V+M is the designer and Engineer of Record for the White River Bridge, a key link in the regional Foothills Trail extending 48km through communities and scenic landscapes in the shadow of Mount Rainier. The footbridge is now a regional destination where people of all ages and abilities can linger over the beautiful White River. It also provides a secondary route for emergency vehicles in the event the nearby roadway crossing is impaired.

Existing concrete wall piers at the new crossing supported a former road bridge (c.1910). Upon investigation of the piers, it was found no reinforcement was present, necessitating retrofit measures to upgrade them for seismic performance.

The total bridge length of 187m includes three arch spans and an approach span. Network tied arches are used for the crossing to create a highly transparent structure that is at the same time very stiff. The crisscrossing hanger pattern is capable of carrying heavy point loads from a fire truck without distressing members or causing significant deflection.

Aesthetic considerations were important and V+M’s designers skillfully created a structurally expressive form with cohesive design elements like the overhead bracing, “sky light” gaps between the concrete deck and arches to limit shading on the water, and implementation of generous lookouts at the central pier to provide users an area to linger and take in views of the river. All this was achieved while:

• Avoiding in-water works;
  
• Minimizing use of materials;
  
• Minimizing maintenance through use of weathering steel, concrete and FRP grating; and
• Minimizing construction costs through fabrication-friendly detailing and utilization of standard sections wherever possible.

V+M prepared the structural plans, specifications, and estimate for the bridge and provided construction administration services. V+M also created renderings of the bridge during the early stages of design to support outreach and stakeholder engagement efforts.

Design proceeded with only 2 back-to-back arches supported on century-old wall piers. However, in the middle of design, permitting requirement changed and necessitated adding a third arch span. The piers were retrofit to support this new crossing, with a 5m wide deck and total length of 187m. The center span crosses the current White River, but the river channel is expected to migrate north over time into the third span. Our creative solution was to remove the wall at the north pier, leaving the footing and installing drilled shafts through the footing to ensure capacity with scour.

Environmental stewardship is an essential aspect of this project with 60,000 migrating salmon traveling up the river daily during spawning season. Consultation with the Muckleshoot Indian Tribe resulted in the removal of 2500 m3 of riprap along the river shore as salmon habitat enhancement. The openness of the structure and gaps between the deck edge and tie chord help to reduce shading effects on the aquatic habitat below. Weathering and stainless steel were selected to avoid deleterious materials over the water and to ensure longevity. Lookouts added to the central pier allows users to take in views of the river and landscape.

Design of the arch spans optimized the hanger pattern and focused on fabrication and construction ease. Seismic design uses base isolation of the superstructure atop the supporting piers to accommodate major earthquake demands without damage.

The new gateway bridge provides a key crossing of the White River. New foundation elements avoided restricted and below highwater areas. Refurbished existing bridge piers are retrofit with supplemental deep foundations, and base isolation of the new arch spans limit seismic demands on the substructure.