Staircase Rapids Trail Bridge Olympic National Park, Washington

To enhance user experiences at Olympic National Park in northwest Washington, this 210-foot pedestrian bridge was designed as an integral component of the trail system near Staircase Rapids. With a design-build delivery method, Otak led the survey, engineering analysis, and ensuing design for the project through construction using unique approaches with partners to accommodate the site’s isolated location.

A Design-Build Structure for a Scenic Trail Site

Spanning the Skokomish River, the Staircase Rapids Trail Bridge is a steel-framed suspension bridge in an old growth area of the Pacific Northwest. The design included a detailed analysis of vibration with the bridge span due to pedestrian footfall. A computer model of the bridge was compiled and subjected to a battery of dynamic pedestrian loads. A physical model of the bridge was also constructed to model the oscillations and allow the bridge designers to gauge their impact. These findings led to the inclusion of a passive tuned mass damper – consisting of steel plates suspended on a spring – to reduce vibrations on the bridge and enhance the user experience. The dampers were adjusted through field tests and measurements of the bridge dynamics near the end of construction. Because the project’s location in a wilderness area, all equipment and materials were flown in via helicopter. During construction, two temporary bridges were installed to allow the contractor access from one side of the river to the other. When construction finished, the temporary bridges were flown out along with equipment and unused materials.