A PLC-controlled Enerpac synchronous lifting system was employed to ease apart a 12.000 ton load to make space in the crown of the arch for the bridge's final concrete casting. The Third Millennium Bridge at Zaragoza, Spain was one of the major attractions of Expo 2008 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. Construction company; Dragados turned to the advanced Enerpac PLC-controlled hydraulic technology to perform the crown jacking of the arch of The Third Millennium Bridge.
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. Jesus Gonzalez, technical director of Enerpac in Spain, said that the 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.
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 northern summer.
Gonzalez added that 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 synchronised 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. Gonzalez further explained that 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.
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. Execution of the project was made possible in large part by the synchronised systems developed by Enerpac Integrated Solutions.
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 synchronisation 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.
Available in configurations from 4 to 64 lifting points, synchronous lifting systems electronically control and monitor movement during the hydraulic raising, lowering, positioning or testing of heavy objects such as:
- Manufacturing machinery
- Manufactured structures
- Oil platforms
- Mining equipment
- Heavy but delicate computerized and electrical equipment
The premium version of Enerpac’s computer-controlled Enerpac synchronous hydraulic lifting system can be used with multiple cylinders ranging from 10 to 1000 tonnes capacity each. The system uses digital synchronisation control accurate to within a 0.1 millimetre between leading and lagging lifting points.
Operating through PLC control with touch-screen simplicity, the 700-bar system offers maximum stroke to finely balance complex, delicate and potentially hazardous structures. A major benefit is load balancing and removal of internal stresses. Synchronous lifting overcomes the problems which are generally associated with manual control.