Strand Jack Versatility: Indoor, Outdoor, Underground
07/24/2024
Strand jacks are a powerful hydraulic heavy lifting solution that offer precise control. With capacities ranging from 15 tons all the way up to 1,450 tons in a single jack and boasting a small compact design, strand jacks are used to solve some of the world’s most complex lifting problems. The addition of computer control equates to a lifting system capable of controlling 60 individual jacks of varying sizes with massive total lift capacity. To fully appreciate the strand jacks’ capabilities, let’s explore some real-world applications.
Bridge Construction & Demolition
What is the most common lifting tool used in bridge construction? The most likely answer is a crane or hoist. However, there are times when a crane is not feasible due to site conditions, space constraints, cost of transport, or weather conditions. The compact size of a strand jack, combined with its ability to lift, lower or pull a load over long distances, makes it an ideal solution for bridge construction and demolition. Eight strand jacks were used to creatively support the pier foundation formwork during the construction of the 745’ long eastbound McClugage Bridge in Peoria, Illinois. The strand jacks were outdoors and under load for more than a year—a testament to their durability.
Strand jacks were subjected to more harsh conditions when used to dismantle the 90-year-old Wittpenn Bridge during a blustery New Jersey winter. The bridge’s deteriorating condition prevented the use of a grab and lower approach, and the close proximity of a railroad trestle added to the challenge. Counterweights were lowered using four inverted 200-ton strand jacks secured to the bridge’s main span lift towers as shown below.
Large-Scale Plant Maintenance
When Duke Energy’s Oconee Nuclear Station needed to replace two feed-water heaters, the job site presented tight clearances and equipment obstacles. The plant’s overhead crane didn’t meet the requirements for vertically extracting the old heaters which weighed 126,000 pounds and were 40’ long. For this challenge, strand jacks were used to create a temporary lifting device on top of the existing crane. The solution fulfilled the plant’s requirement for a single, failure-proof system that mitigated risk due to the unique hydromechanical design of a strand jack system.
Erecting & Dismantling Port Cranes
Cranes are a staple at ports around the globe, as they are used to load and unload containers from cargo ships. Strand jacks are a popular method for erecting and dismantling ship-to-shore (STS) container cranes. When the Virginia Port Authority needed to replace three STS container cranes, the challenge was how to dismantle the upper section of the crane which stood 150’ tall and weighed approximately 600 tons. The upper section included the main front boom, mast, backstay bracing, machinery house, trolley beams, hoist, trolley & spreader and operator cabin. Four 200-ton strand jacks were used to secure the load while it was cut free from the portal gantry legs. The strand jacks then safely lowered the entire upper section to ground level.
Applications Underground & Beyond
Strand jacks’ versatility extends beyond industrial plant, port and civil construction projects to include underground applications such as installing a mining shaft liner (see photo at top of newsletter) and mining machinery. Strand jacks were also NASA’s heavy lifting technology of choice to lower the 1.25 million pound crosshead onto Test Stand 4693 for the Artemis’ SLS rocket.
If you’re interested in leveraging the power of strand jacks, contact our heavy lifting experts to discuss your project needs.
How Does a Strand Jack Work?
Unlike traditional jacking systems, instead of pushing a load, the load is pulled up via a bundle of high-capacity steel wires called a strand. The strand is typically available in diameters of 0.62 inches (15.7 mm) or 0.71 inches (18 mm). The load capacity of the jack is determined by the number of strands which ranges from one to over 100.
The movement of the strand, and thereby the load, is powered by a group of cylinders (see image 1) including a hollow cylinder used to develop force and the upper and lower mini jacks which are integral to enabling incremental lifting, lowering or sliding.
Strand management is extremely important and may include an integrated strand guide (see image 2), which helps keep the strands in position when exiting the jack, and a recoiler which passively pays or takes up a strand bundle on system demand.
High reaction forces must be considered when using strand jacks regardless of strand jack orientation which could be horizontal or even upside down. When used in a vertical orientation for lifting or lowering, strand jacks are commonly on a support beam which may include the strand management system and hydraulic power unit in a sub assembly able to be flown in place by a support crane.
Engineered Rigging’s rental fleet includes the complete line of Enerpac Strand Jacks. All models feature Enerpac’s proprietary Smart Cylinder Control (SCC) System which provides precise control of synchronous lifting and lowering operations and allows fine adjustments to be made while lowering. The system provides clear feedback on distance travelled, stroke and load per point.
