Canadian Consulting Engineer
Award of Excellence: Esplanade RielEngineering
The Provencher Paired Bridges across the Red River in Winnipeg replace an existing 80-year-old bridge that was at the end of its useful service life. Following a two-year public consultation process, the city decided that the replacement crossing...
The Provencher Paired Bridges across the Red River in Winnipeg replace an existing 80-year-old bridge that was at the end of its useful service life. Following a two-year public consultation process, the city decided that the replacement crossing would be a four-lane vehicular bridge and a separate suspended pedestrian bridge.
The pedestrian bridge, Esplanade Riel, named after the 19th-century Metis leader, Louis Riel, was constructed during the second half of the project. It reestablishes the historic alignment of Winnipeg’s grand boulevard, Broadway, on the west side of the river, and Provencher Boulevard to the east, connecting the city’s historic French Quarter and the Forks.
The bridge is a 200-m long, 5-m wide cable-stayed structure. Its signature feature is a 57-m high single pylon, which is transversely inclined. The pier for the pylon aligns with the most westerly pier of the vehicular bridge to maintain the navigation requirements of the Red River. As a result, the pedestrian bridge spans are asymmetrical, with west and east spans of approximately 90 metres and 110 metres respectively.
Surrounding the pylon is a unique feature: a 385-m2 semi-circular plaza, which is incorporated into the design of the whole bridge.
Since Esplanade Riel is to be a place of gathering, not just a means of crossing the river, careful consideration had to be given to bridge deck vibrations. After the recent problems at the Millennium Bridge in London, U.K. with human induced vibrations, it was imperative that Esplanade Riel be designed using a rigid deck system.
Together with RWDI, the wind tunnel subconsultant, Wardrop investigated over 30 different cross-sections before the final section was determined and tested for aerodynamic characteristics. A 1:60 scale aeroelastic model was constructed to help ensure that the selected structure is stable.
Wind tunnel testing considered the construction sequencing of the bridge, as well as studying the bridge as fully erected. RWDI and Wardrop together performed an analysis of human induced vibrations.
Plaza and pilon
The designers had to be innovative to deal with the massive unbalanced moments at the base of the pylon. The entire bridge deck weight, as well as pedestrian loading, is carried by the stays to the top of the pylon. The pylon then transfers this load to the foundation. The inclination, as well as the asymmetrical spans, results in significant unbalanced moments in two directions at the base of the pylon.
The weight of the centre plaza offsets approximately 25% of the unbalanced transverse moment on the pylon caused by the bridge deck. To further minimize the unbalanced moment, the designers decided to incorporate two of the plaza stays as pylon balance stays. These twin stays are connected near the top of the pylon and to the centre support beam of the plaza (dubbed the pylon balance beam). The pylon balance beam is post-tensioned to the pier to complete the load transfer. The pylon balance stays provide an additional 15% offset to the transverse moment on the pylon base caused by the bridge deck.
The dimensions of the 57-metre high pylon cross section are 2.0 metres by 3.5 metres. The south face is curved with a 1.0-metre radius.
The design of the main walkway deck considered both flexural and torsional stiffness, as well as mass in order to obtain a system that behaves both dynamically and statically. The forces considered included the dead weight, pedestrian live loading of 5.0 kPa, as well as wind.
Permanent post-tensioning in the deck cross section was provided to ensure that at all stages of construction and normal service conditions the deck would be in compression (i.e. fully prestressed).
The 385-s.m., semi-circular centre plaza consists of a reinforced concrete slab that spans between tapered beams radiating out from the pier. The tapered beams are fixed at the pier and supported at the opposite end by the plaza cable stays. Should the stays fail, the structure has been designed to support itself as a cracked post-tensioned structure.
The sequencing of the deck and cable stay erection and installation was critical. Every stage of the construction was analyzed to ensure that no part of the pylon would exceed stress limits at any point. To reduce the stresses in the pylon and to eliminate the need for additional construction stays, the entire west span was erected on temporary falsework permitting balanced cantilever construction methods.
Wardrop designed a computer-based Structural Health Monitoring (SHM) system that incorporates sensors and a Data Acquisition system that is interactive and remotely monitored and evaluated. Engineering students at the University of Manitoba are able to participate in the monitoring through the ISIS Canada and NSERC programs.
The total project cost was $72.5 million, which included the vehicular and pedestrian bridges, the realignment of the approach roadways, underground works, and utilities (all of which were not in the original budget).
The pedestrian bridge opened on New Year’s Eve 2003. Mayor Glen Murray said, “Esplanade Riel is a wonderful example of art as public works that grows more exciting each day work progresses. I take pride in welcoming Winnipegers onto their new landmark structure.”
Name of project: Esplanade Riel, Provencher Bridges,Winnipeg
Award-winning firm: Wardrop Engineering, Winnipeg (C.D. Stewart, P.Eng., Robert van Ginkel, P.Eng., Rick Haldane-Wilsone, P.Eng., Dezi Yang, P.En., David Bowen, P.Eng., Bart Flisak, Gene Piasta, P.Eng., Arthur Liu, P.Eng., Craig Michaluk P.Eng., Emile Shehata, P.Eng.)
Owner: City of Winnipeg
Other key players: Rowan Williams Davies Irwin (wind tunnel testing), Dyregrov Consultants (geotechnical), Manitoba Hydro (hydrotechnical), Gaboury Prefontaine Perry Architects (bridge architecture), Hilderman Thomas Frank Cram (landscape), Speco Engineering (peer review)