The strand jacking system developed by Enerpac (A Division of Actuant Corp) was recently used to hoist and position 135-ton concrete girders at a bridge project above a deep gorge in Hawaii.
The Enerpac strand lift technology of a type already being deployed in Australia and New Zealand was put to use during the construction of the new Kealakaha Stream bridge, a part of Hawaii Route 19.
The strand lift system is capable of safely positioning huge loads to accuracies within fractions of a millimetre. Strand lifting is one of the heavy lifting solutions deployed in Australia by Enerpac Integrated Solutions for tasks ranging from bridge lifting to positioning of huge infrastructure.
Using PLC controlled-synchronised lifting, loads of up to 17,000 tonnes can be lifted with utmost precision and safety.
The general contractor on the bridge construction project, Hawaiian Dredging Construction Company, Inc. turned to Enerpac’s strand jacking system when faced with the challenge of placing precast concrete girders more than 60 metres long across a gorge more than 60 metres deep.
The new bridge is part of Hawaii Route 19, which is the main artery between the cities of Hilo and Kona on the largest island of Hawaii.
According to Hawaiian Dredging project superintendent, Glenn Koki, this was the first time in Hawaii that concrete girders were used for such a long span. There were six girders, each about 64m long and weighing 135 tons each.
The girders were pre-cast in Washington State in nominal 15.25m sections and brought by ship to Hawaii. Onsite, the delivered girder sections were positioned on combination fabrication-and-launch tables where they were spliced and tensioned to form the final 64m long girders.
Working support across the gorge was provided by a prefabricated truss bridge from Acrow Corporation of America.
In order to utilise the strand jacks, lifting towers were erected at each end-point of the girder to be placed. The width of the lifting towers was just sufficient for placing one girder, and then the towers were moved to the next placing position.
Prior to actual lifting, the Hawaiian Dredging crew trained with a strand jack on a miniature version of a lifting tower.
Strand lifting is particularly useful where loads need to be raised or lowered over long distances and where operators need maximum stability and precision control over the lifting process.
“Because the multiple jacks can be moved in unison and with great precision, heavy structures can be assembled at ground level (with increased safety and reduced cost) 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,” says Enerpac Integrated Solutions Australasia manager Mr Colin Chapman, who has been involved in some of Australia’s major industrial and infrastructure projects including pipeline, resources loader, ports, petroleum, heavy lifting and materials handling projects.
Designed to complement cranes and other lifting systems, the maximum lifting capacity of the strand system is determined by strand capacity rather than the abundant capacity of the hydraulic cylinders, which are types already employed worldwide with outstanding reliability, says Colin Chapman.
Enerpac’s projects globally range from lifting of entire buildings and bridges (including the Golden Gate Bridge) to splitting of mining draglines for maintenance and construction of offshore oil rigs.
Recent projects that employed strand jacking systems include construction of the world’s highest viaduct, the Millau viaduct in Southern France, which at 300 metres is the highest road bridge in the world, twice as high as the top of the Sydney Harbour Bridge and taller than the Eiffel Tower.