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  • Writer's pictureRaj Singh

CASE STUDY: Tandem Lift of the Mount Hunter Creek Bridge Girder Pairs

In 2009, the Mount Hunter Creek Bridge was constructed to replace an old, non-composite two-lane structure on the Trans-Canada Highway, near the Kicking Horse Canyon Route in the Rocky Mountains. This new four-lane bridge, with its six steel plate girders and composite cast-in-place concrete deck, brought significant improvements to the region. Given the mountainous geography and the bridge's single span design, an innovative approach was adopted using a tandem lift of the girder pair by two 300T cranes followed by a transverse launch was implemented to move the girders to their final positions. This article focuses on the tandem lifts that needed to be accomplished within three consecutive night closures of the highway.

Tandem Lift in Execution using an DEMAG CC1500 & LTM1250. The terrain has dramatic slopes preventing access along the span.
Rendering of site, truss bridge along the previous Hwy 1 alignment & tandem lift scheme for lifting the girder pair

Transport of Assembled Girder Pairs

3.5m deep steel plate girder segments, which were fabricated in Armstrong, British Columbia, were trucked 300 kilometers to the construction site on their sides due to height restrictions. Each girder was assembled using three segments connected at two field splices. The girders were connected with cross frames to create a pair of girders, weighing about 220 tons. Once the girder pairs were assembled, they were placed on trailer beds supported by six sets of independent dollies and the fifth wheel of a semi-tractor. This set-up allowed the girder pair to be transported immediately following the road closure. Transporting the pair involved navigating an 80-meter span with multiple sets of dollies, and due to the sag in the vertical alignment of the Highway, there were instances when inner sets of dollies temporarily lifted off the asphalt. With careful maneuvering using the steering mechanism on the front set of dollies guided the girder pair into its tandem lift positions.

Tandem Lift Assembled Pair on Trailer & Steering Dollies
Tandem lift of assembled girder pair onto trailer & steering dollies

Crane Placements for Tandem Lifts

The strategic placement of the cranes was vital for the tandem lift during the project. The new bridge was situated alongside the existing one, in an off-line alignment, to maintain traffic flow during construction. However, the new and old structures weren't parallel, resulting in a significant offset between them at the west abutment. The two 300-ton cranes, an all-terrain hydraulic LTM1250 and a crawler crane DEMAG CC1500, had to be precisely positioned at the east and west abutments respectively to perform the lift within their capacities.

The all-terrain crane was placed so that two of its outriggers were positioned above the concrete retaining walls of the north face of the existing bridge's abutment, while its other two outriggers extended beyond the south face of the abutment. Pads for these two outriggers were placed on custom fabricated steel bearing plates, anchored into the abutment, and supported with HSS struts and steel pipe pile.

Due to the offset between the two bridges at the west abutment, the conventional crawler crane would have lacked the necessary capacity to place the girders onto the new abutment if it had been positioned within the existing Highway's corridor. To remain within its capacity, this crane was positioned between the alignments of the new and existing bridge. Given the narrow shoulder and the sudden drop of a steep embankment, a temporary work bridge was required to support one of the conventional crane's tracks, while the other track was supported by crane mats placed on the Highway's shoulder. The construction of these temporary works was completed in the weeks leading up to the scheduled night closures.

Execution of Tandem Lifts

The Highway was closed to allow the positioning of an all-terrain crane at the east abutment. However, the crane couldn't be moved with full counterweight. Once in position and correctly set up, the crew leveled the crane and used a smaller 65T rough terrain crane to rig and lift the additional counterweight. Concurrently, the girder pair was transported from the staging area to the lift position, a process that took approximately two and a half hours.

At the east abutment location, the crawler needed to be positioned with one track on the Highway shoulder and the other on a temporary work bridge. Unlike the all-terrain crane, the crawler could be moved with full counterweight on a level travel path. However, the transition from the highway to the lift position was uneven, requiring the full counterweight to be installed when the crane was in its correct lifting position.

Once both cranes were set up and the girders were in place, the lifting radii at each pick and drop point were checked. This was accomplished by moving the cranes' main lines to each point, allowing the operator to read the radii from the crane console. Each radius was further verified manually using a chain. The crawler crane lifted the girders 6.5m from the end. The first lift set the end of the girders directly onto sliders positioned in the launch rail at the east abutment, while the west end of the girders was set onto an intermediate position on a temporary bent.

Tandem lift in progress  - LTM1250 mobile (left) and DEMAG CC1500 crawler (right)
Tandem lift in progress - LTM1250 mobile (left) and DEMAG CC1500 crawler (right)

Thereafter, the crawler crane's pick point was adjusted to reduce the lifting radius and enable the girders to be picked up and lowered onto the sliders in the launch rails at the west abutment. After the second lift, the cranes were de-mobilized and the Highway reopened. The lateral launch of the first pair of girders was completed later that afternoon without requiring a Highway closure. The process was repeated for the other two girder pairs in subsequent night closures, which took less time due to the learning curve.

Ledcor served as the general contractor, with Surespan Construction as the steel erector, and Infinity Engineering as the erection engineer. The author contributed to this project as the Lead Engineer while employed at Infinity Engineering.

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