N-Force Crane and Equipment, as the steel erector, in partnership with Spannovation as the erection engineer, recently completed a pivotal stage in constructing the new Athabasca River Bridge. A key achievement in this phase was the successful lift and placement of the 39-meter central span segment, stabilized with a stiffening truss, captured in the drone video captured by the site team. This accomplishment highlights the planning and expertise required to execute relatively complex operation safely.
Crane Placement and Lift
The central segment—a 39-meter-long steel plate girder with a depth of 3.5 meters and a weight of 45 tonnes—was reinforced with a top-flange stiffening truss that added another 8 tonnes, bringing the total lifted weight to 53 tonnes. A 400-tonne CC 2400 crane in super-lift configuration was used for these lifts. The crane is positioned on the east berm, approximately 7 meters in front of the pier centerline and about 11.5 meters away from the centerline of the exterior north girder line.
Center-Span Erection Procedure
The center-span erection procedure involves lifting each girder segment into position between the corresponding east and west cantilevered girder segments. To accommodate the center segment, the eastern girders are initially set about 50 mm east of their final position. During the lift, the crane carefully lowers and holds the center segment between the designated east and west splice points. The crew first aligns the segment at the west splice (seen in the video below), where they install the minimum required bolts.
After splicing on the west side, the east girder line is shifted 50 mm westward, closing the gap between the 17-meter cantilever on the east side and the central segment. During this process, cross-frames and diaphragm bolts remain loose, allowing each girder line to move independently. Once aligned, the splice on the east side is bolted into place. After placing and splicing the second girder segment using this procedure, and installing the minimum bracing to the first girder segment, the stiffening trusses are removed.
The remaining two 39-meter segments will be lifted using the same procedure in subsequent stages. The stiffening truss will be employed to ensure stability until each segment is securely braced to the previously erected segment.
Effectiveness of the Stiffening Truss
The stiffening truss played a crucial role in ensuring stability during lifting, countering the risk of lateral-torsional buckling (LTB). Without the truss, the unsupported girder length of about 43 meters, would have had a demand-to-capacity (D/C) ratio of 1.21, posing a risk of instability upon setting.
By adding the 2.7-meter-wide truss, the girder’s bending capacity was greatly enhanced. The truss increased the girder’s moment of inertia about the weak axis by approximately 5.82 times and about the strong axis by 1.11 times, resulting in a marked improvement in its resistance to lateral-torsional buckling. With the truss in place, the D/C ratio was safely reduced to 0.2, ensuring structural stability throughout the lifting and placement process.
The successful lift of the center-span segment marks a significant step forward in the Athabasca River Bridge project. The collaboration between N-Force and Spannovation has helped move the project closer to completion, demonstrating careful planning and a strong focus on safety. As work progresses, the team remains committed to building a durable and important piece of Alberta's infrastructure.
Owner: Alberta Transportation
Designer: COWI
General Contractor: Alberco Construction Ltd
Fabricator: Central Welding & Ironworks
Erector: N-Force Crane & Equipment Ltd.
Construction Engineer: Spannovation Consulting
Comments