Strand jacking is a construction process whereby large pre-fabricated building sections are carefully lifted and precisely placed. Strand jacks are jacks used to lift very heavy (20,000 tons or more with multiple jacks) loads for construction and engineering purposes.

The Octamec Group has pioneered the use of the Hydraulic Strand Jack technology in India when it constructed the largest span space frame aircraft hangar for Air India in Mumbai. Ever since then, Octamec has successfully used the Strand Jack technology for many of its projects including the new terminal building at Chandigarh airport, the aircraft hangars at Shamshabad airport for Air India, Mas GMR among others.

Strand jack technology can not only raise or lower heavy loads but can do so within tight operational tolerances and over long distances. The use of synchronised heavy lifting with strand jacks is now becoming a standard tool for construction of projects. Strand jacks give the engineer more flexibility in the design of projects which otherwise may not have been possible. Designs that were previously discounted for constructability reasons can now be reconsidered as viable options.

Strand jacks were invented in Europe in the 1970s as a development of post tensioning systems and are now used all over the world to erect bridges, offshore structures, refineries, power stations, major buildings and other structures where the use of conventional cranes is either uneconomic or impractical.

A strand jack is a hollow hydraulic cylinder with a set of steel cables (the "strands" in the name) passing through the open centre, each one passing through two clamps - one mounted to either end of the cylinder. The jack operates in the manner of a caterpillar's walk: climbing (or descending) along the strands by releasing the clamp at one end, expanding the cylinder, clamping there, releasing the trailing end, contracting, and clamping the trailing end before starting over again. The real significance of this device lies in the facility for precision control. The expansion/contraction can be done at any speed, and paused at any location.

Strand jacks can be used horizontally for pulling objects and structures and widely used in the oil and gas industry for skidded loadouts, speeds of up to 40m/hr and Oil rigs of 38,000T have been moved in this way from the place of construction on to a barge.

As strands can only act in tension, a strand jack cannot push a load and is primarily used as a lifting device in the vertical direction. However, a strand jack can be used in any direction as long as tension is maintained in the strands.

The high tensile strands used in strand jacks are of the same solid wire used in pre and post tensioned concrete. These strands are often run through an additional manufacturing process to reduce their diameter further by flattening/rounding slightly the outer wires to give the strand more circumferential contact area (Figure 1). The reduction of diameter means more strands can be utilised within a given area although the sectional areas are the same. Additionally the increased circumferential area allows more contact area with the collets and hence less wear.