The wide bottom NU girder flange provided substantial lateral restraint to wind loads during both shipping and erection. Permanent galvanized steel angles, spaced at 7.5 m c/c and used for the intermediate diaphragms, facilitated girder stabilization during erection.

Concrete diaphragms are cast at the piers and abutments for structural continuity and end waterproofing. Multi-cell expansion joints, one at each end of the structures, are installed on all the floodway highway bridges.

Structural Health Monitoring
The Structural Health Monitoring (SHM) system was designed to be incorporated into the replacement bridge over the floodway on the Trans Canada Highway. The SHM system will be used to monitor the dynamic behaviour of the bridge by the ISIS Canada Research Network: www.isiscanada.com

The remote monitoring program will provide basic information on the structural behaviour of the bridge. The system will be tested using a control vehicle to obtain the initial responses and to calibrate the system.

Substructure Design
All six highway bridge sites (ten bridges in total) were built using reinforced concrete abutments and reinforced concrete hammer head piers.

At the upstream, the soil stratigraphy at the bridge sites consists of a top layer of high plastic lacustrine clay, followed by a layer of soft buff peebly till underlain by a layer of dense till with limestone fragments. This soil profile permits the use of hexagonal, 406 mm diameter, precast stressed concrete piles that bear on the dense till.

At the downstream, in some cases, the dense till is almost at the bottom of the floodway channel. Spread footings or short steel piles were used at these bridge sites. Prestressed precast concrete piles will be used at the abutments.

Hydraulic Forces
The 1 in 700 year’s discharge is 3,960 cubic m/s (140,000 cfs). This translates into a velocity of between 1.5 to 2.1 m/s at the various bridge sites. The structures are designed to accommodate maximum ice floes of 15 m diameter by 0.6 m thick. All bridges have a minimum clearance of 300 mm to the underside of the girders at high water level.

RAILWAY BRIDGES
The six existing railway bridges each consist of 11 spans, range in length from 245 to 275 m, and are operated by four different authorities:

•2 – CNR
•2 – CPR
•1 – Central Manitoba Railway (CEMR)
•1 – Greater Winnipeg Water District (GWWD)

Four of the existing bridges use steel deck plate girders, one of the CPR bridges uses ballasted steel through plate girders with a concrete deck, and the GWWD bridge uses ballasted prestressed concrete I-girders with a concrete deck. All of the bridges are single track, except one CPR bridge has double tracks.

The project involves modifying five of the existing bridges and replacing one bridge. All, but one, of the railway bridges reuse the existing substructures, retrofitted to accommodate new superstructures. The deck plate girder bridges will be replaced with ballasted steel through plate girder superstructures to raise the underside with minimal adjustments to track profiles. Each of the new and retrofitted railway bridges has a unique design.

The new girders for the CEMR Bridge will be fabricated first and used in sequence as the superstructure for detours at three other bridge sites.

Railway operation requirements for the four bridges used by the two national railway companies, all located on high-speed main-line track, required keeping the existing tangent alignments, maintaining traffic without any significant delays or interruptions during the work, limiting longitudinal gradients and increasing the level of live loading by up to 50%.

The remaining two railways are low-speed low-volume short-line operations that service the City of Winnipeg’s main public water supply and a paper mill. Negotiations with the two short line operators resulted in agreements to shut down their tracks for a few months to complete the modifications.

Detour Design
A single temporary detour design was developed to be compatible with the existing channel cross-section at the three sites that require a detour structure. The spans for one of the short-line bridges were designed for main-line live loading so that they could be used in the detour bridges. An innovative construction staging plan was developed that relocates the detour bridge along the project one site at a time until the spans become free for installation on the CEMR bridge at the end of the project.

Temporary Precast Rail Piers
The temporary piers for the 3 detour rail bridges used match-cast precast segments, varying from 3 to 8 segments high. Typical segments were 7750 mm long, 2500 mm wide and 1120 mm high, each containing 3 voids to reduce the weight. Cap pieces were solid precast, 500 mm high, to receive the bridge bearings and superstructure. Typical segments weighed 27.2 t. Base units were accurately located 40 mm above the pile cap, using levelling cleats, before the base joint was grouted. A bond breaker was applied to the underside of the base unit to accommodate future removal. Vertical sleeves were cast through all the segments for temporary post-tensioning bars that stressed the segments together.

The Phase 1 construction sequence was:

•Precast the pier segments using match casting
•Place the pile caps
•Erect the precast segmental pier segments
•Stress the pier segments to the pile cap
•Erect the steel deck plate girders
•Divert the rail traffic onto the temporary bridge

The Phase 2 construction sequence was:

•Disassemble the steel deck plate girders
•Destress the pier segments
•Disassemble the segmental pier segments
•Move the girders and pier segments to the next site
•Repeat the Phase 1 construction sequence

The budget value for the railway modifications and upgrades will be $160 million over the next 4 years.

Conclusion
The predesign for the Floodway Expansion Project followed a three phase iterative design process which considered channel deepening, channel widening, raising bridges, and lengthening bridges. An optimum design was achieved, enabling the initial projected project budget to be maintained.

At this time, two highway bridge site crossings and one railway crossing are under construction. In the fall of 2006 and during the winter 2007, one more highway crossing and two more railway crossings will begin construction.

The final design and construction began in 2005. Dillon Consulting Limited is the lead consultant in association with EarthTech, ND LEA, UMA, and Wardrop.

The overall Floodway Expansion Project, including the bridges, is scheduled for completion in 2009. Total project cost is estimated to be $800 million.