Strand Jack Technology Outperforms Traditional Crane for Chicago Bridge Cantilever Lift York
Constructing the Cline Avenue Bridge while keeping the canal open to barge traffic, allowed heavy lift specialist Engineered Rigging to prove the flexibility of their Enerpac strand jack technology over a traditional crane approach to completing the span.
The new Cline Avenue Bridge is an elevated expressway in Northwest Indiana that connects the SR 912 to I-90, crossing over the Indiana Harbor and Ship Canal in East Chicago, Illinois. The bridge is 1.9 km long with a 96 m main span over the Indiana Harbor and Ship Canal, providing 30 m of vertical and 60 m of horizontal navigational clearance.
In the absence of traditional state funding to replace the Cline Avenue Bridge, innovation in its design and construction has been key. The privately-funded project has used low-maintenance concrete with an expected lifespan of over 100-years and a mix of traditional and new construction techniques. In total, the bridge comprises 29 cast-in-place concrete columns supporting 685 post-tensioned concrete single cell box girders segments which make up the bridge’s driving deck, with typical spans that vary between 52 m to 88 m. The piers range in height from 7.3 m to 26.2 m.
Assembly of the bridge was based on the balanced cantilever method with precast segments. Cantilevers were erected from the adjacent piers until they were within approximately 1.2 m of each other. A cast-in-place closure was inserted, after which continuity tendons were stressed across the joint to complete the span. In total, there are 28 cantilevers and 28 closure joint pours between cantilevers to complete the entire bridge. The bulk of the cantilever segment lifting and setting was completed using 2 separate large-capacity, ground-based, cranes. However, tackling the bridge span over the Ship Canal called for a different approach. Beyond the reach of ground-based cranes, some new thinking was required.
The bridge section over the Indiana Harbor and Ship Canal comprises 19 precast segments stretching 116 m column to column. The width of the canal is 40 m. Using a crane to lift the segments would have required floating the crane on a barge or using a floating crane to reach the midpoint of the canal span. Aside from the practical challenges of using a floating crane, this approach would have meant closing the canal to barge traffic for a number of weeks. Given the volume of maritime traffic that needs to use the canal, this was not a viable option.
“Cranes are great for lifting heavy objects, but their sheer size and cost often makes them impractical for some applications. Both factors came into play for the Cline Avenue Bridge project. Engineered Rigging was consulted to develop a practical alternative, and our expert engineering team was up for the challenge,” said Christopher Cox, president, Engineered Rigging.
Mr. Cox and his team had to take into account factors such as the weight and size of each segment and keeping any disruption to the busy canal to a minimum. The bridge segments measured 3 m high, 3 m deep and 9 m wide, and weighed 68 t. Engineered Rigging’s solution was to build the cantilever segmented bridge span using Enerpac strand jacks to lift the segments into position. While strand jacks are not the quickest lifting method, they provide massive lifting power in a small package. Moreover, they are secure, and their operation makes them essentially fail safe.
The strand jack lifting technique originates from the concrete post tensioning principle. A strand jack can be considered as a linear winch. In the strand jack, a bundle of steel cables or strands are guided through a hydraulic cylinder; above and below the cylinder are anchor systems with wedges that grip the strand bundle. A split flow pump is used to stroke the cylinders in and out while the grips are engaged in the anchors, a lifting or lowering movement is achieved. Over time, lifting systems maker, Enerpac, has refined the strand jack technique making it easier to deploy and manage with automated locking - unlocking operation, as well as enabling precision and synchronous lifting and lowering by a single operator.
Engineered Rigging developed a customized cantilever segmental bridge lift platform utilizing back span tie downs to counter the cantilever overhanging the bridge. Four 63.5 t strand jacks were used to lift the precast bridge segments into place across the waterway. Two beams extended from the platform with 2 strand jacks mounted on each beam. As each new segment was added the platform was moved forward using a combination of Enerpac launching cylinders and low-height skidding system.
The span construction involved placing the precast segment on a barge on the canal. Simultaneously the strand jack cables were lowered. The barge was moved under the cantilever lift system and each segment corner attached to a strand jack. Over the course of the next 2.5 hours the segment was lifted 40 m into position. During the final lifting stages, the strand jacks were also used to tilt and manipulate each segment as it was attached to the previous segment. Initially one segment was lifted and installed each day, although when canal traffic was light, up to 3 segments per day were added.
Engineered Rigging completed the bridge span in just 16 days. Project lead for Engineered Lifting, Mike Beres, points to the importance of synchronized lifting when using multiple strand jacks.
“Enerpac Strand jacks were integral to the safe and on-time completion of the project. They pack tremendous lifting capacity into a small footprint. Moreover, the system software can control up to 60 jack/pump combinations so the potential for synchronous lifting is quite scalable. The flexibility of the strand jack system has allowed Engineered Rigging to use this equipment on many other projects across multiple industries.”
The new Cline Avenue Bridge opened on December 23, 2020. The new bridge cost private operator United Bridge Partners more than US$100 million ($127 million) to build as a link to the casinos and steel mills along Lake Michigan. The 2-lane bridge is expected to carry 10,000 vehicles daily.
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