Videos: Wired for strength: Strand jacks made simple
21 May 2018
By Piet Nooren (Executive VP. Technical Director at Mammoet USA)
Strand jacks lift, slide, support and transfer large and heavy loads along a straight line. Strong, yet compact, they are ideal for situations where there is limited space for other heavy lifting equipment.
How strand jacks work
Strand jacks use multiple strand wires, a type of braided wire with more flexibility than solid steel. The jacks are hollow inside and have two sets of wedges, one set at the top and one at the bottom. The strands are alternately gripped and released by these wedges. The system lifts by following a sequence of pulling and gripping the set of wires attached to the load:
1A. The strand is gripped by the wedges at the top of the cylinder.
1B. The strand is pulled upwards by the hydraulic cylinder while the lower wedges are loose.
2A. The strand is then gripped by the lower wedges and kept in place.
2B. The cylinder moves back down while the top wedges are released.
3. The strand is gripped once more at the top of the cylinder and then released by the wedges at the bottom and so the cycle of gripping and releasing by each set of wedges is continued until the load is in place.
After every stroke the lift stops as the strand jack takes grip again so, unlike hoisting or winching, it is not a continuous lifting motion.
Strand movement with load going down
Lowering a load
Going down with a load is a little more complicated because the strands need to be pulled up to release the bottom wedges before the cylinder can travel down.
Like water from the well
When you pull a bucket of water out of a well you use your arm and hands to pull it up. The hand works like the wedge clamping on the rope, the arm works like the cylinder making the stroke.
The strand jack has been used by the heavy lift industry for over 50 years. They pull or lift a load and generally require less equipment to be mobilized than for a crane lift.
Mammoet’s fleet of over 200 strand jacks range in individual capacity from 15 to 900 tons. If you think about lifting a bucket of water at arms length, rather than if you stand directly over the bucket, you understand that when you lift things from the side, or at an angle, the higher the load is lifted, the more strength is required.
Unlike cranes, which experience this because of the angle at which their booms are placed, strand jacks exert their force in a direct line, above the load. This means they can continually raise the same amount of weight without losing capacity.
With their small footprint they are suitable for confined spaces. Using multiple strand jacks together enables more concentrated lifting capacity. When projects require many strand jacks to be operated simultaneously and in synchronicity they are coordinated and controlled by computers.
How strand jacks are used
Strand jacks are used in different configurations for a wide range of operations.
Learn more about Mammoet’s strand jack system: https://www.mammoet.com/equipment/special-equipment/strand-jack-system/strand-jacks/
Watch the videos below:
Operating Principle of a Strand Jack
Mammoet’s Strand Jacks offer faster and more efficient routes for transporting heavy objects horizontally or vertically, even in situations where the amount of available space is limited.
They can be used on gantries, but they can also be installed on clients’ structures. The capacity of Mammoet’s strand jacks ranges between 15 to 900 metric tons each, allowing clients to select the ideal type and capacity to meet the specific needs of each project; their lifting power can be further increased by using multiple jacks for one lift.
This video clip shows the different parts of a strand jack, and demonstrates how each of these parts work.