Strand jack 3986309 209965108 2008-05-03T20:12:25Z 81.154.186.158 {{Orphan|date=November 2006}} '''Strand jacks''' (also known as '''strandjacks''') are [[jack (device)|jacks]] used to lift very heavy loads for construction and engineering purposes. Capable of lifting loads of over 400 [[ton]]s, strand jacks were invented in the 1970s.{{Fact|date=March 2008}} The strandjack lifting technique originates from the concrete post tensioning principle. A strandjack can be compared to a single-part winch. In a strandjack a bundle of steel cables is guided through a [[hydraulic cylinder]]. Above and below the cylinder is an anchor system with a number of grips. Those grips can clamp the cable bundle. By stroking the cylinder in and out while the grips are engaged in the anchors a lifting or lowering movement is achieved. The motion of the cylinders is driven by hydraulic power packs. They can be electric or diesel powered. A sophisticated software program synchronizes the motion of the strandjacks and adjusts the motion to the loads per lifting point. This program can operate and control dozens of strand jacks simultaneously. During operation all loads and anchor positions are displayed on the screen of the control unit. '''Strand jacking''' is a construction process whereby large construction elements (such as concrete slabs and steelwork) are lifted into position with computer-controlled hydraulic jacks. Because the multiple jacks can be moved in unison and with great precision, heavy structures can be assembled at ground level and then lifted into position, rather than having to be built in the air. Traditional cranes and other lifting methods cannot provide this level of precision. In December, 2005, Bigge, a [[United States|U.S.]] supplier of strand jacking equipment, announced plans to lift the first 2,000 ton [[transition span]] for the newly-renovated [[Oakland Bay Bridge]] into place using four strand jacks mounted on steel girders above the bridge deck. Each of the four jacks had a [[lifting capacity]] of 365 [[ton]]s, and could maintain a precision of 1/32 of an [[inch]]. Other structural applications have been the raising of the 316 metre span, roof-supporting arch over Wembley Stadium, London, UK and the raising of the London Eye observation wheel from the horizontal to the vertical position. Strand jacks have also been used in other lifting applications, such as marine salvage. For example : salvage of the submarine Kursk. ==External links== * [http://www.wbequipment.com/strandjacks-bigpic.htm Diagram of a strand jack] {{industry-stub}}