Strand jacking

Strand jacks are hydraulic jacks used to lift very heavy loads for construction and engineering purposes 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. Strand jacks can be used horizontally for pulling objects and structures and widely used in the oil and gas industry for skidded loadouts.

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 by 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.