A Thoughtful Approach to Active Transportation Structures
As society and our industry strive toward largely common goals such as meeting emission targets, speeding pandemic recovery, and simply making our cities great places to live, work, and play, developing Active Transportation networks has become a key initiative for governments and other caretakers of the public realm.
At Entuitive, we are always excited to contribute our bridge engineering expertise to making Active Transportation development a reality. In this article, we’ll review the mainstays of our approach and how these translate into action, with several of our recent projects serving as examples.
Achieving Design Excellence
Entuitive’s transportation group is a design-driven team of specialists with a long history of successful collaboration on iconic, high-profile transportation projects across Canada. Our design on active transportation infrastructure projects, which includes the successful delivery of over twenty pedestrian bridges, addresses all stages of the asset lifecycle to achieve optimal return on investment, from the earliest concept to end of life or renewal.
The depth and breadth of our experience, integrating structural, bridge, and construction engineering, translates to a deep understanding of how creative solutions, coupled with a focus on outcomes, can make a project successful. Our client-centric approach helps to ensure we meet client needs without sacrificing function or constructability in the design, truly providing the best value for the community.
Our expertise on hundreds of bridge projects enables our team to present several design options. We explore numerous structural alternatives to meet the constraints of a site and to achieve the clients’ design aspirations. These design aspirations naturally range from purely cost-driven, to situations where visual impact of the bridge takes precedence. Our work has taught us that aesthetics is about the right structure for the context, be it a series of simple repetitive park bridges or spectacular and iconic structures that become the symbol of the community they serve.
A Context-Sensitive Approach to Placemaking
Our bridge team considers the aesthetic impact of a structure within its context. This context can include the natural environment, heritage and cultural considerations, existing trails or other modes of transportation with which the bridge will connect; physical and temporal constraints on construction work; and budget limitations. Our goal is always to work within the specific context of the project to design a bridge that cooperates with its physical surroundings to create a sense of place, and that adds utility, accessibility, and, hopefully, a touch of joy to a user’s travels.
Through our work rehabilitating and demolishing existing bridges, we see how physical deterioration impacts both the function and aesthetics of a bridge over time. We also see how evolving architectural styles can change the way a bridge is perceived by the community it is situated in. Whether the project aims to create a signature bridge or a utilitarian crossing, these insights allow us to help our clients build bridges that will retain their aesthetic merit throughout their service life.
Context Sensitivity in Action at Milne Creek Bridge
The Milne Creek Bridge is a 58m, single span, cable-stayed bridge spanning Milne Creek, a tributary to the Rouge River in Markham, Canada. The site is a shallow valley with a braided wetland stream with extremely high environmental sensitivity.
The design of the Milne Creek Bridge worked within these constraints, taking the path from bank to bank without touching the braided stream, and lifting the path to the tree canopy in the process. The bridge itself has a wood deck and weathering steel railing. Only small cranes could be used for bridge erection, so the bridge was designed to be constructed outwards from the abutments. Its twin girder steel superstructure is supported by bridge strand stays that are deviated at steel towers positioned on the abutments. The result is a treetop walk with the structure barely there.
Collaborating with Clients and Partners to Deliver Value
As structural engineers, we work tirelessly to develop and maintain our industry-leading technical expertise. We also recognize that the purpose of our structures is to serve the broader aims of the project. We seek collaboration with our clients and partners, engaging with the full team to understand their goals and requirements, be they functional, aesthetic, or budgetary. We are always looking for ways to ensure our bridge design can contribute positively to realizing those goals.
We know that good ideas, including those directly related to the structure, can come from any contributor in the design process – owner, architect, other consultants, peer reviewers, or the public. Building out a design progressively with open dialog is our standard approach.
Collaboration in Action at Highway 7/8 Cycling and Pedestrian Bridge
An example of this type of collaboration in action is our design for Highway 7/8 Cycling and Pedestrian Bridge, a 53 m bridge to be constructed in Kitchener-Waterloo in Summer 2022. The bridge crosses a provincial highway in the city, connecting the communities North of the highway to a transit station to the South. Our client, the Region of Waterloo, wanted to provide an efficient connection across the highway in the form of a structure which would be viewed as a positive aesthetic addition to their cityscape while also providing an active transportation link.
As part of the Environmental Assessment process, our team developed several strong and distinct design concepts with municipal, provincial, transit and environmental stakeholders, before holding public consultations to solicit input from the local community. A single-span steel through truss was selected as the best concept in terms of aesthetics, user comfort, constructability, and economy. The selection process deliberately included discussion of the pros and cons of each potential design in a balanced, unbiased manner, and the selected design was further evolved with the client group to truly optimize the solution. The single-span structure kept all construction out of the highway right-of-way, a preference indicated by the Ministry of Transportation Ontario (MTO). The prefabricated structure allowed for most of the construction to occur offsite, reducing the impacts to the residential community.
The challenge with the preferred concept was that the minimum clearance above a provincial highway of a steel structure is higher because the durability is compromised by exposure to highway de-icing chemicals. Increasing the height of the structure meant increasing the lengths of the approach ramps and stairs, increasing cost and impacting the user experience.
Our solution was to collaborate with the MTO to develop a significant structural innovation: having the post-tensioned concrete deck act as the primary tension member in the truss. This innovation permitted the vertical clearance over the highway to be reduced without compromising the durability of the structure and shortened the total length of the bridge’s approach ramps by over 30 m – hugely improving the efficiency of the crossing. This innovative solution also created an opportunity to collaborate with our architectural partners, Montgomery Sisam, to design a unique structure the community could be proud of.
Our ability and willingness to innovate structurally allowed us to design a solution that met the requirements of all stakeholders.
Optimization and Construction-Driven Designs
Conventional bridge systems have well-established construction means and methods. For example, when presented with a tender for a precast concrete girder bridge over a highway, any experienced contractor can quickly assess what will be involved in the construction process and estimate an appropriate price for their bid. As discussed above, active transportation bridges often go beyond conventional approaches in response to their context.
As a design becomes more unusual, contractors must price in the risk associated with taking on work that may require unconventional erection techniques. For the project to be a success, the design consultant must be able to help manage this risk by considering construction means and methods while developing the design, clearly presenting a viable construction method in the tender documents.
Entuitive’s long experience as Construction Engineers allows us to push our designs outside the realm of what is normal while avoiding designs and details that would create untenable risk of construction delays and cost over-runs.
Optimization and Construction-Driven Designs in Action at Milne Dam Pedestrian Bridge
The Milne Dam Pedestrian Bridge is a 143 m, multi-span cable-stayed structure spanning the environmentally sensitive Rouge River in Markham, Ontario. The site is adjacent to an existing earth dam and flood control structure and is set in a wide river valley. The path leads from the top of the valley wall down to the flood plain. The goals with this bridge were to create a context-sensitive design that minimized environmental impact while serving as a placemaking landmark given its high-level setting above the Milne Dam and adjacent reservoir. Collaborating with the landscape architects Schollen & Company, the City of Markham, and with the TRCA ensured the design respected the environmentally sensitive Rouge River watershed while meeting the functional and aesthetics goals of the project.
Conceived as a “zip line to the valley floor”, the design replaced an original plan for a long stair flight that would have broken the trail accessibility. The 45 m main span crosses above the Milne Dam and features a fanned cable design, with architecturally tapered steel pylons founded over 20m below the cable anchor points. The twin-girder steel superstructure was detailed for modularity and prefabricated into segments to lessen the erection difficulties on a site with limited access. The design used precast concrete deck panels to accelerate construction and improve both structure vibration and traction on the long sloping surface. the bridge’s height and openness give users a sense of “flying high” above the dam. Views stretch both downstream to the valley and upstream to the dam and the reservoir beyond. Viewing points and rest areas were incorporated in the bridge to take full advantage of this opportunity.
The structure provided a significant improvement to the initial design, crucially eliminating a major break in accessibility for the trail network. It has also become a symbol of the park, a clear endorsement of its placemaking ability. This was achieved within the overall budget for the trail project. It is a project that delivers on value in the broad sense, not only cost.
Active Transportation Bridges can be key to making or unlocking a place – it can bring a community to life, help drive home the value of a natural setting, and ensure a sustainable future. If you’re interested in learning more about these bridges, reach out to Stephen Brown, Jonathan Werner, Andrew Lehan, or David Hubbell.