In the past, most bridges were functional structures and not works of art. Aesthetics and architecture are becoming more and more important in all municipal structures. When the call came to replace the 90-year old Provencher Bridge, the city council of Winnipeg decided to create a landmark structure and use it as the symbol of their commitment to the transformation of the downtown Winnipeg core. Located near the junction of the Red and Assiniboine Rivers, the new bridges provide a crossing over the Red River and links to the Forks, a national historic site on the west, and St. Boniface, the city's vibrant French Quarter to the east.
The wining design had distinctive dual function bridges; a suspended pedestrian bridge and a four-lane vehicular bridge that branches off from a shared abutment on the east bank.
The vehicular bridge is designed primarily for vehicles and commuter cyclists. This bridge is a 250 m long five span, precast, post-tensioned, trapezoidal concrete girder structure.
The pedestrian bridge was designed exclusively for pedestrians, cyclists, and recreational users. This bridge is a cable-stayed structure. A 40 m high pylon supports a 5 m wide concrete deck spanning 106 m east and 86 m west. A large plaza for commercial activities was located at the pylon; quite unique for a North American bridge.
To avoid traffic and business disruptions both bridges were built in phases. The vehicular bridge was begun in 2001 and completed in October 2003.
Project Sequence
Replacement of existing Provencher Bridge was accomplished with little traffic disruption. Traffic was narrowed on the existing bridge for the construction of the new bridge. Next, traffic was transferred to the new bridge and the old bridge was demolished. Finally, the aesthetics on new bridge was completed.
Precast Solution
The use of precast/prestressed concrete in bridge construction continues to increase throughout Canada. The durability, cost effectiveness and low maintenance benefits have made precast concrete the dominant structural material for short and medium span bridges. Long span bridges benefit from the inherent qualities of precast concrete by combining post-tensioning with girder splicing. The Provencher Bridge was designed using trapezoidal precast box girders, pier girders and plaza girders. Individual girders range in length form 25 m to 29 m for a total length of approximately 245 m.
Girder Production
Two concrete girder molds were used; one was adjustable for the pier and plaza girders and one was non-adjustable for the drop-in and abutment girders. One girder was produced each day in each form. Steel reinforcing cages were preassembled in a special jig at the side of the plant. The reinforcing cage was fastened in the form and the prestressing strands were tensioned. Pier girders with projecting bottom haunches were prestressed and post-tensioned for handling, transportation and erection. The post-tensioning was removed once the girders were in place.
A steel "tub" was placed inside the concrete girder to form the interior surface. Self compacting concrete was poured from one side and allowed to flow to the top of the other side. The self-leveling mix required no vibration. There was no segregation of the mix during placement of the concrete.
Each girder was steam cured for 12 hours with the steam applied 4 hours after casting. Girders were stripped the following day and remained in the plant for 3 days.
Erection and Delivery
To minimize traffic disruption delivery occurred at 4:00 AM with a police escort. Girders were erected by a 440 ton crane, the largest crane in Canada. Girder weights ranged from 95 tons to 105 tons.
The first move-in began at the west end. Four sets of haunched pier girder segments, 5 girders wide, were erected first and tied integrally into the supporting piers adjacent to the river. Five sets of drop-in segments, also 5 girders wide, were installed between the haunched girders. Joints between the ends of the girders were concreted and the bridge segments were post tensioned together.
Shallow section prestressed abutment girders, 2,250 mm deep, were installed at the vehicular bridge approach. Deep section prestressed plaza girders, 3,000 mm deep, were installed at the footbridge approach.
A total of 49 girders were fabricated, with the complex process beginning in late 2001 and wrapping up with a completed bridge structure in 2003.The total project costs $72.5 million, which included both the vehicular and pedestrian bridges, approach roadways, underground works and utilities.
Applied Research
The 200-m long pedestrian bridge has a concrete deck, steel stay-cables and a 60-m post-tensioned concrete pylon encased in a steel jacket. The 5-m wide deck was built using segmental construction with post-tensioned concrete. The City of Winnipeg has committed over $200,000 towards a structural health monitoring (SHM) plan to assess the in-service performance of the innovative bridge design and providing a decision-making program that will optimize long-term maintenance costs.
The monitoring program will measure movement, traffic flow, wind speed and direction, stay cable forces and strains, ambient temperature, temperature gradient, and 3-D acceleration of the deck and pylon. Intelligent Sensing for Innovative Structures (ISIS Canada) will supplement the City's plan with the installation of 20 fibre optic sensors, lead wires, and a fibre Bragg grating strain indicator, and will play a key role in implementing the decision-making software.
ISIS Canada president, Dr. Aftab Mufti, is proud a high-tech product that could eventually spread around the globe was developed in Winnipeg. As an added bonus, engineering students at the University of Manitoba were able to participate in the project through ISIS Canada and the Natural Sciences Engineering Research Council of Canada (NSERC) programs.
The Paired Bridges have strengthened the connection between The Forks and the St. Boniface French Quarter, becoming a symbolic gateway between two of Winnipeg's most historically significant communities.
Credits:
Client/Owner: City of Winnipeg
Prime Consultant: Wardrop Engineering, Winnipeg
Architects: Gaboury Préfontaine Perry Architects
Other Consultants:
Rowan Williams Davies & Irwin (wind tunnel testing)
JMBT Structures Research
ISIS Canada (monitoring)
Manitoba Hydro (hydraulics)
Dyregov Consultants (geotechnical)
Hilderman Thomas Frank Cram (planning/landscaping)
Speco Engineering (peer review)
Contractor: M.D. Steele Construction
Precaster: Lafarge Canada (Precast Division)
