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A great new work of French Structural Engineering and Spanish/American Hydraulic Technology
Hydraulic system lifts intermediate temporary piers |
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When the Millau Viaduct was being designed, Eiffel, a subsidiary of the Eiffage Group and dedicated to steel construction, estcylinders_filested that seven intermediate temporary piers were required between the definitive piers in order to be able to 'launch' the deck during its construction.
Two of the temporary piers, at the ends of the structure, will be directly installed by crane as they only measure 20m and 12m high, but the height of the remaining 5 piers range from 87,5m to 163,7m. For this purpose a telescopic system has been designed for lifting the temporary piers, the hydraulic portion |
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Telescopic System |
of which will be executed by Enerpac's local office in Spain.Once a pier has been raised the machinery including the hydraulic system, is disassembled and moved to the location for installation of the following pier. The telescopic system exists of two parts:
- The first is a cubic structure of 12m bases, containing the entire system, fitted with 'toothed racks' graduated in meters at its vertices.
- The second comprises the hydraulic cylinders and hydraulic control system forming the lifting mechanism. The hydraulic cylinders are installed at the four vertices of the cube, anchored to supports linked to the toothed rack and which, thanks to the successive insertion of locking chocks in the toothed rack, permit the vertical displacement of both the pier structures and the hydraulic machinery, guided by the structure of the machine.
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| 1000 mm lifting steps |
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The operating process is simple; the supports for the cylinders are locked in the toothed rack by means of chocks, whilst the structure of the pier is free. The operators, using controls provided with comprehensive software that incorporates all kinds of safety options, starts pumping oil to the cylinders, thus raising the rams that thrust against the structure of the pier. In this way cylinders raise the structure of the pier to the next perforation in the toothed racks. The cylinders have a stroke of 1100 mm and the 'toothed rack' has notches every 1000 mm, such that there are 100 mm available to compensate for possible unforeseen circumstances. Each hydraulic cylinder has its own control, with the option of immediate locking, and sensors of all kinds in order to take cognizance of any unforeseen circumstance (wind, temperature, etc), which makes an adjustment in the raising of the pier structure necessary, each cylinder rising independently. Once the desired height has been attained, the structure of the pier is locked with |
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| The Enerpac Hydraulic System |
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| chocks and then the cylinder support chocks are freed. The rams are withdrawn and the bodies of the cylinders are raised together with their supports to the toothed rack perforation immediately above, where they are then locked with chocks. In this manner both the structure of the pier and the hydraulic machinery are raised by 1m, the process then being repeated until the first element projects beyond the structure of the machine, being locked underneath. Once it has concluded its function and because it now weighing less, the hydraulic system is lowered to the bottom position by crane; once it is on the ground a second element of the pier is mounted on it and one proceeds in the same way until the entire temporary pier has been completed, at which point the deck can be pushed out over the new pier. |
| Controlling the process |
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| This lifting process must be very strictly controlled and thus the hydraulic cylinders are fitted with an internal position transducer. Similarly the pressure lines have pressure transducers, all being located internally such that they are protected from inclement weather, dirt, humidity, etc. All the information is brought together at a control panel, which, by means of a PLC, manages the data and sends orders to the electro valves, the raising of the cylinders being executed from within an established program.
The control panel allows the operators to be aware at all times of the load and position of each of the cylinders and if necessary, to stop their advance if any of the system variables exceeds the maximum limits laid down. |
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Hydraulic Climbing System |
The system has been designed not to permit a deviation at any time in excess of 3 mm in height, or a maximum 5% load difference between each of the cylinders.
Each cylinder has its own hydraulic pump such that, if necessary, each cylinder can be operated individually, always provided that an exhaustive protocol of request for, and granting, permission is carried out from the central application. The operators, located at each end of the structure, have controls connected to the central control by means of which they validate, at all times during the process, the insertion or withdrawal of the chocks.
Once the signal has been received, the person in charge of the central control will give the order to continue the process. In addition there are oil level and temperature monitors and alarms that stop the advance should there be any unforeseen circumstance, such as pressure drop, cable breakage, etc.
Technical specifications
The hydraulic portion of the machine comprises four cylinders, each of which is fed by its own pump, all centralized at a central control panel. Each assembly has a 511 tonnes thrust capacity, thus overall they have a maximum thrust capacity of 2044 tonnes. A 420 tonnes requirement is not expected to be exceeded during normal operating cycles, in this way the assembly has been designed with a generous safety margin. The nominal pressure is 700 bar and the stroke of the cylinders, as already mentioned, is 1100 mm. An overload of 675 tonnes is acceptable with a ram extended and 1500 tonnes with a withdrawn ram. The entire control system (cabling, control panel, visual display units, etc) is protected against the elements and electromagnetic disturbance and against accidents and possible impact during installation and operation. |
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High
Pressure Hydraulics 
