R&M Through the Years: Anchorage Bike Trail and Pedestrian Bridges
March 13, 2019
In celebration of R&M’s 50th anniversary, we are taking a look back at the projects over the last five decades that made R&M into the firm it is today. This month we take a look at several bridge structures in the Anchorage area designed by R&M in the late 1970s.
R&M has always believed strongly in the importance of pedestrian and bicycle facilities. In our early years, we designed several bike and pedestrian infrastructure facilities that are still used by Anchorage residents year-round. This includes numerous pedestrian bridges on the Campbell Creek trail and crossing Northern Lights Boulevard.
Campbell Creek Trail Bike and Pedestrian Bridges
The Campbell Creek multi-use greenbelt trail was developed as a safe means of access to a large portion of the Anchorage bowl and Campbell Creek Watershed, providing access to many recreational opportunities for the Anchorage community. As part of the trail development, R&M provided design and construction inspection services for five bike and pedestrian bridges and their associated bike path approaches.
The bridges were made of press treated glue-laminated wood to maximize economies and aesthetically fit into the surrounding natural areas. These bridges were of various lengths with one structure spanning as much as 80’ over Campbell Creek. R&M determined the best stream crossing locations for these structures and then designed the bike path approaches to them. Efforts included establishing the best geometrical layout of the bridge approaches, as well as determining the proper depth of gravel materials required for local soil conditions. Gravel quantity estimates were also made. The design was prepared in a “fast-track” effort that lasted less than one month.
Northern Lights Boulevard Pedestrian Overcrossings
Due to the close proximity of Rogers Park Elementary School and residential neighborhoods, several pedestrian crossings were needed to span the Northern Lights/Benson arterial couplet to create a safe route for pedestrian and bicyclists in the area. R&M designed three unique, all-timber pedestrian bridges to meet that need. Architectural compatibility, engineering economy, and minimum disturbance to the natural trees and ground cover were a must when developing the overcrossing designs.
R&M chose naturally finished wood as the predominant structural element to achieve a natural look that blended with the neighborhood setting and would minimize future maintenance problems.
In addition to providing a stairway system, the stair towers function as foundations for the structures. A compact configuration avoided interference with above and below ground utilities, as well as disturbance of natural vegetation.
A truss bridge spans 130’ in one location, while twin 90’ spans were used on two branches of the couplet at another site. Roof and deck diaphragms that provide lateral stiffness and resistance to buckling permitted assembly of the bridge units at ground level. They were subsequently hoisted by crane into position on the foundation towers.
Next month, we move into the 1980s to look at several hydroelectric projects in which R&M helped determine the engineering and economic feasibility of hydroelectric development.