Bridge makeover

Edmonton's busiest bridge is widened, updated

The 315 m long Quesnell Bridge on Whitemud Drive has the highest traffic flow of any bridge in Edmonton. It carries approximately 120,000 vehicles per day, which means at least 10,000 vehicles per hour during peak morning and afternoon periods.

Edmonton residents who commute to the city's west end via the Whitemud received a Christmas gift of sorts last winter when the northbound ramp that leads on to the drive where it crosses the North Saskatchewan River on the Quesnell was re-opened for traffic on Dec. 23.

The westbound lane of Fox Drive, which provides access to the ramp, had been closed except for transit buses for much of 2009, as part of the city's $161-million Quesnell and Whitemud Drive widening and rehabilitation project. Traffic had been detoured to a point about 1 km south of the bridge since the ramp closed for construction the previous April.

Since the start of planning for the three-year project, which is scheduled for completion in November, maintaining reasonable traffic flow, while allowing for slower speeds, has been a priority.

"The challenge was a traffic management plan for the city's busiest bridge," says Byron Nicholson, roadways construction director with the City of Edmonton's capital construction department.

"During construction, we've been able to maintain five out of six original lanes open for traffic, albeit narrower lanes and with traffic moving at a slower pace."

The original price tag for the project had been pegged at $181 million, but dropped in the wake of the sharp economic downturn, Nicholson says.

To help monitor and manage traffic flows, the city deployed an extensive network of cameras and 64 digital messaging signs along and around the construction area. The messaging signs are located along key corridors and provide real-time traffic updates to allow motorists the opportunity to find alternate routes when necessary.

The Quesnell Bridge opened for traffic in 1968. This project marks its first major rehabilitation. It should extend the life of the bridge by up to 50 years.

Originally, the bridge had three lanes (including ramp lanes) in each direction, but without shoulders, while the newly widened bridge will have four lanes (including ramp lanes) each way, plus shoulders. Adjacent sections of Whitemud Drive, including the Fox Drive overpass just south of the bridge, totalling about 3 km, are being widened from two to three lanes each way.

The old bridge deck is being removed and replaced. Also, says Nicholson, "The plan was to widen the bridge without more pier extensions into the water. Instead, we've built onto the existing concrete piers new extensions to support the widened road."

Construction by ConCreate USL Ltd. on the bridge and overpass components of the project also involved replacement and widening of the Fox Drive overpass structure, and included strengthening of existing girders and the erection of some new ones.

The original bridge had 10 rows of pier-to-pier girders. To accommodate the widening, two additional rows of girders were added, bringing the total to 14 rows.

"Re-enforcing was done on the existing girders, via a fibre wrap. It's a new technology and involves encasing the existing girders with a kind of high-tech fibreglass," says Derek Martin, VP of ConCreate USL and the senior project manager for the project. He says the company typically does 70 to 80 bridge projects across Canada annually.

With much of the work being done at considerable heights above either water or existing roadway with traffic on it, extensive scaffolding was required. Peri Scaffold Services, a division of Peri Formwork Systems Inc., supplied scaffolding services. The Peri UP Rosett modular scaffold system formed the basis of most of the scaffolding. Much of the scaffolding was below the bridge deck level and the complex scaffolding network also incorporated and provided support for Peri LGS, a lattice girder system for large spans.

The suspended scaffold structure provided access points and work platforms for around the pier heads and other areas below the bridge superstructure.

With space on the bridge at a premium, there were no spare lanes for staging, "so we had to use the sidewalk for the staging area. It could be a challenge with the height and the water below," says Dean Dancey, western regional manager for Peri.

"The movement of water below can be disorienting, even for those used to working on scaffolding at heights."

A section of the bridge also spans a roadway to a nearby park, which remained open throughout construction, so measures were taken to ensure that nothing fell on traffic moving below - or into the river.

"The working platform had to be closed in so no debris from demolition was falling onto the road or in the river," Dancey says.

Scaffold towers composed of standard Peri UP components support the LGS structure, which is constructed to provide stable load-bearing units that span the entire width of the roadway. The units provide safe work platforms and secure access points to the underside of the bridge.

The LGS work platforms below the bridge superstructure were designed as mobile units that could move along aluminum rails. "This means that the truss girders can be simply and easily moved by hand," Dancey says.

There were two main reasons for this type of support system, he says.

"Firstly, the working area, as well as the crane capacity, available for erecting the LGS structure was limited," he says. "As a result, the structure was pre-assembled on the bridge in small units, and then lowered by crane onto the supporting towers and connected. Secondly, only half the bridge was refurbished at a time. For the remaining half, additional scaffold towers are erected along the lanes, and the LGS system can be simply moved into place under the second half of the bridge."

Given the stakes, cost and nature of the project, it is perhaps just as well that, as Dancey says, "we have system design capabilities that are well targeted for complexities."

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