The Design Story of Edmonton’s New Walterdale Bridge
It’s hard to believe now, but replacing Walterdale Bridge wasn’t planned to be anything special. So how did we go from a standard replacement bridge to a new icon that redefined the whole city?
The original Walterdale Bridge was approaching the end of its life, and needed to be replaced. At first, the City of Edmonton was interested in a fairly pragmatic girder bridge replacement.
DIALOG saw this as an opportunity for so much more.
DIALOG had been working on an EXPO bid with the City of Edmonton. The flats on the north side of the bridge and the river crossing were planned to be one of the main sites of the event. We were very familiar with the area through our concurrent work on West Rossdale Urban Design Plan.
Though the City didn’t end up bidding on EXPO after all, this planted a seed in everyone’s mind about the powerful potential of a new bridge in that area.
This was around the same time Edmonton’s former mayor, Stephen Mandel, famously called for “no more crap” when it comes to design in our city. The timing was right for DIALOG to point out the opportunity for a better bridge. City Council agreed.
DIALOG prepared four bridge type options for the City of Edmonton to share with the public. After consultation with stakeholders was complete, the majority liked the arch bridge concept best.
From there, DIALOG explored the styles of arch bridges that would be possible at a range of budgets. After considering the project constraints, aesthetics, integration into the urban environment and input from the public, the through-arch structure with the curved shared use path to the east was recommended.
The selected design is a gracious, single span, twin through-arch steel structure, spanning 206 m (greater than the length of two football fields) from bank to bank across the North Saskatchewan River. It carries three lanes of northbound vehicle traffic, a sidewalk to the west of the roadway and a separated footbridge or shared-use path for pedestrians and cyclists to the east.
The area on the northeast side of the bridge has significant historic and cultural importance. There is the Traditional Burial Grounds/Fort Edmonton Cemetery which includes a memory circle, re-interment area and historic graveyard. The roads and new bridge were carefully realigned to keep the existing structure open to traffic during construction, while respecting the historical site constraints.
The structure is an engineering marvel. The Edmonton Journal used analogies to describe it:
The physics involved might make engineering students shudder. Think of it: steel cables thicker than your fist stretched by several inches as crews poured the concrete deck. Steel arches bent into a target shape as the cables were tightened one by one, like tightening spokes to shape a bike wheel. Korean steel fabricators… didn’t just deliver 125-tonne puzzle pieces, they delivered 42 pieces deliberately misshapen so the forces within the bridge could form it into the right geometry.
The new Walterdale Bridge is one of the most complex infrastructure projects ever completed in Edmonton. Not only was it a complicated bridge to engineer, the construction was also incredibly challenging.
EXCAVATION FOR THRUST BLOCKS
Large thrust blocks provide a foundation for the arches, which carry the bridge load. Each thrust block is made of about 600m3 of concrete and 44 steel micropiles installed 20m below the road elevation. That’s about as deep as a six-storey parking garage. During construction, enough material was excavated from the cofferdams (temporary watertight enclosures) to fill two Olympic-sized swimming pools.
ARCH FLOAT AND LIFTS
Each arch rib is made up of 21 steel box segments with masses of up to 125 tonnes, using 1500 bolts at each connection. End and intermediate segments were erected from temporary berms extending from each river bank. Central sections were assembled on the south bank, transported, and then lifted into place in two critical lifts.
For the first lift, central sections of both arch ribs were transported onto barges, then floated into position between the berms. The central sections were lifted and connected to the intermediate segments that were already erected on the berms.
The bridge deck, supported by 32 hangers, is a steel framework supporting a cast-in-place concrete deck covered with asphalt. It used 65 tonnes of reinforcing steel and 1600m3 of concrete. The bridge currently carries three lanes of traffic, but is designed so that another lane can be added.
Nothing like this had been constructed before, and there were many complications that delayed the project. Everyone was eager to get on that fancy new bridge!
On an unassuming Monday morning, rush hour commuters approaching the river crossing were pleasantly surprised to be able to drive across the new bridge. The bridge was finally open to traffic! There was still more work to be done. Construction continued on the shared use path and trails around the bridge. The old bridge had to be deconstructed, too.
Even though the project wasn’t complete yet, Edmontonians were already falling in love with their new bridge. Everyone seemed to forget about the delays once they could feel the height of the arches as they drove below them. The bridge announces you have arrived downtown, and frames views of the city and valley as you approach.
With the old bridge taken down and the trails and landscaping finished, the whole project was complete.
SHARED USE PATH
The shared use path bridge is one of a kind. Sharing the eastern arch but separated from traffic, it is designed for people to enjoy crossing and lingering. Benches with high backs help reduce traffic noise and soften prevailing winds. At each end, the path is about twice as wide as it is in the middle, gracefully connecting with the valley.
The shared use path bridge is made up of 25 steel segments installed in 11 sections. It is supported by 14 hangers that connect to the east arch of the main bridge and delta piers at each end.
Trails below and around the bridge are part of the city’s 160km river valley trail system. People no longer need to cross traffic to continue along the trails in any direction. With less than 5% grade, all paved paths are fully accessible. On the north side, a promenade encourages people to slow down and take in the views of nature, like looking out from a balcony.
At the abutments, the grade change from the bridge to the riverbank is acknowledged with sweeping gabion walls and intensive plantings. Evocative land form and planting reinforce the signature quality of the bridge. The gabion walls provide seating opportunities where they edge the plazas and paths.
Under the bridge, the high water levels during historic flood years are noted on the abutments. Visitors will notice there are fewer marked on the north side because the elevation of the north bank is higher.
In only its first year, Walterdale Bridge quickly became the new defining icon for the city. The bridge is the focal point for postcard views of Edmonton, and photographers have flocked to it, both day and night.
Beyond providing a refreshed visual identity for Edmonton, Walterdale Bridge creates a prominent public space where the duality of the city and nature are experienced and celebrated at a pivotal location. Crossing the river is now enjoyable for all modes.
Edmontonians have embraced it as a point of pride, highlight in their daily commute, and backdrop for meaningful moments. It will continue to define the city for decades to come.
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