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April 14, 2016
The state Route 520 Floating Bridge Maintenance Facility is a 19,600-square-foot, four-story building designed to support the maintenance needs of the new floating bridge across Lake Washington. Because of its location, tucked under the east side bridge span, and unique requirements, the project resulted in an unusual and interesting facility design.
The building’s primary role is to serve as the nerve center of the bridge, which includes communications, maintenance and emergency response functions. The facility staff maintain the floating pontoons that form the bridge’s structural base. All sensors come into the reporting system inside the maintenance facility, which relays this data to multiple monitoring locations for the Washington State Department of Transportation.
One of the challenges of this project was the site. Located directly below the bridge on the east shoreline, it is embedded in a very steep hillside with a vertical distance of 45 feet between the shop level and the parking/entrance level.
Vehicle access is provided from Evergreen Point Road by a steep driveway leading to an enclosed parking lot below the bridge. Vehicle access to the water is not possible at this location, so all materials, equipment and personnel for bridge maintenance must come down through the four-story building via high-speed freight and passenger elevators.
The placement of the elevator was carefully designed to reduce the time required for emergency responses. Minutes matter tremendously in an emergency situation, so the design and function of this elevator was a crucial part of the project. The freight elevator has a capacity of 14,000 pounds and stops at the storage mezzanine and covered shop yard for direct access to both the shop and dock at all times.
The appearance of the facility was also an important factor in the project design. The site is located in a residential area of the city of Medina, so it was important to consider the impact to the neighbors and local community.
The design intention was to blend the building in with the hillside and make a connection with the local community. Materials were selected, and building detailing was designed, to give the building residential cues when viewed from the water, rather than a maintenance facility or utility component of the bridge structure.
Natural colors were chosen to help tie the building in with the colors of the hillside and surrounding landscape. The access drive to the facility includes 30-foot-high concrete walls designed as a natural earth embankment, which was achieved through concrete sculpting and staining techniques.
The concept of an enclosed building was a key component to the design and appearance of this facility to ensure that no clutter would be visible on the property from the lake or neighbors. It also helps to minimize noise and light impacts to the neighbors, and protects staff from inclement weather.
Although the exterior is designed to appear more residential, the interior features strong, durable materials designed for longevity and low maintenance, including heavy-duty epoxy flooring.
The administrative level of the building has a full-width, frontal view of the bridge, which is designed to guarantee that staff can visually monitor the bridge from any location on this level. The windows include bullet-resistant glazing for staff safety, and to allow the windows to remain operational under all circumstances. The building is isolated from seismic events by a large retaining wall, which creates a 5-foot gap around the building and has an emergency generator backup in case of power outage.
A dock for fueling and servicing the maintenance vessel is located approximately 110 feet below the bridge deck and is connected to the maintenance facility by a sloping access pier.
The access pier is designed to let daylight shine through the center of the bridge to prevent shading of fish habitat on the shoreline. The lighting on the pier was also chosen to have low impact on neighboring houses.
The shoreline will be restored, and the site will be landscaped to blend with the surrounding vegetation and return to its native state.
Lowell Cate is a principal architect with Helix Design Group with over 29 years of experience. He served as principal architect for the new SR 520 Floating Bridge Maintenance Facility.