Strand jacks 101: the basics behind big lifts

The hydraulic strand jack is a highly specialized yet adaptable tool within the heavy lifting industry, capable of being configured for a wide range of loads, geometric lift points and operational requirements.

FIGURE 1: Strand jacks are a driving force for innovation, offering new applications for industries around the globe.

Despite their compact footprint, hydraulic strand jacks – when integrated with high-strength steel strands, hydraulic power packs, lifting anchors and a computerized control system – offer capabilities that far exceed those of conventional lifting equipment.

A key advantage is a strand jack’s ability to perform synchronous lifting, where multiple jacks are operated together to raise heavy, complex and even odd-shaped loads without causing racking, twisting or overloading. Strand jacks are increasingly being explored for a wide range of material handling projects in contemporary heavy lifting operations and below, we will discuss their history, purpose, functionality and the various project applications used today.

The strand jack was developed in the late 1950s or early 1960s, during a period of rapid global growth in infrastructure, oil and gas production and power generation to support expanding post-war economies. The demand for larger power plants, high-output oil rigs, gas facilities and bigger bridges helped to create a need for lifting solutions capable of handling much greater loads, often in confined or restricted environments. These requirements frequently exceeded the scale and reach of the cranes available at the time, driving the innovation of more powerful and compact lifting technologies like the strand jack.

Origins explained

The concept was derived from prestressing techniques in concrete construction, where steel strands are tensioned under load to strengthen structures. Engineers and construction companies realized that by mechanically gripping and using hydraulic jacks to incrementally “walk” up or down the strands, it was possible to move or support extremely heavy loads from a vertical, horizontal or even inverted orientation. Over time, the strand jack system has evolved into a very efficient type of linear winch which handles greater weights, delivers loads at higher elevations, creates precision movement, offers multi-point synchronization and provides a mechanically fail-safe lifting operation.

EXAMPLE 1: Crofton & RLT Engineering utilize strand jacks for dismantling the STS crane boom during demolition. PHOTO: CROFTON & RLT ENGINEERING

During my research, I reviewed the website for Mammoet, one of the world’s premiere heavy-lifting companies, which features a resource page titled “Piet Explains Strand Jacks.” Piet Nooren, having spent his career on heavy lift and transport projects all over the world, provides a simple, yet precise description of how a strand jack works. To paraphrase his explanation online, “Strand jacks operate using multiple-strand wires, a type of braided wire that offers greater flexibility than solid steel. The strands run through an engineered center-hole jack which is equipped with two sets of wedges – one at the top and one at the bottom. During operation, these wedges alternately grip and release the strands in a controlled sequence to lift the load. First, the upper wedges grip the strands, allowing the hydraulic cylinder to pull the strands and the load upward while the lower wedges remain disengaged. Once the desired stroke is completed, the lower wedges engage to hold the load in place, and the cylinder retracts as the upper wedges release. The cycle repeats, with the upper wedges gripping again and the lower wedges releasing, allowing the system to incrementally lift the load with precise control.” (See Figure 1, Strand Jack Operation).

He continues that, “Using multiple-strand jacks together enables a more concentrated lifting capacity. When projects require many strand jacks to be operated simultaneously and in synchronicity, they are coordinated and controlled by computers.”

Nooren is referring to the computer system and lift program that enables precise control during lifting operations. It also allows a single operator to monitor and manage up to 60 strand jacks operating either independently or in unison.

Strand specs

Another important aspect of the strand jack is the specification of the strands themselves. The most commonly used strand is a 7-wire, 0.62-inch (15.7 mm) diameter prestressed, wound, uncoated steel wire, typically rated for a breaking strength of 62,800 lbf (279 kN). (A .71-inch/18 mm diameter strand is also available with a breaking strength of 79,400 lbf (353 kN.)

The overall lifting capacity of a strand jack – and ultimately of the complete system – is determined by the size of the strand, the number of strands utilized and the size/capacity of the hydraulic cylinder. This modularity allows systems to be customized to meet specific project lifting requirements. For example, one strand jack might offer a 79-ton (70 metric ton) capacity using seven total 0.62-inch diameter strands, while another model may achieve a 562-ton (500 metric ton) capacity using forty-eight total strands of the same diameter.

EXAMPLE 2: Mammoet uses a strand jack system and heavy-lift frame straddling the shaft to provide controlled and safe lifting/lowering operations for TBM components. Photo: Mammoet

The jack housing, frame and associated hydraulic components are all engineered to support the specific loading requirements and to maintain proper load transfer within the compact equipment footprint. In North America, the commercial sales market for strand jack systems is relatively specialized, with only a few manufacturers – such as Enerpac, Dorman Long Technology and VSL –dominating the field through equipment sales, project support and service offerings. With that being said, there are many of the major North American heavy lift service providers which also manufacture in-house systems for specific project applications including Fagioli, Sarens, Barnhart, Mammoet and others.

When we look at the application uses over the past two to three decades, we still see the hydraulic strand jack systems in service today lifting extremely heavy loads in situations where traditional cranes were impractical. They continue to successfully complete project tasks such as lifting precast segments for bridge construction, setting reactors, steam turbines and generators at power plants, aligning and lifting super-heavy ship modules, erecting reactor vessels in refineries and sliding topside jackets on barges just to name a few.

EXAMPLE 3: Barnhart recovers collapsed bridge spans partially submerged using strand jacks and a modular lift tower all mounted on modular barges for the retrieval and removal operation. Photo: Barnhart Crane & Rigging

Emerging applications

However, more recently and into the future, strand jacks appear to be reshaping the possibilities in heavy lifting, enabling a wide range of growing market segments to pursue unique engineering solutions and new project opportunities with their use.These project applications span from the synchronized dismantling of STS crane booms for demolition (Example 1), lifting prefabricated high-rise floors for a “top-down” construction process, providing a controlled and safe lowering for bridge falsework, lifting and lowering of TBM (tunnel boring machine) components in shafts (Example 2), launching of completed bridge spans, lifting of prefabricated stadium and commercial building roof systems and even recovering bridge spans from a lake (Example 3).

Ultimately, the use of strand jacks is now so advanced that loads of 10,000-plus tons can be lifted with millimeter precision – something that no crane or conventional jacking system could dream of handling alone. Strand jack systems consistently address diverse challenges in the heavy lifting field, ranging from variations in project component size and capacity to meeting lifting precision and safety requirements. They remain a driving force for innovation, offering new applications for industries across the globe.

THE AUTHOR

Eddy Kitchen, owner and founder of Kitchen’s Crane and Equipment (est. 2007), has worked in the crane, rigging and transport industries for 30-plus years, offering heavy lift and transport equipment sales and rental solutions.