to aeroelastic flutter. Suspension bridges are among the most challenging for a bridge engineer, as they must consider wind dynamics, cable tension, and seismic activity.
Cantilever Bridges
Cantilever bridges extend structures horizontally and are supported at only one end. They are ideal for long spans without needing falsework in the middle.
- Example: Columbia River Railroad Bridge (BNSF Bridge 9.6)
- Location: Vancouver, WA
- Type: Cantilever Truss
- Year Opened: 1908
Used primarily for freight trains, this bridge demonstrates a steel cantilever design, where large arms reach out over the river and support a central suspended span. Cantilever bridge design challenges a bridge engineer to handle immense balancing forces and manage tension/compression zones carefully.
Cable-Stayed Bridges
Cable-stayed bridges feature one or more towers with cables running directly to the deck, forming a fan or harp-like pattern.
- Example: Sr 520 Floating Bridge (with Cable-Stayed Section)
- Location: Seattle to Medina, WA
- Type: Floating with Cable-Stayed Ramp
- Year Opened: 2016
While the main portion is a floating bridge, the east and west approach ramps include cable-stayed sections for added stability and aesthetic appeal. A bridge engineer working on a cable-stayed bridge must balance cable tension and tower forces, particularly in areas prone to seismic activity, like Washington.