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Two thousand years after the Romans built for some of history\'s most celebrated arches, one of their ancient cities has given rise to a new engineering feat that reflects their triumphs. The Third Millennium Bridge at Zaragoza, Spain\'s fifth big city - formerly the Roman fluvial port of Caesaraugusta, serving the Ebro Valley of Spain - is a showpiece of the city\'s Expo 2008 and one of the world\'s most amazing bridges. With its elegant complex structure surmounted by a concrete bowstring arch, the 36 million Euro structure by architect Juan Jose Arenas involved a unique feat of hydraulic engineering.
As the deadline loomed for the Expo from June14 - September 14 (2008) - and with only three days in which to complete the job - a PLC-controlled Enerpac Synchronous lifting system was employed to delicately and precisely ease apart a 12.000 ton load to make space in the crown of the arch for the bridge\'s final concrete casting.
Delicate hydraulic crown jacking procedure shapes the concrete bowstring arch of Zaragoza\'s Third Millenium Bridge.
Just as the Romans used advances in the technologies of concrete and hydraulics to build their aquaducts and triumphal arches, so construction company Dragados turned to the advanced Enerpac PLC-controlled hydraulic technology to perform the world record in the crown jacking of the arch of The Third Millennium Bridge (which has a total length of 270 m, a 216 m span, a 48 m wide deck and a total 68 m overall width, including 6 traffic lanes and 2 bicycle lanes. The entire structure is made of high-strength concrete).
The crown jacking of the bowstring arch was done using a synchronous system with six 2000 tons double-acting lock nut cylinders controlled by a single PLC-control unit.
"Concrete is an unusual choice for such a large bridge with such a unique configuration, and that presented the challenge of performing a world record crown jacking operation carried out by Dragados using the hydraulic solution supplied by Enerpac," said Jesus Gonzalez, technical director of Enerpac in Spain.
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"The most crucial operation of the construction process, which took place in the first week of April 2008, was the jacking apart of the crown of the bowstring arch. This was done using the Enerpac synchronous hydraulic system with six double-acting lock nut cylinders, each with a lifting capacity of 2000 tons and with all six jacks monitored by a single PLC-control unit. "This integrated hydraulic system was used initially to move the arch and push the cantilevers apart to make space for the final casting. Then it was employed to provide hydraulic jacking to tension the cables and raise the deck to its final position," said Jesus Gonzalez.
The success of the project depended crucially on the smooth and safe implementation of delicate jacking procedure as part of the project\'s critical path. With three days to complete the crown jacking of the arch, engineers needed absolute precision, reliability and safety as they struggled against the Expo 2008 deadline in the summer of northern Spain.
The success of the Zaragoza\'s Third Millenium Bridge project depended crucially on the smooth and safe implementation of delicate hydraulic jacking procedure as part of the project\'s critical path.
Jesus Gonzalez says the custom-designed synchronous system was engineered to push apart and hold the two parts on the top of the arch, leaving the arch totally un-swung. This precision operation involved an electronic programmable system that synchronized three pairs of cylinders with a precision of half a millimetre between leading and trailing points of the jacks, and which tolerates a disalignment of loads of 30 tons among them. The system imposes a load on the arch of slightly more than 12.000 tons to permit the jacking and closing operation 36 meters above the deck of the bridge, he explains.
Two phases of the bridge construction used the Enerpac Synchronous System. First, the deck of the bridge was built with a pushing system that slid the structure on provisional pivots. This involved a system of electronic monitoring of eight lines of cylinders, of 150 tons each.
The custom-designed synchronous system was engineered to push apart and hold the two parts on the top of the arch, leaving the arch totally un-swung. Featuring the highest arch in the world of a fluvial bridge, execution of the project was made possible in large part by the synchronized systems developed by Enerpac\'s Integrated Solutions centre of Spain.
The arch was constructed in the second phase, with the three pairs of cylinders involved governed by a 1600 bar pressure-transducer and a race sensor. A computer-based synchronization was carried out with specific software developed to take account of roll as the arch opened, while controlling individual loads per cylinder as well as pairs of cylinders.
The system was designed with automatic failsafe functions to automatically halt the operation and hold the load if its synchronisation was interrupted.
